Author Topic: Where can I find inexpensive differential probes?  (Read 29196 times)

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Offline nbrittonTopic starter

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Where can I find inexpensive differential probes?
« on: October 26, 2015, 04:52:35 am »
Where can I find inexpensive differential probes? I have a four channel scope and I'd like to probe across four individual components in circuit so that I can study their properties for educational purposes. I don't need anything fancy or high voltage or high bandwidth.
 

Offline eas

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Re: Where can I find inexpensive differential probes?
« Reply #1 on: October 26, 2015, 05:15:56 am »
Definite inexpensive.

As I recall from previous threads, its hard to get under $200/channel.
 

Offline BravoV

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Re: Where can I find inexpensive differential probes?
« Reply #2 on: October 26, 2015, 05:24:18 am »
Nothing fancy, no high voltage, no high bandwidth and for educational, why not use two probes with both ground alligator clips connected together, and use both tips for differential probing.

Of course, this technique has limitation and you should aware of it.

Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #3 on: October 26, 2015, 06:32:10 am »
Nothing fancy, no high voltage, no high bandwidth and for educational, why not use two probes with both ground alligator clips connected together, and use both tips for differential probing.

Of course, this technique has limitation and you should aware of it.

Using the A-B differential probing method would limit me to two channels.
 

Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #4 on: October 26, 2015, 06:39:05 am »
Definite inexpensive.

As I recall from previous threads, its hard to get under $200/channel.

Shooting for $50 a probe. They can be 1 MHz probes for all I care, my main goal is just to get 4 differential channels. If I need to do high speed probing I can use conventional methods.
 

Offline nowlan

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Re: Where can I find inexpensive differential probes?
« Reply #5 on: October 26, 2015, 07:14:10 am »
I think pintek is as good you will find. Still not cheap enough for me.
 

Offline nidlaX

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Re: Where can I find inexpensive differential probes?
« Reply #6 on: October 26, 2015, 08:31:58 am »
Definite inexpensive.

As I recall from previous threads, its hard to get under $200/channel.

Shooting for $50 a probe. They can be 1 MHz probes for all I care, my main goal is just to get 4 differential channels. If I need to do high speed probing I can use conventional methods.
I just made a search recently and found nothing below the ~$170 range in all the usual places. If you're interested in DIY, this write up might give you some ideas: https://xellers.wordpress.com/electronics/1ghz-active-differential-probe/

EDIT: On second thought, I'm not sure if this is what you're looking for. There have been a few projects on this forum researching DIY, low cost differential probes with modest bandwidth. Not sure if any of them have iterated to completion though.
« Last Edit: October 26, 2015, 08:43:23 am by nidlaX »
 

Offline Pinkus

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I will sell one!
« Reply #7 on: October 26, 2015, 09:28:49 am »
I purchased a 20 Mhz, 450 Vpp 100:1 / 10:1 differential probe on ebay a year ago.
I barely used it as I needed higher voltage and purchased a (expensive) Pintek DP100 (6500V, 100 Mhz) differential probe later, which I am now using - so I can and will sell the other differential probe.

The seller buildt it by himself, the schematic and PCB is based on an article in an Elektor magazine. It comes calibrated and in a housing including a buildt-in power supply and is nicely shielded internally. The full (english) article from Elektor including schematics is available. I will sell for the price I purchased it for which is pretty attractive:  Price will be 75 Euros including shipping in Europe for payments via bank transfer. Paypal is possible but will add 3% paypal fee.

Non Europe countries: I can ship to other parts of the world too, probably ~ 10 Euro more for the shipping costs (I have to check first). But you should know that the buildt-in power supply is for 220-240V AV. For 110V you either need to change the internal transformer (2x 15V 3VA) or you will need to connect the supply voltage from an external source.

If interested, please send a PM, I can provide addl. information (pictures, scope pictures etc.) then.
 

Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #8 on: October 26, 2015, 07:22:28 pm »
That's a shame that there are no cheap probes. What probes are compatible with extra pins on the Rigol DS4000 series scope?
 

Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #9 on: October 26, 2015, 07:36:55 pm »
I don't understand why these things are so expensive, isn't it just a few opamps inside them?
 

Offline fpliuzzi

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Re: Where can I find inexpensive differential probes?
« Reply #10 on: October 26, 2015, 07:40:46 pm »
I'll have to leave the question about what probes are compatible with the extra pins on the Rigol DS4000 series scope to others. I haven't personally used the following differential probe, but some forum members may find that it would suit their present needs if their requirements are somewhat modest.

I came across the $79.00 'QuantAsylum' differential probe about a year ago. If I didn't already own a LeCroy AP031 differential probe at that point I probably could have lived with its CAT I 150Vrms (800V momentary surge) and 4MHz bandwidth limitations since I mostly work on audio circuits.

The following page has lots of technical data about the probe's performance.

www.quantasylum.com/content/Products/QA190.aspx

Also, the "low distortion, low noise" differential probe (their words) has an AC current clamp feature built-in (15A max), plus a 15 day money back quarantee.

NOTE: Their spec sheet states that the max input voltage is 150Vrms or +/-150V DC.
Derate by 70% per decade over 50KHz (eg 500KHz max voltage is 0.3 x 150 = 45Vrms).
 

