New low-cost ($170) 100MHz Differential scope probe from Micsig

[mikeselectricstuff]

Micsig just launched a new 100MHz HV differential probe

According to their mailshot

Dear customer, We're honored here to introduce our new product: Micsig High Voltage Differential Probe! We tested it compared with Tektronix P5200A, it works extremely good

They did offer to send me one, but I just don't have time at the moment..

[nctnico]

Micsig just launched a new 100MHz HV differential probe

According to their mailshot

Dear customer, We're honored here to introduce our new product: Micsig High Voltage Differential Probe! We tested it compared with Tektronix P5200A, it works extremely good

They did offer to send me one, but I just don't have time at the moment..

Same here. I'm wondering whether it is a rebrand or their own design. In case of the latter it would be nice to do a teardown. Also I would like to be able to plug in a banana to BNC connector instead of the flying leads to be able to use it up to 100MHz.
Still the USB power and loop through is a nice touch.

[EEVblog]

Too bad it's X50 and X500.
Max voltage is not much higher than the more useful X10/X100 probes.

[TheAmmoniacal]

Looks great, they should send me one. I'll do a review!

[mikeselectricstuff]

Too bad it's X50 and X500.
Max voltage is not much higher than the more useful X10/X100 probes.

Yes, just noticed that. Could be be limiting for measuring lower level signals, especially on scopes that force BW limit on at low mv/div settings.

[kirill_ka]

And they offer it for $100 if bought with oscilloscope... I couldn't resist.

[cdev]

Seems like a very good thing to have around.

Literally could be a life saver for some people!

[alm]

Note that $170 is the introductory offer. According to the AliExpress listing the normal price is $283, which is less of a deal.

Also I would like to be able to plug in a banana to BNC connector instead of the flying leads to be able to use it up to 100MHz.

The flying leads are fairly short and can be twisted, so I imagine they work well enough up to 100 MHz. I guess they could have used an insulated BNC connector, but accessories for those are kind of rare and might be inconvenient for field work. They may also not be much better for common mode rejection because of their unbalanced nature. And would invite even longer leads. At that point you might as well be using a stand-alone differential amplifier.

[lukier]

And they offer it for $100 if bought with oscilloscope... I couldn't resist.

Damn, I bought Micsig scope over a week ago. Should've waited a bit.

[casinada]

Hantek Version around the same price also x50 x500: $188
http://www.ebay.com/itm/Hantek-High-Voltage-Isolate-Pro-Probe-Measurement-100MHz-3-5ns-Over-Range-Warn/282370784441?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

[djacobow]

I like that for the 5V you can plug it into the scope's USB port (I presume). Much better than battery alway dying.

[alm]

And more versatile than proprietary probe power connectors as often used by brand-name probes.

We will have to wait for reviews to see about performance and safety. I am especially curious how the common mode rejection ratio (CMRR) will fare at high common mode voltages (voltage coefficient in the attenuators). But maintaining its CMRR across the common mode voltage range might be expecting too much from a cheap differential probe.

[cdev]

I'm sure they would give you the discount. Just ask them.


Quote from: lukier on Today at 15:02:23>Quote from: kirill_ka on Today at 13:44:06

And they offer it for $100 if bought with oscilloscope... I couldn't resist.

Damn, I bought Micsig scope over a week ago. Should've waited a bit.

[DK-1]

I seen the same probe yesterday on Aliexpress and i was curious.....
So i wait for some more info/opinion and almost sure i ll buy one because i've need one more....especially in this price range is really interesting.

[TK]

And they offer it for $100 if bought with oscilloscope... I couldn't resist.

Damn, I bought Micsig scope over a week ago. Should've waited a bit.

I am sure you can still get it for $100 if you ask micsig.

[EEVblog]

And they offer it for $100 if bought with oscilloscope... I couldn't resist.

Damn, I bought Micsig scope over a week ago. Should've waited a bit.

I am sure you can still get it for $100 if you ask micsig.

At a $100 ask if you can buy two.

[Dubbie]

Yeah, the first thing I thought when I got Daves probe a week or two ago... "I wish I had two of these"

[TheSteve]

If they did start selling them at 100 bucks they would be backordered pretty darn fast.

[nidlaX]

This is supposed to be their own design, not a rebadge.

Would anyone with high voltage / transient testing equipment like to do a teardown / review of this probe? joeqsmith perhaps? 

[BravoV]

Kudos for the 5V power input, as it can be powered by ordinary cellphone's power bank.

[tautech]

Kudos for the 5V power input, as it can be powered by ordinary cellphone's power bank.

More so for the USB jack on the side so they can be daisy chained. 
Someone was using their gray matter. 

[Hydron]

Very tempting... just wish it had been out long enough for some reviews. Thanks for the heads up!

Has anyone (maybe Mike?) had experience getting Micsig stuff into the UK? If it's likely to get caught up in customs with extra fees and delays then it might be easier paying a bit more and buying within the EU.

[mikeselectricstuff]

Very tempting... just wish it had been out long enough for some reviews. Thanks for the heads up!

Has anyone (maybe Mike?) had experience getting Micsig stuff into the UK? If it's likely to get caught up in customs with extra fees and delays then it might be easier paying a bit more and buying within the EU.

I've never had customs issues cause significant delays - depending on the courier, they either contact you for payment before it arrives in UK, or send an invoice later.  For higher value items, the brokerage fee is relatively small compared to what an EU distributor will charge as their markup. The rest is VAT which you'd pay either way. I don't recall if the full value had been declared.

[lukier]

I've messaged Micsig on Aliexpress, well see if I can get the promo deal.
If I get the probe I can write a mini-review here and maybe compare it with Tek P5205 which I got from eBay "for parts or repair" (cable cut) a while ago.

[Mechatrommer]

Kudos for the 5V power input, as it can be powered by ordinary cellphone's power bank.

More so for the USB jack on the side so they can be daisy chained. 
Someone was using their gray matter. 

not enough grey matter. that thing need mains supply or power bank around in order to work. i wish someone has enough wisdom of using 2 rechargable li-on stacked inside (preferably 18650 size hence easily replacable) 7.2V with charging circuitry (from 5V USB) that doesnt block operation during charging (ie charging while probing)...

[tautech]

Kudos for the 5V power input, as it can be powered by ordinary cellphone's power bank.

More so for the USB jack on the side so they can be daisy chained. 
Someone was using their gray matter. 

not enough grey matter. that thing need mains supply or power bank around in order to work. i wish someone has enough wisdom of using 2 rechargable li-on stacked inside (preferably 18650 size hence easily replacable) 7.2V with charging circuitry (from 5V USB) that doesnt block operation during charging (ie charging while probing)...

Well until somebody does a teardown we'll never know.
DC-DC convertor ..................

[simone.pignatti]

In case of interest, we have the combo kit (2x) at Euro 185 + VAT

[TheAmmoniacal]

What do you mean by a combo-kit? Two units?

[simone.pignatti]

Yes

[TheAmmoniacal]

If I wasn't on vacation at the moment I'd likely go for it.. Do you want VAT too?

[simone.pignatti]

Better to stay in holiday
About VAT, yes it is mandatory within EU but not for registered company.

[Hydron]

In case of interest, we have the combo kit (2x) at Euro 185 + VAT

I am very interested, can you PM me the details of how to place an order for the combo kit?

Only thing that stopped me already ordering one is that nobody seems to have testedd one to check if it does what Micsig says (i.e. noise level, bandwidth etc). Have you tried one of these probes out yourself?

[TheAmmoniacal]

That's why we need a review and a teardown, but mike is busy.

What about a side-by-side comparison with Dave's diff probe? Drawbacks of 50X/500X vs. 10X/100X.

[simone.pignatti]

In case of interest, we have the combo kit (2x) at Euro 185 + VAT

I am very interested, can you PM me the details of how to place an order for the combo kit?

Only thing that stopped me already ordering one is that nobody seems to have testedd one to check if it does what Micsig says (i.e. noise level, bandwidth etc). Have you tried one of these probes out yourself?

message sent

[Mechatrommer]

Kudos for the 5V power input, as it can be powered by ordinary cellphone's power bank.

More so for the USB jack on the side so they can be daisy chained. 
Someone was using their gray matter. 

not enough grey matter. that thing need mains supply or power bank around in order to work. i wish someone has enough wisdom of using 2 rechargable li-on stacked inside (preferably 18650 size hence easily replacable) 7.2V with charging circuitry (from 5V USB) that doesnt block operation during charging (ie charging while probing)...

Well until somebody does a teardown we'll never know.
DC-DC convertor ..................

from the spec, the power supply is DC 5V and USB, no mentioning of battery size or unplugged operating hour, no power switch etc. i have suspicion there is no battery in there.

[simone.pignatti]

Correct, no battery. the pic shows what we have

[Jeroen13]

In case of interest, we have the combo kit (2x) at Euro 185 + VAT

Do you have a webshop or just 2 probe spare ?

[simone.pignatti]

we have a webshop 

[Jeroen13]

Just ordered 2 pieces, will try to compare it to Tek THDP0200 and Tek IsoVu TIVM at work when I have them.

[simone.pignatti]

thanks, shipping out today

[JPortici]

Hi simone, for how long are you going to do this promotion?

[simone.pignatti]

ciao, for sure till September '17

[2N3055]

With a 500X probe, noise is potentially problematic...
Does anybody know what is noise spec ..?

[simone.pignatti]

?40mVrms (50X)

?230 mVrms (500X)

[Hydron]

Input referred noise spec:
?40mVrms (50X)
?230 mVrms (500X)

An example of pk-pk noise (measured by Micsig, compared with Tek P5200A) can be seen on the aliexpress listing linked in the OP.

If the noise spec (and other specifications) are true, these could be a really good deal if the somewhat low sensitivity (50x) is OK for the intended application.

edit: see http://www.micsig.com/UploadFiles/file/High%20Voltage%20differential%20probe.pdf
I note the oddity of 75R output impedance though - not an issue if it's driving 1Mohm input, but unusual and annoying if you want to drive 50R! Is this really the impedance, or is it a typo?

[nidlaX]

Input referred noise spec:
?40mVrms (50X)
?230 mVrms (500X)

An example of pk-pk noise (measured by Micsig, compared with Tek P5200A) can be seen on the aliexpress listing linked in the OP.

If the noise spec (and other specifications) are true, these could be a really good deal if the somewhat low sensitivity (50x) is OK for the intended application.

edit: see http://www.micsig.com/UploadFiles/file/High%20Voltage%20differential%20probe.pdf
I note the oddity of 75R output impedance though - not an issue if it's driving 1Mohm input, but unusual and annoying if you want to drive 50R! Is this really the impedance, or is it a typo?

It is actually 75 Ohms according to their engineering department. I told them it's a strange choice, not sure why they made this decision. Keep this in mind if you decide to use a BNC cable extension.

By the way, if anyone finds any typos in or needs clarifications regarding anything in the user manual, let me know.

[DK-1]

I bought 2 just now!
For this price i was too much curious to try it, when arrived i will tell something

[nctnico]

Is there any CAT rating on this differential probe? Without it I wouldn't want to use it on anything mains powered.

[alm]

It does not appear to be silkscreened on the case or printed in the datasheet, so I would assume not. Probably no independent testing either. So safety for mains voltages is suspect.

[Mechatrommer]

Input referred noise spec:
?40mVrms (50X)
?230 mVrms (500X)

An example of pk-pk noise (measured by Micsig, compared with Tek P5200A) can be seen on the aliexpress listing linked in the OP.

If the noise spec (and other specifications) are true, these could be a really good deal if the somewhat low sensitivity (50x) is OK for the intended application.

edit: see http://www.micsig.com/UploadFiles/file/High%20Voltage%20differential%20probe.pdf
I note the oddity of 75R output impedance though - not an issue if it's driving 1Mohm input, but unusual and annoying if you want to drive 50R! Is this really the impedance, or is it a typo?

It is actually 75 Ohms according to their engineering department. I told them it's a strange choice, not sure why they made this decision. Keep this in mind if you decide to use a BNC cable extension.

By the way, if anyone finds any typos in or needs clarifications regarding anything in the user manual, let me know.

the output coax cable probably 75ohm.just add 75ohm terminator at scope end to get nonoddities 100/1000x figure.

[alm]

If you zoom in onto the AliExpress picture, you can see the silkscreen stating 'Output <= 3 V into 1 MOhm'. So the impedance mismatch would be no worse than with a 50 Ohm output. The only issue that could arise is with extending the cable, but first, you should probably not do that anyway, and secondly I doubt the small impedance mismatch would be that noticeable at only 100 MHz with an unterminated line.

It is an odd choice. I did not even know that you could get 75 Ohm insulated BNC connectors. Maybe they used a video buffer designed for driving 75 Ohm loads?

[nidlaX]

Is there any CAT rating on this differential probe? Without it I wouldn't want to use it on anything mains powered.

I'll get back to you on this, but it is CAT rated according to their R&D. I've asked them to update their catalogue and manuals with this info.

[nctnico]

not enough grey matter. that thing need mains supply or power bank around in order to work. i wish someone has enough wisdom of using 2 rechargable li-on stacked inside (preferably 18650 size hence easily replacable) 7.2V with charging circuitry (from 5V USB) that doesnt block operation during charging (ie charging while probing)...

No, they got it right! You power it from the scope's USB port and MicSig's tablets already have a battery inside. So why use an extra battery inside the differential probe?

[exe]

No, they got it right! You power it from the scope's USB port and MicSig's tablets already have a battery inside. So why use an extra battery inside the differential probe?

To use it with other scopes?

[nctnico]

No, they got it right! You power it from the scope's USB port and MicSig's tablets already have a battery inside. So why use an extra battery inside the differential probe?

To use it with other scopes?

Those have USB ports too so no problem.

[Jeroen13]

Comparison between Micsig DP10013, Tektronix THDP0100, TekTronix TIVM05 on a Tektronix 5 series MSO58



High-side gate-emitter (IGBT) with 400V switchnode:




400V switch node:




Overall I think it is a very good probe especially for that price. The measurement leads are a bit long which probably causes some extra ringing.

[BravoV]

Jeroen13, thank you for the comparison ! 

[EEVblog]

Is there any CAT rating on this differential probe? Without it I wouldn't want to use it on anything mains powered.

FYI my HVP70 probe is fully independently tested and CAT III rated.
I also have the full test report for it with test photos and setup etc, some of which I think I showed in the CE mark video.

[BravoV]

Is there any tear down photos of it's internal yet ? ... wishful thinking ... 

[wraper]

Actually it's $160, not $170 if you click to claim $10 off coupon

Spend US $120.00 to get US $10.00 off.
(includes shipping costs)
Expires 2017/07/25

[Hydron]

Actually it's $160, not $170 if you click to claim $10 off coupon

Spend US $120.00 to get US $10.00 off.
(includes shipping costs)
Expires 2017/07/25

...or just over $100 each (plus 22% tax, ouch) if you order 2 for 185 EUR like I just did

If a teardown hasn't already gone up by the time I receive mine then I'll have a look inside and post some pics. Jeroen13 - thanks for the measurements, they gave me enough confidence to buy a couple.

[Electro Detective]

I prefer to wait for Christmas and get the EEV probe for a tad more than the generic Pintek and know what I'm getting   

otherwise I'll stick to proven old school techniques in the meantime   


Unless the teardown of this cheapie isn't too shabby for 50 hz prod work   

[JPortici]

Comparison between Micsig DP10013, Tektronix THDP0100, TekTronix TIVM05 on a Tektronix 5 series MSO58

[porn]

Overall I think it is a very good probe especially for that price. The measurement leads are a bit long which probably causes some extra ringing.

thanks for the photos. very jealous of the test setup

[jacklee]

  

[Hydron]

From the pics it looks like the front end is handled by one of these:
http://www.analog.com/media/en/technical-documentation/data-sheets/ADA4817-1_4817-2.pdf

Won't be able to confirm until better pics come along or mine arrives though.

[H.O]

The USB jack on the side is labeled power output but do they feed both power and data thru to that jack so that you can plug your thumb drive into it when the scopes USB jack is occupied by the probes "power cable"?

[alm]

What surprises me is that they went through the trouble of using an insulated BNC connector, presumably because the Micsig scopes can be operated without a ground connection, and so the shell is not guaranteed to be at a safe potential. But then use USB connectors that most likely have their shell connected to the BNC shell. They could have used a deep barrel connection, like on some Fluke/Agilent differential probes, if they were worried about safety.

Does the manual say anything about requiring a grounded scope?

[PartialDischarge]

Just ordered a couple.
I'm actually thinking of 'upgrading' one of them to x50, x1000... lets see how I'll do that.

[nctnico]

@Jacklee: do you have a picture of the solder side of the board? I'm wondering whether the USB interface is fully routed so you can plug a USB stick into the probe.

[Hydron]

Just ordered a couple.
I'm actually thinking of 'upgrading' one of them to x50, x1000... lets see how I'll do that.

From looking at the PCB picture there are a few things which might make changing the gain of these difficult:
- The input divider is only 5x SMD resistors/capacitors. This will be difficult to run at higher voltages than 1.3kV (look at voltage ratings of SMD resistors - even special HV ones do not have high voltage ratings)
- The gain change appears to be done after the input stage. If the input of the ADA4817 is at the limit of it's common mode input rating at 1300Vin then the input divider ratio would have to be changed, rather than just the gain resistors for the range you want to modify.
- Other than the trimcaps/pot on the the input (for CMRR) all other trimming (for offset etc) seems to be done digitally, probably during production. If this varies with different ranges then it could be tricky to get right if you change the gain of one range.

That said, hopefully it doesn't end up too hard to mod these - personally I'd be interested in changing at least one to 20/500X for (hopefully giving lower noise on small signals)

I'm a bit confused myself as to how the gain switching is being done - there appear to be 2 different sets of series resistors between the input and output amplifier stages (switched via the relay) but this would be a nightmare to match for correct CMRR, so I'm not sure how it's being managed or if I'm completely wrong in my analysis. Has anyone got any ideas? I second the request for solder-side.

[tautech]

Request:
Please identify U7.

[nctnico]

Request:
Please identify U7.

Looks like an isolated DC-DC converter.

[Floyo]

For the price/introduction deal they seem pretty good. I like the USB power option, the supplies are just so ubiquitous, there are probably at least five sockets around the bench at any time. I have the Pintek DP25 with its center negative 9V barrel jack, and that is slightly less than ideal for a few reasons.

It looks to me like they used an isolated DC-DC brick for powering the probe, there seems to be a lack of traces between both sides of U7,
possibly indicating isolation. But then the data traces of the "host" USB-A port seem to sneak off to R99/R100 right close to the "secondary" circuitry, so that contradicts the isolated theory.

[tautech]

Request:
Please identify U7.

Looks like an isolated DC-DC converter.

Yes of course.

Its specs will be interesting. 

[PartialDischarge]

Just ordered a couple.
I'm actually thinking of 'upgrading' one of them to x50, x1000... lets see how I'll do that.

From looking at the PCB picture there are a few things which might make changing the gain of these difficult:
- The input divider is only 5x SMD resistors/capacitors. This will be difficult to run at higher voltages than 1.3kV (look at voltage ratings of SMD resistors - even special HV ones do not have high voltage ratings)
- The gain change appears to be done after the input stage. If the input of the ADA4817 is at the limit of it's common mode input rating at 1300Vin then the input divider ratio would have to be changed, rather than just the gain resistors for the range you want to modify.
- Other than the trimcaps/pot on the the input (for CMRR) all other trimming (for offset etc) seems to be done digitally, probably during production. If this varies with different ranges then it could be tricky to get right if you change the gain of one range.

That said, hopefully it doesn't end up too hard to mod these - personally I'd be interested in changing at least one to 20/500X for (hopefully giving lower noise on small signals)

I'm a bit confused myself as to how the gain switching is being done - there appear to be 2 different sets of series resistors between the input and output amplifier stages (switched via the relay) but this would be a nightmare to match for correct CMRR, so I'm not sure how it's being managed or if I'm completely wrong in my analysis. Has anyone got any ideas? I second the request for solder-side.

The input resistors shouldn't be a problem, both the voltage rating and power have to be considered. There are hv smd resistors, easy to buy 3kv ones at 2512 size, 1kV @1210 . At 2500V input however 5 1Meg resistors in series will dissipate 250mW each and those in the picture don't seem big enough. The input compensating ceramic caps would need to be upped in voltage rating too

The gain setting is another story of course that will have to be studied. I hope that it is not fixed before the diff amplifier as you mentioned, that would be weird.

The frequency compensation that goes along these dividers will get affected too and a before/after comparison in a network analyzer will come in handy.

This is something Ill look into as I'm very interested in having the input limit raised to about 2500V

[Hydron]

The input resistors shouldn't be a problem, both the voltage rating and power have to be considered. There are hv smd resistors, easy to buy 3kv ones at 2512 size, 1kV @1210 . At 2500V input however 5 1Meg resistors in series will dissipate 250mW each and those in the picture don't seem big enough. The input compensating ceramic caps would need to be upped in voltage rating too

I was deliberately being a bit pessimistic about the voltage ratings - was assuming that the working (not overload) voltage was used, and that you'd want a reasonable safety margin on top. At 1206 (my guess from the pictures) you can get 400V/1kV working/overload voltage at a reasonable cost, higher if you pay more, but I'd start to worry about creepage/clearance distance too much above this, and also power dissipation as you mentioned. If I were to push towards 2.5kV I'd count on changing a few things, though at the price it's OK to take a risk modding one!.

As for the gain question, I think the mystery will have to wait for better PCB pictures or for the courier to show up with mine (hopefully thursday).
All I can see is what looks to be 2 single ended input amplifiers (in the ADA4817), followed by traces going via the relay (appears to be 2 per side) to a differential-to-single ended amplifier in the SOT23-5 package driving the output. Unless I'm interpreting the signal flow incorrectly and it's actually connected like an instrumentation amplifier (with gain adjusted via a single resistor) then I don't understand how the gain could be switched by the relay.

Other than the questions of how high the input voltage can be pushed and how gain switching is done, I'm please to see that it looks like a promising design with some good parts, rather than just another dodgy clone made by Pintech etc. Hopefully this impression is proved right!

[PartialDischarge]

Other than the questions of how high the input voltage can be pushed and how gain switching is done, I'm please to see that it looks like a promising design with some good parts, rather than just another dodgy clone made by Pintech etc. Hopefully this impression is proved right!

Totally, it was time someone made this kind of probe at a reasonable price, given the electronics that these probes pack I never understood the high prices.

Now Micsig please, make a current probe similar to the Tek A6302 

[alm]

Read some posts on the TekScopes list about the complexities of building a low noise DC-MHz current probe before expecting similar performance at an affordable price. As far as I know Tek is still selling pretty much the same probe with different (in some ways worse) electronics and connectors as the old P6042. And they have not been surpassed by competitors in size or noise level.

[PartialDischarge]

Read some posts on the TekScopes list about the complexities of building a low noise DC-MHz current probe before expecting similar performance at an affordable price.

Did you notice the laughing emoji next to my comment? I guess not..

Besides that, what is wrong with "expecting" a new design that lowers the cost dramatically compared to old products while maintaining fairly decent specs?
SDS1202X-E, SSA3021, TO1104.... ring any bells?

[alm]

Has there been a similar advance in ferrite technology and Hall sensors as in ADCs and memory? What would the modern way be of embedding a Hall sensor in a ferrite core with minimal gaps but maximum flux through the sensor?

[PartialDischarge]

I don't know, not my field of expertise. But that does not preclude a drop in price, all manufacturing areas have seen cost/quality/technological improvements. Take an X-ray tube, same vacuum and materials technology now and 40 years ago, but price has dropped a lot.
 

[supercilious]

...or just over $100 each (plus 22% tax, ouch) if you order 2 for 185 EUR like I just did

Where did you get them at this price? Please PM me if you are not confortable posting it in the thread.

[Hydron]

In case of interest, we have the combo kit (2x) at Euro 185 + VAT

Link to this deal: http://www.batterfly.com/shop/micsig-combo-dp10013

As I haven't received my order yet (courier says tomorrow) I can't report on anything except Simone's communication and how long it took to ship, but those were both top notch (friendly and helpful via PM, shipped same day as I paid).

[Hydron]

Just got mine today, have not had a chance to properly check them out but happy with what I have been able to quickly check. For now I've scanned the manual, has some extra info which could be of interest: http://imgur.com/a/Ctycc

Main new things I saw in the manual:
- Overload indication
- Offset self-cal procedure
- 1000V CAT II rating

[CustomEngineerer]

Couldn't find the user manual on Micsig's site, but did manage to find it on Micsig's Amazon site in case anyone is interested and looking.

[mikeselectricstuff]

Has there been a similar advance in ferrite technology and Hall sensors as in ADCs and memory? What would the modern way be of embedding a Hall sensor in a ferrite core with minimal gaps but maximum flux through the sensor?

https://www.aimtti.com/product-category/current-probes/aim-i-prober-520

This uses a fluxgate sensor.

I wonder if there would be scope to adapt a GMR hard-disk head.