Offline pakesson

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Re: Where can I find inexpensive differential probes?
« Reply #11 on: October 26, 2015, 08:12:51 pm »
Here's one you can build yourself fairly cheaply, https://github.com/newaetech/chipwhisperer/tree/master/hardware/tools/diffprobe. I'm not sure about the actual performance, but it's based on the AD8129 (http://www.analog.com/media/en/technical-documentation/data-sheets/AD8129_8130.pdf) which is a 270 MHz differential amplifier. Maybe good enough for (low voltage) hobby stuff?

You can also buy it as a blank pcb (http://store.newae.com/differential-probe-blank-pcb/) or assembled and tested (http://store.newae.com/differential-probe-assembled-tested/) if you want to save some time.

It's designed by Colin O'Flynn (the ChipWhisperer guy), and some more documentation can be found on the ChipWhisperer wiki at http://newae.com/sidechannel/cwdocs/naecw501_hwdiffprobe.html.

(I have one on the pre-assembled ones, but I haven't tested it yet)
 

Offline commongrounder

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Re: Where can I find inexpensive differential probes?
« Reply #12 on: October 26, 2015, 09:41:36 pm »
That's a shame that there are no cheap probes. What probes are compatible with extra pins on the Rigol DS4000 series scope?

Rigol makes a series of compatible active current and voltage probes for the DS4000/6000 scopes.  There is one adaptor that allows certain Tektronix active probes to be used on the scopes.  All of these are listed on the RigolNA web site under "Accessories".  And all are pricey! :)
 

Online tautech

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Re: Where can I find inexpensive differential probes?
« Reply #13 on: October 26, 2015, 09:54:01 pm »
I don't understand why these things are so expensive, isn't it just a few opamps inside them?
Full isolation would be the best solution but alas few scopes come with it.

Consider this:
http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=404&id=27&tid=1&T=2

Recent thread:
https://www.eevblog.com/forum/testgear/siglent-isfe-scope-front-end-isolator-any-opinions/
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Offline nctnico

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Re: Where can I find inexpensive differential probes?
« Reply #14 on: October 26, 2015, 10:35:04 pm »
Siglent's ISFE looks like a good buy if you are not after high frequencies. Add a simple 1:1 probe and you are all set (like the dirt cheap Hantek PP80 which has isolated BNCs).
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline Mechatrommer

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Re: Where can I find inexpensive differential probes?
« Reply #15 on: October 26, 2015, 11:44:20 pm »
I don't understand why these things are so expensive, isn't it just a few opamps inside them?
Full isolation...
why add injury to the insult?


I don't understand why these things are so expensive, isn't it just a few opamps inside them?
and hours of labours work... if you can mitigate it to yourself then yes, its just a few opamps, passives, a pcb and an enclosure+probes cabling...
Nature: Evolution and the Illusion of Randomness (Stephen L. Talbott): Its now indisputable that... organisms “expertise” contextualizes its genome, and its nonsense to say that these powers are under the control of the genome being contextualized - Barbara McClintock
 

Online tautech

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Re: Where can I find inexpensive differential probes?
« Reply #16 on: October 27, 2015, 02:59:52 am »
I don't understand why these things are so expensive, isn't it just a few opamps inside them?
Full isolation...
why add injury to the insult?
;D  ;)
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Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #17 on: October 27, 2015, 04:06:17 am »
Here's one you can build yourself fairly cheaply, https://github.com/newaetech/chipwhisperer/tree/master/hardware/tools/diffprobe. I'm not sure about the actual performance, but it's based on the AD8129 (http://www.analog.com/media/en/technical-documentation/data-sheets/AD8129_8130.pdf) which is a 270 MHz differential amplifier. Maybe good enough for (low voltage) hobby stuff?

You can also buy it as a blank pcb (http://store.newae.com/differential-probe-blank-pcb/) or assembled and tested (http://store.newae.com/differential-probe-assembled-tested/) if you want to save some time.

It's designed by Colin O'Flynn (the ChipWhisperer guy), and some more documentation can be found on the ChipWhisperer wiki at http://newae.com/sidechannel/cwdocs/naecw501_hwdiffprobe.html.

(I have one on the pre-assembled ones, but I haven't tested it yet)

Not exactly a flat response. There is a cliff between DC and 2 MHz, then in the middle there is a over 6dB of gain. I don't think I could make reliable measurements with this device, I was hopping for a maximally flat response from DC to x MHz.

« Last Edit: October 27, 2015, 05:37:04 am by nbritton »
 

Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #18 on: October 27, 2015, 04:41:51 am »
Would a balun work? Doesn't that take a differential pair and convert it via a transformer to a single ended connection?

http://www.amazon.com/Channel-Video-BNC-RJ45-Balun/dp/B0056KLG52

The problem with regular probes is their ground is all bonded to the same point, so if you hooked them up to different points in the circuit you would short out the circuit. If you had a balun transformer wouldn't that technically isolate the channels? Although wouldn't that short out the component your testing unless you put the balun in series. hmm. Why does this stuff have to be so expensive, maybe I should find a cheaper hobby.
« Last Edit: October 27, 2015, 04:52:15 am by nbritton »
 

Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #19 on: October 27, 2015, 05:05:55 am »
That's a shame that there are no cheap probes. What probes are compatible with extra pins on the Rigol DS4000 series scope?