[alm]

https://www.aimtti.com/product-category/current-probes/aim-i-prober-520

This uses a fluxgate sensor.

The major advantage is that you can use it without enclosing the conductor. Price is not very low, bandwidth is too low for many applications (5 MHz vs 50 MHz for the Tek), and noise is much worse (8 mA from DC to 5 MHz vs approximately 0.15 mA RMS from DC to 100 MHz). The latter is a big deal in modern circuits that can fly to the moon on 1 mA .

I wonder if there would be scope to adapt a GMR hard-disk head.

This has been proposed before, but I am not aware of anyone actually pulling it off. I would be worried about linearity (both over the bandwidth and over the dynamic range) and dynamic range. A Hall sensor is not necessarily great for linearity and dynamic range either, but Tek got around that by feeding a DC current through the core and using the sensor only as a null detector. Trying to do the same with a disk head might turn out to be more difficult than a Hall sensor and would definitely require some custom magnetics.

[PartialDischarge]

Just received them. This may be the fastest take it apart that I've done on a new item



High voltage silicone cable




Notice the slot to provide isolation between inputs along input divider

[PartialDischarge]

And the board, had to reduce the quality of the pic to meet the 1M limit

Looks like a good design, thanks micsig!

[EEVblog]

What's the J3 pin header on the bottom used for?

[nctnico]

How about the other side of the PCB? I want to see the USB section!

[Hydron]

I assume that J3 is for programming U9, which I think is a Silabs 8051 micro (does DC offset adjustment and controls the gain switching relay). The micro also does DC offset cal when you start it up while pressing both buttons (see manual).

The other side of the PCB is very boring - mostly ground plane, a bit of decoupling and a small circuit that doesn't seem to be part of the signal path. I've attached a (cellphone) pic.

Note that the power input seems to be isolated - there is no DC path from any pin of the USB input connector to the rest of the PCB. The output USB connector has one of it's data pins grounded, the other reads high-z (about 2 Meg) - no idea why they have done this!

IC part numbers I've found so far:
http://www.analog.com/media/en/technical-documentation/data-sheets/ADA4817-1_4817-2.pdf (main input buffer)
http://www.ti.com/lit/ds/symlink/opa2171.pdf (low freq op-amp, involved in offset circuit, marking OPMI)
http://www.analog.com/media/en/technical-documentation/data-sheets/AD8001.pdf (output diff-SE converter opamp)
DC-DC part number is AH4V55V5S-1W, made by "SUCCEED"

I haven't gotten any further working out how CMRR is maintained when switching gains - still looks to be done by switching the ouput resistors between the ADA4817 and the AD8001 from 100 to 1000 ohms. This continues to not make sense to me as i would have thought that CMRR matching would be a nightmare due to needing to match 2 resistors + relay contact resistance between 2 separate ranges. I'll look into it further to try and make some sense out of it.

As for CMRR measurements, I measured one probe at 1MHz as ~54/52 dB (50/500x) and the other as ~47/50 dB (i.e. not quite meeting spec). At 10MHz I got ~35dB for both ranges on the better of the two probes, but I'm less certain of those numbers.

Edit: forgot to mention that the screws are under the label (ugh) but it thankfully came off without visible damage. There are 6 (!!) of them going into brass threaded inserts, and the case is nice and solid with a decent chance of passing a Dave-test. Plastic fingers from both case halves go into the slot between the HV inputs - I'd say that the resistor/capacitor network would arc over before anything else in this thing. Ouput bnc/cable is not a strong point of this thing (feels cheap, especially compared to the nice case) but i guess it does the job and is easily replaced (at which point the 75R output could be made into 50R).

[IAmBack]

I got mine yesterday. Batterfly claimed that it has newer firmware, hence little delay in shipping. In manual there is "CATII" statement.

[PartialDischarge]

These resistors control the gain, they are 100 and 1K resistor pairs switched by the relay and connected to the output of each op-amp.
Still haven't figured the whole feedback loop though, but it seems that the gain could be controlled at the input stage

[exe]

I got mine yesterday. Batterfly claimed that it has newer firmware, hence little delay in shipping. In manual there is "CATII" statement.

Wait-wait-wait, firmware? In the probe?? Why?

[wraper]

I got mine yesterday. Batterfly claimed that it has newer firmware, hence little delay in shipping. In manual there is "CATII" statement.

Wait-wait-wait, firmware? In the probe?? Why?

Why not? Some chips might be digitally calibrated. Why would they put a number of pots and trimmer capacitors instead? Also didn't you notice there is no hard switch for X50/X500 selection so likely there is MCU for that.

[Hydron]

These resistors control the gain, they are 100 and 1K resistor pairs switched by the relay and connected to the output of each op-amp.
Still haven't figured the whole feedback loop though, but it seems that the gain could be controlled at the input stage

These resistors do look like they control the gain, and are what confuse me. If the ratio between the 100 and 1k resistors on one op-amp varies compared to the other, then you could adjust the input stage to get good CMRR for one range, but on the other it would be terrible. Even 0.1% gain difference limits CMRR to 60dB, and these probes should do better than that at low freq.

There is definitely a MCU involved - it switches ranges (remembering which between power cycles), corrects for DC offset, and is able to perform a self-cal if the offset needs fixing.

[Electro Detective]

The coax shield copper looks green-ish, especially on the bottom solder pad

I've seen that before, usually not good as time passes   

[joeqsmith]

I was asked about running one of these across the small transient generator that I use to benchmark multimeters.   With the probes input, I am sure we could find out at what level it breaks down.   If people wanted to see both l1-l2, l1-gnd and l2-gnd, I could just cycle through them while increasing the level until the probe is damaged.   Like the meters, I could run some sort of highish voltage AC/DC test to make sure it at least handles that.  I didn't see any derate curves for it. 

If any of you have an interest in seeing one tested to failure, or have some specific potentially destructive test you would like to see ran, feel free to post.   

Looking at the pictures, my concern would be at the faster edge rates putting a lot of stress on the two resistors in series with the cap string.   Without someone sketching out the front end, hard to say but seem like these two resistors, assuming they clamp on the back side of the caps, would go first to go.  No schematic or probe, so a total guess on my part.   No derate, seems I would be allowed to hammer it and it should survive. 

[tautech]

DC-DC part number is AH4V55V5S-1W, made by "SUCCEED"

Google can't find it.
Wonder how much isolation it provides ? Could it be the limiting component for this units voltage ratings ? 

[nctnico]

DC-DC part number is AH4V55V5S-1W, made by "SUCCEED"

Google can't find it.
Wonder how much isolation it provides ? Could it be the limiting component for this units voltage ratings ? 

Perhaps someone can post a picture to see if it has the right UL markings.

[wraper]

DC-DC part number is AH4V55V5S-1W, made by "SUCCEED"

Google can't find it.
Wonder how much isolation it provides ? Could it be the limiting component for this units voltage ratings ? 

Why would it matter a tiny bit. The only thing it isolates is 5V power from USB. Output to the scope is directly connected to the rest of the circuit.

[nctnico]

DC-DC part number is AH4V55V5S-1W, made by "SUCCEED"

Google can't find it.
Wonder how much isolation it provides ? Could it be the limiting component for this units voltage ratings ? 

Why would it matter a tiny bit. The only thing it isolates is 5V power from USB. Output to the scope is directly connected to the rest of the circuit.

After some thought I have to agree. IMHO the DC-DC converter is there to prevent ground loops and not to provide a safety isolation barrier.

[exe]

Why would it matter a tiny bit. The only thing it isolates is 5V power from USB. Output to the scope is directly connected to the rest of the circuit.

Wait-wait-wait, so this thing is not safe? Like, if I touch touch-screen on my scope I can get electrocuted? Or if I touch ground lead of another probe?

Also, the scope itself is only cat 1...

[alm]

The input impedance of the probes should be sufficiently high (>= 4 MOhm to common?) to limit the current through them to a safe level. But it is often recommended to make sure the scope is grounded when using a differential probe. Since the differential probe is not isolated, hooking both probes to a high potential could still pull the scope to the same high potential. Depending on the capacitance, that could be painful.

The opposite problem is if the scope floats too far from the device under test. Then you may exceed the maximum common mode voltage of the probes, distorting the signal. By tying the scope to ground, you make it more likely that it will be close(ish) to the device under test (if that is also ground referenced somehow).

I do not know what the Micsig manual says about ground connections. If you make sure the scope is grounded, then you should be able to safely touch the scope without fear of shocks.

[nidlaX]

The input impedance of the probes should be sufficiently high (>= 4 MOhm to common?) to limit the current through them to a safe level. But it is often recommended to make sure the scope is grounded when using a differential probe. Since the differential probe is not isolated, hooking both probes to a high potential could still pull the scope to the same high potential. Depending on the capacitance, that could be painful.

The opposite problem is if the scope floats too far from the device under test. Then you may exceed the maximum common mode voltage of the probes, distorting the signal. By tying the scope to ground, you make it more likely that it will be close(ish) to the device under test (if that is also ground referenced somehow).

I do not know what the Micsig manual says about ground connections. If you make sure the scope is grounded, then you should be able to safely touch the scope without fear of shocks.

Last I recall, the manual does ask the user to ensure the scope is properly grounded. Then again, all of their scopes can be battery powered, so I'm not sure how many people will be following those guidelines.

[exe]

Last I recall, the manual does ask the user to ensure the scope is properly grounded.

My scope has 1k resistance to ground when powered from mains. Is this a proper ground?

[nidlaX]

Last I recall, the manual does ask the user to ensure the scope is properly grounded.

My scope has 1k resistance to ground when powered from mains. Is this a proper ground?

Well, the Micsig scopes use a DC input, no direct chassis ground. Someone else can comment on safety in this situation. If you were using a traditional scope, it should have a direct connection between the chassis shell to earth.

[alm]

I think it should be sufficient in combination with the differential probe, since 1 kOhm is still low compared to the MOhm impedances from the probe.

I am not so convinced it is also safe with passive single-ended probes. If you clip the ground lead to say 230 V, it may trip the GFCI, but not every circuit is protected by a GFCI. The current of 230 mA will not be enough to blow a fuse. So the ground connection is not ensuring the scope is at a safe potential. This assumes that the connection to ground is purely resistive, Things might be better if there is an element that decreases in resistance at higher voltages (e.g. TVS, NTC). Maybe someone more familiar with these scopes can comment.

[David Hess]

If a differential probe is used with an isolated input or an oscilloscope with a missing ground connection, then the input or the oscilloscope if its ground connection is missing will charge to the common mode input voltage which can be considerable resulting in potential damage to the oscilloscope.  Tektronix includes a specific warning with their high voltage differential probe not to use it with an isolated oscilloscope input like on their TPS series.  Note that the attenuation of the probe make no difference since the attenuators go to the now isolated ground.

I suspect the isolated DC to DC converter is not there for safety but to prevent a ground loop between the oscilloscope's own USB connection and its vertical input and between any other USB power supply if used and the oscilloscope since they will likely share ground through the AC power connection.

[2N3055]

Hi, Just spoke with Telonic in the UK after purchasing a TO1104Z they are still waiting for there first delivery of the probes, the impression i got is that it is a Micsig probe.

https://www.telonic.co.uk/Micsig-DP10013-High-Voltage-Differential-Probe-p/dp10013.htm

At our Italian friends you have a special... You will get 2 for cca. 165 GBP ... Just saying... And they had it on stock, shipped same day.. 
Price for one is pretty much the same..
Just saying..

[boborich]

Anyone tested the bandwidth of the probe? I brought one and tested the bandwidth and I had a difficult time to get 100Mhz out it. My test rig is siglent SDG2122X(hacked from 2042) with sine wave set to 5V P-P without any DC offset, A MDO 3054 500Mhz scope(optioned from 3024). Hock the probe to the scope and set the scope input impedence to 1M without any bandwidth limit. Here is what I got:

At 50Mhz, I got 5.2V P-P.
At 70Mhz, I got 6.8V P-P.
At 80Mhz, I got 7.6V P-P.
At 90Mhz, I got 4.7V P-P.
At 100Mhz, I got 2.7V P-P.

There is a big peaking at 80Mhz starting from 60Mhz, and fall off at 9xMhz at -3db. I don't think this qualifies for a 100MHz probe.

Any thoughts? Am I test it the wrong way?

[TheSteve]

What does it look like if you probe a 50 ohm load on the output of the AWG?

[capt bullshot]

Anyone tested the bandwidth of the probe?
There is a big peaking at 80Mhz starting from 60Mhz, and fall off at 9xMhz at -3db. I don't think this qualifies for a 100MHz probe.

I've seen the same effect with some other 100MHz differential probe.
The root cause for this behaviour are the probes test leads, they are simply too long for a 100MHz bandwith. Try moving them around or twisting them, this heavily influences the frequency response above 60MHz.
IMO a diff probe claiming 100MHz BW but using such long test leads is just nonsense. The probe circuit itself would do a nice 100MHz -3dB rolloff, but using the non-removable leads spoils it all. Same thing as with the ground clip of an ordinary x10 probe, they tend to resonate around 100MHz.

[capt bullshot]

Well, the Micsig scopes use a DC input, no direct chassis ground. Someone else can comment on safety in this situation. If you were using a traditional scope, it should have a direct connection between the chassis shell to earth.

This is not a big deal, a "safety impedance" from the high voltage potential to touchable circuit ground is sufficient. Along with all the minimum distance and creepage requirements. The "safety impedance" is allowed to cross the isolation barrier and is part of it. AFAIR you can find this somewhere in IEC 61010 standards.

[wraper]

Anyone tested the bandwidth of the probe? I brought one and tested the bandwidth and I had a difficult time to get 100Mhz out it. My test rig is siglent SDG2122X(hacked from 2042) with sine wave set to 5V P-P without any DC offset, A MDO 3054 500Mhz scope(optioned from 3024). Hock the probe to the scope and set the scope input impedence to 1M without any bandwidth limit. Here is what I got:

At 50Mhz, I got 5.2V P-P.
At 70Mhz, I got 6.8V P-P.
At 80Mhz, I got 7.6V P-P.
At 90Mhz, I got 4.7V P-P.
At 100Mhz, I got 2.7V P-P.

There is a big peaking at 80Mhz starting from 60Mhz, and fall off at 9xMhz at -3db. I don't think this qualifies for a 100MHz probe.

Any thoughts? Am I test it the wrong way?

Did you twist the input leads as recommended in manual?

[nctnico]

Perhaps the approx 15pf input capacitance of the scope is also an issue.

[boborich]

I did more testing and here are the findings:
1. Twisted the lead make things worse at 100MHz, now the P-P value drops more to 1.6V when twisted.
2. Tried to increase the signal output from 5V P-P to 10V P-P, same issue, no improvement.
3. Load the arb gen with 50ohm, the peaking seems better but still the same trend at 100MHz, drop to the toilit.
4. Try using seprate USB power to the probe, no change.
5. Tried on a different scope (DZ1054 hacked to 100MHz), same issue.

My conclusion is this probe is really usable at 50MHz with the standard leads....

BR,

Richard

[IAmBack]

It would be interesting to see this kind of test with probes from different manufacturer, like Tek.

[tautech]

I did more testing and here are the findings:
1. Twisted the lead make things worse at 100MHz, now the P-P value drops more to 1.6V when twisted.
2. Tried to increase the signal output from 5V P-P to 10V P-P, same issue, no improvement.
3. Load the arb gen with 50ohm, the peaking seems better but still the same trend at 100MHz, drop to the toilit.
4. Try using seprate USB power to the probe, no change.
5. Tried on a different scope (DZ1054 hacked to 100MHz), same issue.

My conclusion is this probe is really usable at 50MHz with the standard leads....

BR,

Richard

We don't know if this differential probe is affecting the integrity of the AWG sine waveform as we have no parallel reference for your measurements.

What I suggest is the SDG be set to HiZ output so that the signal amplitude matches that on its display (still 50 source) and a passive probe be also used as reference on another channel.

As the SDG BNC shells are mains ground referenced and so are the scope inputs this setup will compromise a truly differential measurement but still may offer some insights to accuracy...........or not.

[nctnico]

I did more testing and here are the findings:
1. Twisted the lead make things worse at 100MHz, now the P-P value drops more to 1.6V when twisted.
My conclusion is this probe is really usable at 50MHz with the standard leads....

Retest with a 50 Ohm termination (preferably on a scope with real 50 Ohm inputs).

[boborich]

Tried on the scope end with 50, 75, or 1M termination, doesn't affect the result, only the amplitude changes.

MDO3000 has internal termination selections. Definately neither the cause nor the solution to the bandwidth.

[capt bullshot]

It would be interesting to see this kind of test with probes from different manufacturer, like Tek.

Not exactly the same kind of test. Look at the attached waveforms:
Both were simultaneously acquired at the very same test point, a real world signal (gate drive to a power MOSFET)

Red trace is one of these: http://www.tek.com/isolated-measurement-systems (the 500MHz BW version), connected by the provided probe accessory to the DUT (coaxial cable, shield to MOSFET source, signal was run through a SMB connector soldered directly to PCB)

Blue trace is a Yokogawa branded 100MHz diff probe, with the two attached test leads clipped to the source and gate pin of the MOSFET

The ringing visible at the lead-out of the pulse is at 39MHz, well within the specified BW of the diff probe. BW limiting the tek probe to 250MHz didn't change a thing, next available BW limit was 20MHz, the ringing was gone (as expected).

As some of use were puzzled by this view (a reprensentative of Tek did a in-house demo of the Isovue probe), I verified the result by measuring the pulse using one of our old TPS2024 scopes (these have fully isolated inputs) - the same 39MHz ringng is visible with the same amplitude as the Isovue probe. Next I checked the BW of the diff probe using a signal generator. The result was quite the same as seen here by boborich, clearly related to the long input leads. Together with the input capacitance of the diff probe they form all kinds of antennas, resonant circuits and whatever, grossly varying the system (sig gen output impedance, leads, diff probe input impedance) frequency response above 50MHz.

So your usable BW of such kind of a diff probe heavily depends on the sources impedance and the test leads. For a defined frequency response above some 10s of MHz you'll have to use something like the Isovue probes.

[IAmBack]

I did more testing and here are the findings:
1. Twisted the lead make things worse at 100MHz, now the P-P value drops more to 1.6V when twisted.
My conclusion is this probe is really usable at 50MHz with the standard leads....

Retest with a 50 Ohm termination (preferably on a scope with real 50 Ohm inputs).

I think this probe is not intended to work with 50 Ohm input.

[IAmBack]

It would be interesting to see this kind of test with probes from different manufacturer, like Tek.

Not exactly the same kind of test. Look at the attached waveforms:
Both were simultaneously acquired at the very same test point, a real world signal (gate drive to a power MOSFET)

Red trace is one of these: http://www.tek.com/isolated-measurement-systems (the 500MHz BW version), connected by the provided probe accessory to the DUT (coaxial cable, shield to MOSFET source, signal was run through a SMB connector soldered directly to PCB)

Blue trace is a Yokogawa branded 100MHz diff probe, with the two attached test leads clipped to the source and gate pin of the MOSFET

The ringing visible at the lead-out of the pulse is at 39MHz, well within the specified BW of the diff probe. BW limiting the tek probe to 250MHz didn't change a thing, next available BW limit was 20MHz, the ringing was gone (as expected).

As some of use were puzzled by this view (a reprensentative of Tek did a in-house demo of the Isovue probe), I verified the result by measuring the pulse using one of our old TPS2024 scopes (these have fully isolated inputs) - the same 39MHz ringng is visible with the same amplitude as the Isovue probe. Next I checked the BW of the diff probe using a signal generator. The result was quite the same as seen here by boborich, clearly related to the long input leads. Together with the input capacitance of the diff probe they form all kinds of antennas, resonant circuits and whatever, grossly varying the system (sig gen output impedance, leads, diff probe input impedance) frequency response above 50MHz.

So your usable BW of such kind of a diff probe heavily depends on the sources impedance and the test leads. For a defined frequency response above some 10s of MHz you'll have to use something like the Isovue probes.

Thank You. This kind of behavior is expected with this kind of leads.

[Hydron]

I did some quick measurements using a spectrum analyser + tracking generator to check the bandwidth myself. Not the best setup, but I did normalise it first and terminated the tracking generator with 50R (and measured across that).

Twisted (tw prefix) vs untwisted (untw prefix) input wires had a large effect, and both had a big peak before they started dropping off. I'd ignore the low frequency wobbles - I know they're pretty flat below 10MHz from other measurements.

I think it shows that beyond 50MHz it's a bit of a crapshoot with leads that long. Fluke made a probe (DP120) with resistive co-ax input leads - I'd be interested to try one of those to see if it's damped by the input leads, though it's only 20MHz too, which would make things much easier to calm down.

I am going to mod one of my probes (the design of the gain selection and diff-SE conversion sections leaves a LOT to be desired, though the input buffer looks OK) in the future, so might look at shortening the leads at the same time. Will probably do another post about that if i get time on the weekend.

[alm]

I think it shows that beyond 50MHz it's a bit of a crapshoot with leads that long. Fluke made a probe (DP120) with resistive co-ax input leads - I'd be interested to try one of those to see if it's damped by the input leads, though it's only 20MHz too, which would make things much easier to calm down.

I have that probe (with Agilent branding). I recall having to twist the leads for it to meet its bandwidth (or CMRR?) specification while testing it. I pretty much permanently have the leads twisted except for the last 30 cm or so.

I am going to mod one of my probes (the design of the gain selection and diff-SE conversion sections leaves a LOT to be desired, though the input buffer looks OK) in the future, so might look at shortening the leads at the same time. Will probably do another post about that if i get time on the weekend.

I like the form factor Tektronix used with a long BNC cable and short flying leads much better. I guess the long flying leads are more convenient for portable operation (put the amplifier in a pocket/bag, or tape it to the portable scope) or use on large equipment, but on the bench much shorter leads would suffice.

[boborich]

Looking forward to your mod.

I did the same with a noise source (SDG2122x) and MDO3000's RF input, get the same result. But without a preamp, the dynamic range is.....

Thanks for the input.

[bitseeker]

I already got the HVP-70 before the Micsig came out. I do like having 10X rather than 50X. However, it's great to see more products coming out in the $100-200 price range since my scope still has three more channels available.

[nctnico]

Meanwhile I have got a MicSig DP10013 as well and had a short play with it.
I tried to use it on one of my products with a MOSFET push-pull stage to generate high voltage square waves. I measured the gate drive of the high-side MOSFET so one end of the probe is at the output signal and one at the gate.




Not bad but I would have liked to have less clunky test clips so it is easier to clip them on SMT transistors or chips (SOIC housing).

I did a comparison with one of my Pintek DP25 probes using my network analyser (twisted wires and 50x setting).

The Pintek DP25 terminated with 50 Ohm:


The Pintek DP25  terminated with 1M Ohm:


The MicSig DP10013 terminated with 50 Ohm:


The MicSig DP10013 terminated with 1M Ohm:


It is clear the DP10013 doesn't have a 100MHz bandwidth (at least when driven from a 50 Ohm source). When terminated with 50 Ohm it has a -3dB bandwidth of approx. 85MHz. OTOH compared to the much more expensive Pintek DP25 the MicSig DP10013 shows a much flatter frequency response.

[Micsig_support]

Anyone tested the bandwidth of the probe?
There is a big peaking at 80Mhz starting from 60Mhz, and fall off at 9xMhz at -3db. I don't think this qualifies for a 100MHz probe.

I've seen the same effect with some other 100MHz differential probe.
The root cause for this behaviour are the probes test leads, they are simply too long for a 100MHz bandwith. Try moving them around or twisting them, this heavily influences the frequency response above 60MHz.
IMO a diff probe claiming 100MHz BW but using such long test leads is just nonsense. The probe circuit itself would do a nice 100MHz -3dB rolloff, but using the non-removable leads spoils it all. Same thing as with the ground clip of an ordinary x10 probe, they tend to resonate around 100MHz.

His answer can explain your test result.

[CustomEngineerer]

Anyone tested the bandwidth of the probe?
There is a big peaking at 80Mhz starting from 60Mhz, and fall off at 9xMhz at -3db. I don't think this qualifies for a 100MHz probe.

I've seen the same effect with some other 100MHz differential probe.
The root cause for this behaviour are the probes test leads, they are simply too long for a 100MHz bandwith. Try moving them around or twisting them, this heavily influences the frequency response above 60MHz.
IMO a diff probe claiming 100MHz BW but using such long test leads is just nonsense. The probe circuit itself would do a nice 100MHz -3dB rolloff, but using the non-removable leads spoils it all. Same thing as with the ground clip of an ordinary x10 probe, they tend to resonate around 100MHz.

His answer can explain your test result.

So you are admitting that your probe as supplied can't actually meet the 100MHz specs? Why is it called a 100MHz probe then?

[David Hess]

So you are admitting that your probe as supplied can't actually meet the 100MHz specs? Why is it called a 100MHz probe then?

Technically the probe does have a -3dB bandwidth of 100 MHz when the leads are twisted just right.  It just also has 10dB of peaking and the horrible transient response to match making it only useful for measurements up to 40 MHz which coincidentally is about the bandwidth limit for honest probes.