Rigol makes a series of compatible active current and voltage probes for the DS4000/6000 scopes.  There is one adaptor that allows certain Tektronix active probes to be used on the scopes.  All of these are listed on the RigolNA web site under "Accessories".  And all are pricey! :)

Rigol wants $2k for their RP7080 probe! That's almost as much as I paid for the scope, and here I thought the scope would be my biggest purchase cost, nope, it's the damn probes.
« Last Edit: October 27, 2015, 05:08:34 am by nbritton »
 

Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #20 on: October 27, 2015, 05:22:32 am »
I don't understand why these things are so expensive, isn't it just a few opamps inside them?
Full isolation would be the best solution but alas few scopes come with it.

Consider this:
http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=404&id=27&tid=1&T=2

Recent thread:
https://www.eevblog.com/forum/testgear/siglent-isfe-scope-front-end-isolator-any-opinions/

That looks cool except for the fact that it has Siglents name on it. Are there any other isolators that are not made by Siglent?
 

Online tautech

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Re: Where can I find inexpensive differential probes?
« Reply #21 on: October 27, 2015, 06:53:53 am »
That's a shame that there are no cheap probes. What probes are compatible with extra pins on the Rigol DS4000 series scope?

Rigol makes a series of compatible active current and voltage probes for the DS4000/6000 scopes.  There is one adaptor that allows certain Tektronix active probes to be used on the scopes.  All of these are listed on the RigolNA web site under "Accessories".  And all are pricey! :)

Rigol wants $2k for their RP7080 probe! That's almost as much as I paid for the scope, and here I thought the scope would be my biggest purchase cost, nope, it's the damn probes.
:-DD
Yep.
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Online tautech

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Re: Where can I find inexpensive differential probes?
« Reply #22 on: October 27, 2015, 07:01:21 am »
I don't understand why these things are so expensive, isn't it just a few opamps inside them?
Full isolation would be the best solution but alas few scopes come with it.

Consider this:
http://www.siglentamerica.com/prodcut-fjxx.aspx?fjid=404&id=27&tid=1&T=2

Recent thread:
https://www.eevblog.com/forum/testgear/siglent-isfe-scope-front-end-isolator-any-opinions/
Are there any other isolators that are not made by Siglent?
Not that I'm aware of, they are a simple elegant well priced solution.
As I've mentioned in the ISFE tread you'll need to check your scopes input BNC spacings for a then very simple installation.
Also ensure you have 200:1 attenuation for the input settings.
Quote
That looks cool except for the fact that it has Siglents name on it.

Can you swallow your pride?
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Siglent Youtube channel: https://www.youtube.com/@SiglentVideo/videos
 

Offline nbrittonTopic starter

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Re: Where can I find inexpensive differential probes?
« Reply #23 on: October 27, 2015, 07:15:47 am »
I'll have to leave the question about what probes are compatible with the extra pins on the Rigol DS4000 series scope to others. I haven't personally used the following differential probe, but some forum members may find that it would suit their present needs if their requirements are somewhat modest.

I came across the $79.00 'QuantAsylum' differential probe about a year ago. If I didn't already own a LeCroy AP031 differential probe at that point I probably could have lived with its CAT I 150Vrms (800V momentary surge) and 4MHz bandwidth limitations since I mostly work on audio circuits.

The following page has lots of technical data about the probe's performance.

www.quantasylum.com/content/Products/QA190.aspx

Also, the "low distortion, low noise" differential probe (their words) has an AC current clamp feature built-in (15A max), plus a 15 day money back quarantee.

NOTE: Their spec sheet states that the max input voltage is 150Vrms or +/-150V DC.
Derate by 70% per decade over 50KHz (eg 500KHz max voltage is 0.3 x 150 = 45Vrms).

I'm not sure this will work, I'm confused, at the bottom of their spec sheet it says their probe isn't isolated. Isn't isolated inputs implied on a differential probe? The whole reason I'm looking at differential probes is because I need isolated channels. right? Or are they talking about a different kind of isolation?

 

Offline forrestc

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Re: Where can I find inexpensive differential probes?
« Reply #24 on: October 27, 2015, 07:23:00 am »
Where can I find inexpensive differential probes? I have a four channel scope and I'd like to probe across four individual components in circuit so that I can study their properties for educational purposes. I don't need anything fancy or high voltage or high bandwidth.

FYI, The problem seems to be that 'differential' often seems to be equated to 'isolated'.   Differential = fairly cheap (aka low vos opamp and some passives), isolated = expensive (think about moving a high accuracy signal across a isolation barrier).

It sounds like you want differential instead of isolated.  In the past I've just used a relatively low offset rail to rail quad opamp configured as a instrumentation amplifier.  $1 on a breadboard.

I like the looks of the AD8129/AD8130 used by the chip whisperer differential probe linked to by someone else.  I might get a couple for future use.

 


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