It is called a 100 MHz probe because Micsig is lying.

[David Hess]

Fluke made a probe (DP120) with resistive co-ax input leads - I'd be interested to try one of those to see if it's damped by the input leads, though it's only 20MHz too, which would make things much easier to calm down.

Old differential probes worked this way using special calibrated x10 or x100 passive probes for the input leads and the fastest example I know of is 150 MHz.  Preamble, who was bought by LeCroy, makes a stand alone 100 MHz differential probe amplifier like this.

The lower performance high voltage differential probes are typically used for off-line switching applications where more than 20 to 40 MHz is not required anyway.  Instead of bandwidth think in terms of rise time.  50 MHz is 7 nanoseconds and how many power switches are faster than that?

Further, the common mode rejection of a high performance probe like the Preamble would not be sufficient in these applications anyway to take advantage of their 100 to 150 MHz bandwidth.  If you want to make high common mode rejection measurements with that kind of bandwidth, then a different method is required.

[VA]

it only useful for measurements up to 40 MHz which coincidentally is about the bandwidth limit for honest probes.

Give me a link to other "Honest" differential probe even 20MHz bandwidth(That's enough for me) with a price tag up to $120?

[David Hess]

it only useful for measurements up to 40 MHz which coincidentally is about the bandwidth limit for honest probes.

Give me a link to other "Honest" differential probe even 20MHz bandwidth(That's enough for me) with a price tag up to $120?

I do not know of any at that price unless you look to the used market.

[Jay_Diddy_B]

Hi,

I did some similar measurements with the Tektronix P5200 and the SI-9000A. These results were shared in this thread:



https://www.eevblog.com/forum/projects/high-voltage-differential-probe-design-for-review/msg595063/#msg595063

You have to be careful with the source impedance when making these measurements. This model shows that:



Here are the results of the three configurations. In the last configuration I am using different damping resistors:



This is just from the input divider and the lead inductance. You can see how lead inductance, would mess with the frequency response.

I have attached the LTspice model.

Regards,

Jay_Diddy_B

[Jay_Diddy_B]

Hi group,

This picture really illustrates one of the limitations of these probes, and a trap for young players:



The negative pulse on the Gate waveform s is probably not real. It there because the differential probe does not have enough common mode rejection ratio, to reject the large dv/dt impressed by the switching.

It is always best to place both probes on the switch node, Source of the top MOSFET, There should be no signal.

CMRR is often more important than BW.



Regards,

Jay_Diddy_B

[nctnico]

Ahum... you are pointing to the output signal and not the one measured by the differential probe. I should have written that in the desciption but then again over 90V gate drive voltage is a bit much for any MOSFET.

[David Hess]

You have to be careful with the source impedance when making these measurements.

For high voltage differential probes, I think there is an assumption based on the commonly intended application of off-line switching power supplies that the source impedances will be very low.

The negative pulse on the Gate waveform s is probably not real. It there because the differential probe does not have enough common mode rejection ratio, to reject the large dv/dt impressed by the switching.

It might be real and it might not.  I have seen that sort of gate waveform produced from a combination of high impedance from the gate driver and the dI/dT combined with the source inductance and dV/dT combined with the reverse transfer capacitance.

Note: nctnico cleared up that this is not showing the gate waveform but I have still seen gate waveforms that looked like that.

It is always best to place both probes on the switch node, Source of the top MOSFET, There should be no signal.

CMRR is often more important than BW.

I agree; the common mode rejection ratio is often more important than the bandwidth.

This test should always be done before trusting the differential probe with the measurement to find out if the common mode rejection ratio is sufficient.

[Janne]

About CMRR.. is it reasonable to assume that any of the cheap diff probes (sub 300$) will not be able do 60dB up to something like 100kHz? I'm thinkin of getting one to measure gate drive signals, but without good CMRR I would waste my money on a cheap probe and then would need to get a better one after that.

[David Hess]

About CMRR.. is it reasonable to assume that any of the cheap diff probes (sub 300$) will not be able do 60dB up to something like 100kHz? I'm thinkin of getting one to measure gate drive signals, but without good CMRR I would waste my money on a cheap probe and then would need to get a better one after that.

High voltage differential probes are all about equally poor at best under ideal conditions.  They should have a specification and hopefully a graph showing the minimum common mode rejection ratio versus frequency but this assumes the specifications can be trusted.  For the best common mode rejection, the source must be low impedance which common gate drive measurements should be.

If this is important, then the test described above will reveal if it is a problem and if it is, then some other measurement method will need to be used.

The big obscure complaint I have heard is that the common mode rejection ratio of cheap differential probes drifts which is not unexpected given their construction and of course there is no service documentation about adjusting it.  Older expensive high voltage differential probes spend more effort in the design and construction of just their front end attenuators than is applied to an entire cheap differential probe.  (1) I have tested the common mode rejection of my 20+ year old 100 MHz 7A13s and they are still spot on.

(1) If the attenuators are built on an FR4 type of substrate, then they are suspect.  This is very difficult to get right because of material and supplier problems no matter how good the design is.

[Macman]

About CMRR.. is it reasonable to assume that any of the cheap diff probes (sub 300$) will not be able do 60dB up to something like 100kHz? I'm thinkin of getting one to measure gate drive signals, but without good CMRR I would waste my money on a cheap probe and then would need to get a better one after that.

The spec sheet for the probe states a CMRR of >60DB at 100khz but I would be good idea to wait until someone can do a test to confirm the real world figures.

I have purchased a set of 2 in the Batterfly deal because they seemed such good value. My only comments so far is that I would have preferred if the probes had been  X10 and X100, also the output seems a bit noisy buy I don't think that is uncommon for a differential probe.

What I would really interested to see done is a detailed comparison between the performance of Dave's HVP70 probe and one of these Micsig probes.

[Jay_Diddy_B]

Hi,

You have to remember that a 500x probe is -53dB, so if the probe has a CMRR of 53dB at frequency x MHz, then differential and common mode signal appear the same size.

Example:

Tektronix P5200

Differential Gain



Common Mode Gain




Regards,

Jay_Diddy_B

[nctnico]

I did a measurement on the DP10013 I have with both inputs connected to the 50 Ohm output and the output of the probe terminated with 1M Ohm. I get -84dB from 10Khz to approx 1MHz and -70dB at 10MHz in 50x mode (34dB). So it seems the CMMR is 50dB up to 1MHz and 36dB at 10MHz.

[BravoV]

Just curious can we get "better" signal integrity at probing, if it is designed with standard female banana input like at DMMs ? Instead of two dangling long and loose wires.

I was thinking something looks like this (from those Pintech probe) ...


And then coupled with isolated banana to an "isolated" female BNC and maybe with a cheap 10X HV scope's probe (no exposed metal too).

[nctnico]

Those isolated banana adapters look neat! I'm thinking about modifying my MicSig diff. probe with an isolated BNC plug so I can attach a 'normal' probe to it or just solder a piece of coax (with isolated BNC) to the DUT.

[2N3055]

It can't be be coax.. It must be twisted pair.. Both cables are "equal" but different polarity. Same impedance, capacity.....
Also, coupled interference has to to be induced equally in both cables so amplifier can cancel it out.. If you put one to be on coax shield , it will get more coupling than one protected inside... You could do twisted pair with outside common shield.. 

[BravoV]

Those isolated banana adapters look neat! I'm thinking about modifying my MicSig diff. probe with an isolated BNC plug so I can attach a 'normal' probe to it or just solder a piece of coax (with isolated BNC) to the DUT.

It a genuine old Fluke/Philips banana to bnc adapters, bought them while ago when they were cheap at the bay  (posted here -> Philips BNC/Banana converter, but nowdays Aliexpress also carries clones now, though not sure about quality compared to genuine Philips one (as its also convertible into non shrouded banana). 

Regarding isolated BNC plug, I bought this (attached below) few months ago at Aliexpress too, saw it at the 1st time, and instantly ordered it even I didn't need it, yeah, hoarder nerves kicked in. 

[BravoV]

It can't be be coax.. It must be twisted pair.. Both cables are "equal" but different polarity. Same impedance, capacity.....
Also, coupled interference has to to be induced equally in both cables so amplifier can cancel it out.. If you put one to be on coax shield , it will get more coupling than one protected inside... You could do twisted pair with outside common shield..

Ok, noted, thanks. 

Well, my intention or at least expecting that with banana plug instead of fixed wires, we can improve the probe and cabling, say like using shorter cables, twisted cheap wires soldered on the test points, or using dual coax cables with both shield say connected to ground earth and etc.

My point is, with banana plug instead of fixed wires, it opens up the flexibility and variations at probing the HV test points.

[2N3055]

....
My point is, with banana plug instead of fixed wires, it opens up the flexibility and variations at probing the HV test points.

That is correct. I agree.

[toli]

Just noticed these probes a couple of days ago on Aliexpress, and and a quick google search brought me here obviously 

So what are the short term conclusion from these who own the probes? Do they seem to be reliable and worth the money? Or do they start coming apart/exhibit some sort of issues?

I understand there's a problem with the long leads and signals of ~40MHz and over. However, even with a 20MHz limit active on the scope, a 1300V differential probe for 160$ shipped is much cheaper than anything else you can get your hands on. Especially considering the fact it looks quite well designed and built.
Even with the X50 setting, and 130V max input, this can prove quite useful for genera use.

[BravoV]

The negative pulse on the Gate waveform s is probably not real. It there because the differential probe does not have enough common mode rejection ratio, to reject the large dv/dt impressed by the switching.

Is there an easy way to verify and remake a customized test in order to bring out this unwanted artifacts "intentionally" ?

I mean like say do the test using this diff. probe at certain test points or simple custom circuit, and then compared the result again at the same test points vs ordinary passive scope's probes. 

I guess the test points must has low enough (safer) voltage as we're going use common passive scope's probes.

Just a thought.

[David Hess]

Just curious can we get "better" signal integrity at probing, if it is designed with standard female banana input like at DMMs ? Instead of two dangling long and loose wires.

No.

The common mode rejection relies on balanced input impedances.  A single ended probe will just create a greater mismatch in impedance.  Low voltage differential probes can be used this way but only because they have much higher input impedance and are connected directly to the circuit without leads.  They rely on moving the probe as close as possible to the test points for their performance which includes not having input attenuators limiting them to low voltages.

What will work is two identical probes connected differentially which is how the old style high voltage differential probes worked.  They used special probes however which could be calibrated to match each other.  The simple leads on a modern high voltage differential probe are an attempt to make sure they match.

Common high voltage differential probes do *not* have a 1 megohm input resistance designed to work with single ended passive probes so the compensation will be all screwed up.  A special probe adapter that provides a 1 megohm load to the passive probe would be required unless a x1 probe was used.

Would a x1 probe work?  It would add a lot of differential and common mode capacitance.  I am dubious but try it and do the test below.

Is there an easy way to verify and remake a customized test in order to bring out this unwanted artifacts "intentionally" ?

Sure, this is easy.  Connect both leads of the differential probe to the same signal which has the large common mode voltage swing.  In an off-line switching power supply, this would usually be the emitter or source lead of the high side switch.  Since the leads are connected together, they see the same source impedance and zero volts between them.  Anything on the output represents the *best* possible results.  Real results when one lead is moved to the actual signal like the base or gate will be worse so if the best possible results are not good enough, the measurement will be corrupted.

When testing a low voltage active probe or a standard oscilloscope probe, the same test works.  Connect the probe tip to the same point as the ground lead.  Anything besides a flat trace that the oscilloscope shows represents the minimum error that a real signal will produce.

What level of common mode rejection is needed?  A typical off-line switching power supply operates with a peak-to-peak voltage of about 340 volts and a gate voltage of about 10 volts.  That comes out to about 31dB of common mode rejection for a completely corrupted measurement.  10% accuracy would require 51dB of common mode rejection.

An excellent high voltage differential probe can maintain 51dB (355:1) up to about 20 MHz or 17.5 nanoseconds which makes a 100 MHz specification ludicrous.

[Hydron]

I wouldn't say that 51dB CMRR @ 20MHz (well above what any of this type of probe will manage) is essential for them being useful - many circuits will be at mains potential but not at a high frequency potential (e.g. most parts of a PFC boost converter are referenced to the most-negative of the two mains input connections - this will move around a few hundred volts but at 50-60Hz, not in the 100s of kHz).

I do agree that measure the high side Vgs voltage of a high frequency converter will be difficult/impossible for this type of probe - even if the switching frequency is not high, the harmonics from the edge will make a huge mess of any measurement unless high frequency CMRR is very good. For the times I've had to do such measurements I've used a single channel of a battery powered PC-based scope controlled/connected over WiFi, but even with this you need to watch out for oddities due to parasitic capacitance to ground and inductance of the probe coax.

I'm not aware of high voltage diff-probes that do >50dB CMRR at 20MHz other than Tek's IsoVu or some niche products designed for this job (e.g. https://cleverscope.com/news/cs448/ ), and these are both in the $10k USD range (in the case of the Tek, up to $24k per channel!). Do you have examples of what probes you are thinking of?

On a different note, I did some rough checks of different cable lengths with the Micsig probe (temporarily added banana jacks to the probe to allow different length leads to be tested):
- The only way I have to do this is with a cheap spectrum analyser + tracking gen (normalised with a direct cable connection before measurement) so take these with a grain of salt.
- Only a single ended signal could be used as the input, so the -ve lead of the probe was at ground potential
- The tests were done at a 50 ohm input impedance, so 42dB attenuation is expected in 50x mode (=20log((50/(50+75))*(1/50))).
- At low frequencies there are also some measurement artifacts.
- Original probes best match the "medium" length (they are ~58cm plus whatever tip is selected).

The results show that the length of wire makes a large difference to frequency response, and in fact is relied upon for getting anywhere close to the rated bandwidth. Personally I'd be inclined to keep the original leads intact and treat them as 50MHz probes (potentially even mod them to roll off above this!), as while greater bandwidth is potentially possible, controlling peaking would be a nightmare as it depends strongly on physical arrangement of the leads (and probably more stuff too, e.g. source impedance, which was fixed at 50R for this test).

[David Hess]

I'm not aware of high voltage diff-probes that do >50dB CMRR at 20MHz other than Tek's IsoVu or some niche products designed for this job (e.g. https://cleverscope.com/news/cs448/ ), and these are both in the $10k USD range (in the case of the Tek, up to $24k per channel!). Do you have examples of what probes you are thinking of?

The older style ones which used adjustable passive probes could do it or come close if they are calibrated against the source impedance.  I think LeCroy is the only one that makes these now in the form of their DA1855A with one of their fully adjustable differential probe pairs.  The difference is that the probe pair has 8 calibration adjustments for each side and it has to be calibrated against both the differential amplifier and the source.

An oscilloscope with an isolated input is more cost effective and performs better if an unbalanced input impedance and low common mode input impedance is acceptable.  And that just leads back to floating the oscilloscope or preferably floating the device under test if an oscilloscope with isolated inputs or an isolated probe is not available.

Thanks for mentioning Cleverscope.  They make some great looking products.

[frozenfrogz]

Is this thing also usable for low voltage audio applications?
I guess the x50 gain is a bit to much and makes for a bad signal to noise ratio on low voltage circuits - or am I mistaken?
I am still such a bloody n00b in the field of measuring stuff correctly and precise :/

[jacklee]

I'm considering getting two of this probes recently, I thought I should get a discount from Micsig if I can buy two. 
I also saw this guy made a video for this scope, unfortunately, it seems in French language, so most of us would don't understand what he is talking.....
Micsig DP10013

[macboy]

Is this thing also usable for low voltage audio applications?
I guess the x50 gain is a bit to much and makes for a bad signal to noise ratio on low voltage circuits - or am I mistaken?
I am still such a bloody n00b in the field of measuring stuff correctly and precise :/

No, attenuation is too high for low voltage signals.
For low voltage audio frequency range stuff, you can build your own differential to single-ended converter with one or more op-amps (google instrumentation amplifier). With careful tweaking of resistors, you can get the common mode rejection to be very good.

[Hydron]

I'm using mine to look at stuff like gate drive signals (10s of volts swing), and half/full bridge outputs (100s of volts).
For low voltage stuff you might get some use with a sensitive scope (1mV/div or less) and bandwidth filtering to cut down on the noise, but it isn't really ideal.

I also did a quick test with a fast rise time 10MHz source, and could clearly see ringing at the ~70MHz frequency apparent in my earlier post (with the spec-an screenshots). This might be unavoidable with this style of probe (i.e. long leads and attenuation done in the probe body), and should be watched for. I might end up shortening mine so that the problem moves to a higher frequency.

[Pitrsek]

Those isolated banana adapters look neat! I'm thinking about modifying my MicSig diff. probe with an isolated BNC plug so I can attach a 'normal' probe to it or just solder a piece of coax (with isolated BNC) to the DUT.

Aviable as XF-SS/4 from Staubli/Multi contact - not cheap tough - cca 14eur.   

[Insatman]

I bought one of these on Ebay for $145 shipping included.  Seller was asking for $153 but came down just a bit.   Today I tested the rise time of the stock unit without any modification to the leads and using only the provided adapters for the shrouded banana input leads.  The test source is an avalance transistor pulser with a ~700ps Trise and relatively flat top squarewave.  The pulse shape was significantly distorted by the probe setup which is kinda expected as you are introducing a lot of stray capacitance.   Photos of the setup and waveforms are attached.  I may need two or three posts for all the photos.  Note that in the 50x mode I did at least get the promised 3.5ns Trise, although the pulse shape is an overall mess with a lot of ringing.   I'm guessing that usable bandwidth is significantly less and that improvement with shorter leads and better probe tips is possible.

[Insatman]

Next set of photos

[Insatman]

Final photo

[amham]

On sale at Mass drop:  $129.99

https://www.massdrop.com/buy/high-voltage-differential-probe-for-oscilloscope

[bitseeker]

Members-only, eh?

[BrianHG]

Cheapest ebay listing so far 142$:
https://www.ebay.com/itm/Micsig-Oscilloscope-1300V-100MHz-High-Voltage-Differential-Probe-kit-DP10013/282812242682?_trkparms=aid%3D555017%26algo%3DPL.CASSINI%26ao%3D1%26asc%3D20170810094027%26meid%3D94a2bc9a0164464bbc740d7479f9cc57%26pid%3D100855%26rk%3D1%26rkt%3D1%26%26itm%3D282812242682&_trksid=p2349526.c100855.m4779

[Ghislain]

I'm considering getting two of this probes recently, I thought I should get a discount from Micsig if I can buy two. 
I also saw this guy made a video for this scope, unfortunately, it seems in French language, so most of us would don't understand what he is talking.....
Micsig DP10013

I have made a short summary of the most important topics that are being explained, please note I am sticking as closely as possible to what is being said.
Reference video time indications are put in [ ] for easier reference.

1. Introduction
Probe was procured via Banggood and was considered as not being expensive

2. Unboxing [1:00]
Good quality box
Details on the content of the box

3. Closer look at the probe [2:20]
Two flexible input leads however not silicone, quality assessment 'rather good'
USB input (power) and one output
Detailed description of the contents of the leaflet [4:29]
Question raised on CMV (1300V) vs Max Input V to earth (1000V)
Measured current consumption about 200 mA

4. Tests
Considerable noise level, probe needed calibration (procedure is explained in the leaflet) [10:50]
CMRR 50Hz/10MHz sinus with max 20V P2P from a Rigol generator [12:10]
Sensitivity: acceptable for high tension measurements [15:00]
Linearity: green trace on oscilloscope is output generator, yellow trace output probe [16:50], as of 5 MHz slight out of phase noticeable [18:40]
Bandwidth: not really linear, logaritmic view shows a flat response up to about 10MHz [22:40], remark: test conditions suboptimal because of equipment limitations
Mains connected to Siglent 1202X-E, probe X500 [23:25]
Connected to (defective?) switched PSU [25:13]
Safety warning when working with high tension (test setup is not safe!) [26:20]
Internals of the probe [27:35]

5. Conclusion
The probe has its limitations but does a good job [28:50] 

[bitwelder]

Cheapest ebay listing so far 142$:
https://www.ebay.com/itm/Micsig-Oscilloscope-1300V-100MHz-High-Voltage-Differential-Probe-kit-DP10013/282812242682?_trkparms=aid%3D555017%26algo%3DPL.CASSINI%26ao%3D1%26asc%3D20170810094027%26meid%3D94a2bc9a0164464bbc740d7479f9cc57%26pid%3D100855%26rk%3D1%26rkt%3D1%26%26itm%3D282812242682&_trksid=p2349526.c100855.m4779

Looking at it from here, the USD 142 are about EUR 115.
In that case I see a few Chinese/Malaysian sellers offering it at EUR 108.30 (plus minimum 1.50 for shipping), but it seems that the offer is valid only for most of Europe.

BTW, do you see a significant difference or risk between buying directly from Micsig Aliexpress store, or from Banggood, or from some well-established eBay seller?

[17_29bis]

I own a DP10013 and wonder how the following can be explained.

The probe input resistance/capacitance is 10M / 1pF (in diff mode),  I am checking the voltage on the CCFL  connected to the 21" monitor power supply AIP-0121 (it powers  4 CCFL).

I know that this particular size of CCFL  runs at 700V(normal mode) - 1400V (start) Volts and draws about 4-8 mA (the frequency is about 62kHz). It is easy to calculate the equivalent resistance of the  CCFL which is about 150K -200K.

But when I connect the probes of DP10013 to CCFL connector, in a second or so the power supply turns off (due to internal protection) and works just fine if no probe is connected.

During that second I still can capture enough info to see the signal form etc  but I am just curious why the probe affects the work of the power supply - it has much higher resistance and much lower capacitance to make any different but nevertheless it does.

What am I missing here?

Thanks!

[BillB]

Cheapest ebay listing so far 142$:
https://www.ebay.com/itm/Micsig-Oscilloscope-1300V-100MHz-High-Voltage-Differential-Probe-kit-DP10013/282812242682?_trkparms=aid%3D555017%26algo%3DPL.CASSINI%26ao%3D1%26asc%3D20170810094027%26meid%3D94a2bc9a0164464bbc740d7479f9cc57%26pid%3D100855%26rk%3D1%26rkt%3D1%26%26itm%3D282812242682&_trksid=p2349526.c100855.m4779

Looking at it from here, the USD 142 are about EUR 115.
In that case I see a few Chinese/Malaysian sellers offering it at EUR 108.30 (plus minimum 1.50 for shipping), but it seems that the offer is valid only for most of Europe.

BTW, do you see a significant difference or risk between buying directly from Micsig Aliexpress store, or from Banggood, or from some well-established eBay seller?

I picked one up from a different seller on eBay who was willing to negotiate. 

It took a while to show up, but it works fine.  I think the risk is low buying from a proven eBay seller, and most likely, it's probably the same people selling the same stuff on the other sites.

[nctnico]

I own a DP10013 and wonder how the following can be explained.

The probe input resistance/capacitance is 10M / 1pF (in diff mode),  I am checking the voltage on the CCFL  connected to the 21" monitor power supply AIP-0121 (it powers  4 CCFL).

I know that this particular size of CCFL  runs at 700V(normal mode) - 1400V (start) Volts and draws about 4-8 mA (the frequency is about 62kHz). It is easy to calculate the equivalent resistance of the  CCFL which is about 150K -200K.

What am I missing here?

The total load of the probe and wires is likely several pf which at 700V and 62kHz can easely draw a mA extra.

[17_29bis]

The total load of the probe and wires is likely several pf which at 700V and 62kHz can easely draw a mA extra.

I totally understand that. And most likely this is true, because the active resistance of the probe should not affect the work of the inverter much (see the calculations above).

On the other hand if the capacitance of the wires (non-replaceable btw i.e you should use what you have, I twisted them as was suggested), and I am speaking about the wires only because  if the documentation is correct then we can probably neglect 1pF capacitance of the probe, in several times bigger than 1pF then that is kind of strange because all that narrows the application area of this particular probe.

[tautech]

The total load of the probe and wires is likely several pf which at 700V and 62kHz can easely draw a mA extra.

I totally understand that. And most likely this is true, because the active resistance of the probe should not affect the work of the inverter much (see the calculations above).

On the other hand if the capacitance of the wires (non-replaceable btw i.e you should use what you have, I twisted them as was suggested), and I am speaking about the wires only because  if the documentation is correct then we can probably neglect 1pF capacitance of the probe, in several times bigger than 1pF then that is kind of strange because all that narrows the application area of this particular probe.

Consider that low value caps can be made by twisting wires together. If the inverter is that sensitive and running close to it's trip point....... well you get the picture. 
Every measurement affects a circuit !

[nctnico]

The total load of the probe and wires is likely several pf which at 700V and 62kHz can easely draw a mA extra.

I totally understand that. And most likely this is true, because the active resistance of the probe should not affect the work of the inverter much (see the calculations above).

On the other hand if the capacitance of the wires (non-replaceable btw i.e you should use what you have, I twisted them as was suggested), and I am speaking about the wires only because  if the documentation is correct then we can probably neglect 1pF capacitance of the probe, in several times bigger than 1pF then that is kind of strange because all that narrows the application area of this particular probe.

IMHO a high voltage 1:100 probe is more suitable for this kind of measurement since one side of the inverter output and CFL is likely tied to ground anyway.

[17_29bis]

IMHO a high voltage 1:100 probe is more suitable for this kind of measurement since one side of the inverter output and CFL is likely tied to ground anyway.

That's true, although I don't have schematics for this particular inverter but I think one side of each CCFL is connected to the ground. And speaking about  high voltage 1:100 passive probes. Yes, fancy ones from Tektronix will have low capacitance (4pF for 300$ USD / 2.5pF for 470$USD / 1.8pF for 840$ USD),  cheap ones (20$-50$) will have capacitance is double digits. Knowing that this is why I bought DP10013 with its 1pF for 180$  in the first place. But anyway thanks for the input.

Consider that low value caps can be made by twisting wires together. If the inverter is that sensitive and running close to it's trip point....... well you get the picture. 

Somehow I thought that parallel wires have the biggest capacitance. Anyway, thanks for the hint, will try to untwist the wires and see what happens.

[Mechatrommer]

I own a DP10013 and wonder how the following can be explained.

The probe input resistance/capacitance is 10M / 1pF (in diff mode),  I am checking the voltage on the CCFL  connected to the 21" monitor power supply AIP-0121 (it powers  4 CCFL).

I know that this particular size of CCFL  runs at 700V(normal mode) - 1400V (start) Volts and draws about 4-8 mA (the frequency is about 62kHz). It is easy to calculate the equivalent resistance of the  CCFL which is about 150K -200K.

What am I missing here?

The total load of the probe and wires is likely several pf which at 700V and 62kHz can easely draw a mA extra.

the probe is a single wire. its not like coax which has surrounded gnd wires which contribute to high capacitance. i suspect the probed voltage exceed the diff probe common mode. it also can be due to high transient that capacitors paralleled across 5MOhm divider got into short circuit creating low impedance path. but i could be wrong.

IMHO a high voltage 1:100 probe is more suitable for this kind of measurement since one side of the inverter output and CFL is likely tied to ground anyway.

i dont find it relevant or rational. one should be fine with 1:50 (or 1:10 etc) probe as long as its working in its commong mode range.

[Dwaine]

I have one coming.  Has anyone confirmed if there really is different firmwares.

[PedroDaGr8]

Just purchased one for $113.60 (EBay has a 20% off coupon code, that the sellers haven't adjusted to yet!). Looking forward to using it on a few projects!

[Mr. Scram]

No, attenuation is too high for low voltage signals.
For low voltage audio frequency range stuff, you can build your own differential to single-ended converter with one or more op-amps (google instrumentation amplifier). With careful tweaking of resistors, you can get the common mode rejection to be very good.

What would be considered low voltage signals in this context?

[nctnico]

No, attenuation is too high for low voltage signals.
For low voltage audio frequency range stuff, you can build your own differential to single-ended converter with one or more op-amps (google instrumentation amplifier). With careful tweaking of resistors, you can get the common mode rejection to be very good.

What would be considered low voltage signals in this context?

Less than +/-10V. I've built such a differential amplifier myself using a differential amplifier from Analog devices. It is powered by +/-15V which gives a permitted input range and output swing about +/-12V.

[tautech]

No, attenuation is too high for low voltage signals.
For low voltage audio frequency range stuff, you can build your own differential to single-ended converter with one or more op-amps (google instrumentation amplifier). With careful tweaking of resistors, you can get the common mode rejection to be very good.

What would be considered low voltage signals in this context?

It depends a little on the input sensitivity of your scope.

A 1000:1 HV passive probe I got recently can easily resolve the scope 3V compensation signal and allow probe compensation adjustments, no problem.

[David Hess]

What would be considered low voltage signals in this context?

Low voltage differential amplifiers have no input attenuation.  For the best ones, this limits their input common mode and differential input range to about +/-10 volts although conceivably a good design could extend that a few times at the expense of bandwidth.

[stenbror]

I just bought two MicSig 100Mhz Differential probes from Banggood for under 300 dollars. (NOK 2620) including delivering in about 17days from China straight to my mailbox in Norway without any import fees. Yes......

[tsman]

Micsig have added a new model. DP20003 which is 100MHz still but 200x + 2000x instead of 50x + 500x.

[edit]Corrected mistake. 150 -> 50 and 1500 -> 500[/edit]

[CustomEngineerer]

The DP10013 (assuming this is the one you are referring to at least) is 50x/500x, not 150x/1500x.

[tsman]

The DP10013 (assuming this is the one you are referring to at least) is 50x/500x, not 150x/1500x.

Oops. Yes. Not sure where that extra 1 sneaked in from.

[slloyd]

i have two of these probes.  on x50 scale and both on the probe compensation terminals of RTM3004 350MHz scope.  it shows an offset between the two measurements.  to calibrate the probe, i have to open the case and adjust the multiturn pot?

[Hydron]

A DC offset can be nulled by shorting the inputs together and then holding both range buttons down until it starts clicking and flashing the lights.

I would be very interested to see inside the 200x/2000x version if anyone gets one (unfortunately it's annoying to get inside, have to carefully peel up the front sticker, though it's possible to do it without damage).

Edit: I'd also be interested in the frequency response of the new version - it seems to have even longer leads, and the old one already has issues where they can ring (due to L and C of the fairly long leads) within the claimed 100MHz bandwidth.

[tsman]

I'd also be interested in the frequency response of the new version - it seems to have even longer leads, and the old one already has issues where they can ring (due to L and C of the fairly long leads) within the claimed 100MHz bandwidth.

Same length leads. The DP20003 photo is just bigger. The specifications say ~60cm for both of them.

[lordvader88]

So what's the pro's/con's of these for someone that could afford these but not +400 ? I have a hard time saving money without spending it

People have had them for a while, what are they like ?

[Mr. Scram]

Micsig have added a new model. DP20003 which is 100MHz still but 200x + 2000x instead of 50x + 500x.

[edit]Corrected mistake. 150 -> 50 and 1500 -> 500[/edit]

That's quite nice, though the spelling errors on the official page don't instill much confidence.

[nctnico]

Micsig have added a new model. DP20003 which is 100MHz still but 200x + 2000x instead of 50x + 500x.

[edit]Corrected mistake. 150 -> 50 and 1500 -> 500[/edit]

That's quite nice, though the spelling errors on the official page don't instill much confidence.

Learn Chinese then 

[Mr. Scram]

Learn Chinese then 

I'd never comment on an individual making an effort, but this is a proper business.

[nctnico]

Learn Chinese then 

I'd never comment on an individual making an effort, but this is a proper business.

Still in many countries it is extremely hard to find someone who knows how to speak/write decent English. It is not a given everybody on earth can understand English.

[Mr. Scram]

Still in many countries it is extremely hard to find someone who knows how to speak/write decent English. It is not a given everybody on earth can understand English.

I don't think a competent Chinese to English translator would be hard to find for pretty much anyone with internet access. This is a legitimate business, not a Tindie shop.

[nctnico]

Still in many countries it is extremely hard to find someone who knows how to speak/write decent English. It is not a given everybody on earth can understand English.

I don't think a competent Chinese to English translator would be hard to find for pretty much anyone with internet access. This is a legitimate business, not a Tindie shop.

But as a customer who can't understand English: how do you know the translator is any good? After all In the land of the blind, the one-eyed man is king and given the amount of Chinglish we are subjected to the Chinese translators aren't afraid to oversell themselves. All in all it is foolish to dismiss a company because their foreign language website has some spelling / grammer errors.

[GreyWoolfe]

Still in many countries it is extremely hard to find someone who knows how to speak/write decent English.

Unfortunately, it is just as hard here in the US.

[Mr. Scram]

But as a customer who can't understand English: how do you know the translator is any good? After all In the land of the blind, the one-eyed man is king and given the amount of Chinglish we are subjected to the Chinese translators aren't afraid to oversell themselves. All in all it is foolish to dismiss a company because their foreign language website has some spelling / grammer errors.

You know a translation is good if you've hired a proper translator. There are various translators who specialise in the Anglo-Chinese market that can provide a decent a high quality translation for a modest fee. It can hardly be the first text that Micsig requires to be translated, so I'd expect them to have some experience with translators at this point. Even if just for foreign official documents.

I guess that you don't get it if you don't get it. I'm not nearly dismissing a company because of spelling errors. It does however reflect badly on the quality of the product and how one does business. In this case it's even a safety critical product. Some people might be tempted to wonder where else they cut corners. If you spend tens of thousands of dollars on the development and certification of a product and go through some effort to set up a decent website it's painful to drop the ball with the finish line in sight. That also applies to the Chinglish in device menus, by the way. Paying next to nothing for a proper translation is how a company can separate itself from all the hopefuls that occupy the lower tiers of the market. You can bet the Keysights and Flukes get their texts translated by very capable translators.

If you don't get it you don't get it, but a little goes a long way. That's all.

[Hydron]

...so I finally got around to cutting off ~20cm of lead length on one my DP10013 probes. I haven't done any proper measurements of the new frequency response after the mod, but it sure did make an improvement regarding ringing!
The attached pic shows 3 different probes measuring the same signal, yellow is a (decent) 300MHz 100:1 passive probe, green is the modified DP10013, and orange is the un-modified DP10013. Ignoring the skew between the signals, the modded Micsig is much closer to the passive reference probe (which here I am regarding as being a lot more likely to represent the true signal).
Time permitting I'll try and check out the frequency response of the modded vs original probe, but given what I've seen so far I suspect I'll be doing the same change to the other one of the pair I bought.

Note: both diff probes had their leads twisted together. Results would be different if not doing this - unfortunately it makes a fairly big change in their response.

[mk_]

...so I finally got around to cutting off ~20cm of lead length on one my DP10013 probes. I haven't done any proper measurements of the new frequency response after the mod, but it sure did make an improvement regarding ringing!

It is a well known secret that leads for oscilloscope-probes should be "resistive" wires for damping ringing. There is an old AN from Tektronix somewhere on the net which demostrates this. In the - also old - AN called "TekProbeCircuits" you can see some resistor in the signalpath for damping this ringing (Rs on p18, Fig. 2-10)

[Hydron]

Yes agreed - this (combined with the longer than usual length) is why some people including myself earlier in the thread were dubious about the design before anyone even did any measurements. But the price was right (even for the more accurate ~50MHz of bandwidth you get without the lead peaking) so I went for a couple anyway.

This issue is certainly not confined to the Micsig probe - most models of differential probe in this style have non-resistive leads, and I suspect the only reason they get away with it is that their response doesn't reach high enough to see the undamped ringing. There is a certain discontinued fluke model (DP-120?) that has resistive input leads forming part of the attenuation circuit but sadly it is limited to a fairly low 20MHz bandwidth.

[mk_]

Yes agreed - this (combined with the longer than usual length) is why some people including myself earlier in the thread were dubious about the design before anyone even did any measurements. But the price was right (even for the more accurate ~50MHz of bandwidth you get without the lead peaking) so I went for a couple anyway.

This issue is certainly not confined to the Micsig probe - most models of differential probe in this style have non-resistive leads, and I suspect the only reason they get away with it is that their response doesn't reach high enough to see the undamped ringing. There is a certain discontinued fluke model (DP-120?) that has resistive input leads forming part of the attenuation circuit but sadly it is limited to a fairly low 20MHz bandwidth.

Switching from 0 to 600V in 30-40ns results in a lot of ringing with the original leads at my Testec SI 9110 (1:100(0), 100Mhz, 1,4kV)  so I replaced those leads with some from a broken Tek. It`s a filigrane construction but anyway... bandwith remaind the same but no more ringing.

[nctnico]

From my own measurements it seems that the DP10013 works best with the original lead lengths. I assume MicSig factored in the capacitance between the leads (when twisted) into the frequency response.

[SteveyG]

I missed this thread 

I posted a video recently about this differential probe and will be using it in some upcoming videos, but I did want to comment that having used this on my bench for the past week or so it actually works really well and in my opinion can't be beaten in terms of value for money.

https://www.banggood.com/custlink/33G3Jmr8bC
Coupon code: "aff7off" brings it down to around £120 delivered, which IMO is a bargain

Here's my video if anyone is interested:
https://youtu.be/dzeK3Nm3N44

[frozenfrogz]

You do not need to go through the trouble of importing from China. Buy via ebay.co.uk from Germany for less than £100 delivered.

[SteveyG]

Doesn't show up for me anything like that on ebay for the UK. Thanks for the info though 

[frozenfrogz]

Doesn't show up for me anything like that on ebay for the UK. Thanks for the info though 

https://www.ebay.co.uk/itm/New-1300V-Oscilloscope-100MHz-Differential-Probe-Kit-Micsig-DP10013-EL/143093519228

Postage from UK

[SteveyG]

They're a bit naughty with the listing, it's being shipped from Singapore to the UK warehouse then on to you to avoid customs charges.

[frozenfrogz]

They're a bit naughty with the listing, it's being shipped from Singapore to the UK warehouse then on to you to avoid customs charges.

Well sure, this was just the first listing I found, when switching my "location" to UK. Anyway, all those devices somehow have to make their way from China to the EU (or thereabout xD) and as long as the seller takes care of that, it is fine with me - it is still 110 € delivered without having to deal with DHL Express / customs / ...
I have been prancing around one of these for quite some time and now seems a good time to finally buy one - thanks for reminding me.

Edit: On ebay.de there are a bunch of listings from the same seller. Same price, but the listing quotes "DP10013 EDQ", "DP10013 LY", "DP10013 EAv",... Are these just identifiers from the seller per listing or are there several different versions available? I am a bit confused. Micsig website does not help here. 

[SteveyG]

They're a bit naughty with the listing, it's being shipped from Singapore to the UK warehouse then on to you to avoid customs charges.

Well sure, this was just the first listing I found, when switching my "location" to UK. Anyway, all those devices somehow have to make their way from China to the EU (or thereabout xD) and as long as the seller takes care of that, it is fine with me - it is still 110 € delivered without having to deal with DHL Express / customs / ...
I have been prancing around one of these for quite some time and now seems a good time to finally buy one - thanks for reminding me.

Edit: On ebay.de there are a bunch of listings from the same seller. Same price, but the listing quotes "DP10013 EDQ", "DP10013 LY", "DP10013 EAv",... Are these just identifiers from the seller per listing or are there several different versions available? I am a bit confused. Micsig website does not help here.

I think those are nothing to do with the part numbers, just some weird thing the person listing it is doing. I quite like using Banggood as they also deal with the import duty and actually sort out any problems with an order.

[MiroS]

I quite like using Banggood as they also deal with the import duty and actually sort out any problems with an order.

I do not think that this 'like'  can justify 30 USD more  or so   Especially that this maybe 30 usd more on  top of custom  and VAT.

[Housedad]

I'm going to try adding resistors to the leads and see what happens with my MSIG probe.  I was reading about this on the Keysight paper http://literature.cdn.keysight.com/litweb/pdf/5992-2848EN.pdf  Starting on page 8.

[joesmith]

I missed this thread 

I posted a video recently about this differential probe and will be using it in some upcoming videos, but I did want to comment that having used this on my bench for the past week or so it actually works really well and in my opinion can't be beaten in terms of value for money.

https://www.banggood.com/custlink/33G3Jmr8bC
Coupon code: "aff7off" brings it down to around £120 delivered, which IMO is a bargain

Here's my video if anyone is interested:
https://youtu.be/dzeK3Nm3N44

This looks really nice

[exe]

I quite like using Banggood as they also deal with the import duty and actually sort out any problems with an order.

Are you sure about this? Last time I used banggood (about 2 years ago or so) it was explicitly mentioned that import tax and duties are on the buyer. They even used to have "tariff insurance": https://blog.banggood.com/banggood-tariff-insurance-61604.html .Also, I see they say explicitly on their website that they do not manager import taxes and duties: https://www.banggood.com/Taxes-and-tariffs_hl69_at310

[SteveyG]

I quite like using Banggood as they also deal with the import duty and actually sort out any problems with an order.

Are you sure about this? Last time I used banggood (about 2 years ago or so) it was explicitly mentioned that import tax and duties are on the buyer. They even used to have "tariff insurance": https://blog.banggood.com/banggood-tariff-insurance-61604.html .Also, I see they say explicitly on their website that they do not manager import taxes and duties: https://www.banggood.com/Taxes-and-tariffs_hl69_at310

Any order over the duty threshold with the insurance appears to go to a warehouse just near Heathrow Airport, and is then delivered by Yodel as a UK shipment. They have to put the warning on the website though I would assume.

If you use the link: https://www.banggood.com/custlink/33G3Jmr8bC Banggood have offered the discount code "DP10013" to drop the price to $139.99 delivered.

[BravoV]

If you use the link: https://www.banggood.com/custlink/33G3Jmr8bC Banggood have offered the discount code "DP10013" to drop the price to $139.99 delivered.

Actually you can get < $130 s/h included at Aliexpress with shop that sold many of it with good many feedbacks too, just fyi.

[SteveyG]

If anyone is interested, you can see the innards of the DP20003 in this short video. Micsig have increased the quality of the accessories in all new models so worth checking if it's new stock if you happen to order:

[mnsergey]

Today came to me the same, only high-voltage DP20003 from the company Micsig. Multipliers X200 and X2000 and maximum voltages, respectively 560V / 5600V. Quickly checked parameters give Rice Time ~ 10nS (against the stated 3.5 nS) and a frequency range of up to 25MHz on the AFC drop (-3dB) (against the stated 100MHz). So the Chinese are lying, the real delay is three times worse than the stated Rise Time parameter.
And this does not seem to be an isolated case, but a a deceptive business put on stream.
Just a week ago I'm received from  a current probe of the upper model Micsig CP2100B(2.5 MHz/175nsec) at a price of ~ $ 360. Promised a delay of less than 175nsec. As a result, after the tests, I got a delay of more than 450nsec, which is in fact the Junior CP2100A model with a price of about $165.
In the last case, a dispute was opened with the seller, and the device had to be sent to China as not meeting the stated parameters.
To say that I am angry, -  is  say nothing.
All such stories happen in the world, dear community...

[TopLoser]

Today came to me the same, only high-voltage DP20003 from the company Micsig. Multipliers X200 and X2000 and maximum voltages, respectively 560V / 5600V. Quickly checked parameters give Rice Time ~ 10nS (against the stated 3.5 nS) and a frequency range of up to 25MHz on the AFC drop (-3dB) (against the stated 100MHz). So the Chinese are lying, the real delay is three times worse than the stated Rise Time parameter.

I'm pretty sure people are going to suggest the probing setup in your photo is going to need a bit of improvement to show those kind of risetimes...

[TK]

Try twisting the red and black wires several turns and see if it improves the signal rise time

[briangordon]

I'm kind of concerned about powering it via the oscilloscope's USB port. I assume that the USB port on the scope is going to be tied to chassis ground and the USB power is going to be referenced to that as well. So is it really safe to measure a DUT that's powered by mains? Is the micsig probe's power input sufficiently isolated for this?

[2N3055]

I'm kind of concerned about powering it via the oscilloscope's USB port. I assume that the USB port on the scope is going to be tied to chassis ground and the USB power is going to be referenced to that as well. So is it really safe to measure a DUT that's powered by mains? Is the micsig probe's power input sufficiently isolated for this?

BNC output is allready connected to scope ground. Actually it is how it works in these types of probes. You have two inputs, both referenced to scope ground and you measure difference between them and convert it to single ended output.
Inputs are not floating with infinite resistance towards ground. They both have some high impedance path to ground, specified in manual.

[boB]

Old and ongoing thread, I know...

We have several of these Micsig differential probes (50X  500X) and  a lot of them eventually develop a DC offset.   You are supposed to be able to calibrate out this offset by holding down the 50X  and  500X  buttons for a moment while having the input leads shorted together.    This never works, at last for the sometimes large offset that we see.  I think the little processor may do the offset-null by injecting another offset into the last op-amp circuit...

I like Dave's video on this but however this works is left for the viewer to finish. 

I wonder if anyone here has ran into this issue and what you did to fix it ?

Thanks,
boB

[2N3055]

Old and ongoing thread, I know...

We have several of these Micsig differential probes (50X  500X) and  a lot of them eventually develop a DC offset.   You are supposed to be able to calibrate out this offset by holding down the 50X  and  500X  buttons for a moment while having the input leads shorted together.    This never works, at last for the sometimes large offset that we see.  I think the little processor may do the offset-null by injecting another offset into the last op-amp circuit...

I like Dave's video on this but however this works is left for the viewer to finish. 

I wonder if anyone here has ran into this issue and what you did to fix it ?

Thanks,
boB

That is interesting. Would you mind elaborating how much of the offset we are talking about here?
Thanks!

[Hydron]

Yep, had the same issue with one of mine, just started doing it when I got it out of the drawer one day. Annoyingly it's the one that I did some hacking on (shortened the leads to get rid of some peaking) so no chance of a RMA, even if it were within warranty.

I did a bit of a bodge to improve it by figuring out how the offset circuit worked and padding one of the reference resistors. Can't remember much more detail than that but very annoying to have to do this - given others have the same problem would no longer recommend these even given the cheap price.

[EEVblog]

FYI, just got in new stock of my HVP70 probe.

[boB]

Yep, had the same issue with one of mine, just started doing it when I got it out of the drawer one day. Annoyingly it's the one that I did some hacking on (shortened the leads to get rid of some peaking) so no chance of a RMA, even if it were within warranty.

I did a bit of a bodge to improve it by figuring out how the offset circuit worked and padding one of the reference resistors. Can't remember much more detail than that but very annoying to have to do this - given others have the same problem would no longer recommend these even given the cheap price.

Interesting !   Did you find that the micro added in the anti-offset into that 3rd and final op-amp ?

I was trying to add on to the Dave-Cad schematic but the one that I was just working on appears to be slightly different.  For instance, the main differential amplifiers are in a single chip.  Then the 3rd op-amp  appears to be a dual OPMI labeled TI amp.  AND, I cannot seem to trace the 50 Ohm output to that 3rd op-amp.  Not in the short amount of time I spent on it anyway.

Answer to the question, how much offset...  It varies.  On this latest probe, changing the 500X to 50X does not appear to change the absolute output offset.   The probe is still useful though.  Just have to offset the scope and try to remember where zero is if I am measuring DC.
It also can be worse and maybe even better at different times when letting it sit.   But it is always enough to be annoying.

 I think that it is offset enough where the processor cannot quite put it right again.

Dave, is your  HVP70 probe  the one with 100X that you showed in your video ?    That is a nice compromise.  Hopefully they have gotten the CMR fixed as promised.

boB

[2N3055]

Still nobody mentions any numbers... How much offset do you people see?

[boB]

I will measure it again and give the absolute number.  I can't remember.

The power supply for the op-amps is basically +/- 9.x volts

[Hydron]

Enough to be very annoying for sure, cannot remember though and like I said I've mostly fixed it.

[boB]

I measure it today and the absolute output offset is only  +50 mV

At 500X, this turns out to be + 25V offset so if I could just calibrate this offset out of the scope itself (Rigol) that would
be OK. 

At +/-  9V op-amp supply, this should still work OK for most things.

Still annoying but now that I know there is that little isolated supply powers things with a lot more than just +5V, it's not all that bad.

The schematic for this particular DP10013_V3X  2017.11.10  is somewhat different than the most recent Dave-Cad version though with the single input stage opamps.   For instance, the output R of 50 Ohms is about 1 K Ohm or more away from any of the third dual op-amp output pins so I don't understand that.

Just checked another DP10013 and it HAD +50mV or so but calibrated down to about +2 mV.

PS...   NOW if I could only find the point where the micro normally injects its offset, I could make it work OK.

Actually, I suppose I could just add a trimpot circuit into that 3rd differential op-amp circuit.  I should probably figure out why I am seeing >1K Ohm between main probe output and that op-amp though.

boB

[Hydron]

Had a chance to look inside the probe I fixed and took a pic of the resistor padding I had to install. Can't find the reverse engineered schematic I drew sorry!
Fix seems to work well - am getting a sub-millivolt offset (before multiplication factor), but it looks like I had to use a few resistors to do it, in 2 places.

Attachments are the fix, plus front/back of the board I have (pre-fix).

[2N3055]

I just tested mine.

They generally have arround  100uV of nonscaled offset and arround 500uV RMS of noise (with 20MHz limiter on scope) at 50X.
At 500X they have arround  100uV of nonscaled offset and arround 180uV RMS of noise (with 20MHz limiter on scope)

That is nonscaled for probe factor.

[boB]

Had a chance to look inside the probe I fixed and took a pic of the resistor padding I had to install. Can't find the reverse engineered schematic I drew sorry!
Fix seems to work well - am getting a sub-millivolt offset (before multiplication factor), but it looks like I had to use a few resistors to do it, in 2 places.

Attachments are the fix, plus front/back of the board I have (pre-fix).

Thanks !

So you changed R60 and R64 to fix the offset ?

Not sure what's been done on the back of the PCB but will ZOOM in

boB