Suggestions for DC current probes

[rx8pilot]

I am hoping to find some suggestions for DC current probes. They are expensive, so hearing some real world feedback may help me avoid an expensive mistake or spending too much.

General specs:
>30Mhz
One low current (5-10A) with low noise.
One medium current 30A continuous.

DIY (if that is even possible) is totally out. I need a proven and reliable probe. Reasonably modern is preferred. I have a Keysight InfiniVision scope so if it interfaces direct that would be great (Agilent/Keysight models). External power supply is totally fine too if it is more affordable or better in technical capability.

The goal is to find a professional tool at a good price, not the cheapest/crappiest/knock-off thing. Hoping someone out there knows of some model that always seems to show up on eBay that would be a good fit.

Thanks in advance......

[Someone]

There are only two manufacturers for these range of high frequency probes, Tek and Hioki. I've never seen the Hioki branded probes for sale but they may be available inside Japan. You will see them available as:
Agilent/Keysight: N2782,N2783 (proprietary but well known interface that happens to match your scope)
Lecroy: CP030,CP031 (proprietary interface, no known adaptions?)

Cheaper and easier might be the indigenous Tek probes:
Tektronix: TCP312,TCP305
They run from a bulky power supply which has a convenient BNC output and are more common than the above probes that meet your edge case requirements.

Current probes for 15A RMS are much more common, and as with all current measurements you can play tricks with impedance and windings to change their response. We make use of "dumb" DC clamps for those higher DC currents you are looking at.

[D3f1ant]

You could consider the Keysight->TEK adapter (N2744A) to open the possibility of using some 2nd hand TEK current probes which are apparently good. I think the Keysight even recognizes them autoprobe style.

Your options are really limited if you don't want a dodgy/semi accurate tool. I decided current probes are too expensive to be tied to a brand of scope so have gone with Hioki on the assumption the probe will be around a lot longer than the scope. TEquipemnt sells Hioki probes so can use the eevblog discount.

The 30A probes require an exernal PSU...so be prepared 

[ez24]

What about a Tek P6021 ?  I know it is old but it is NOS (still in sealed bag).   I am not sure what it is so I do not know if it fits your needs.  It is just the current probe and termination (in bag) with manual.  Guaranteed

[rx8pilot]

Thank you.  I took a look at the Tek options. They seem like they are more than capable - high frequency and high current. They are a similar price as the Keysight probes. Do you suppose the external amplifier may offer an improvement in low mA measurments?

Hioki makes the Keysight/Agilent current probes?


Sent from my horrible mobile....

[D3f1ant]

Yes Hioki make them for everybody apart from Tek. If you want sensitivity, Hioki make new sensitive 1V/1A models that have not found their way down the rebrand ladder yet.
https://www.hioki.com/en/products/detail/?product_key=5846

[ez24]

rx8pilot PM sent

[tautech]

What about a Tek P6021 ?  I know it is old but it is NOS (still in sealed bag).   I am not sure what it is so I do not know if it fits your needs.  It is just the current probe and termination (in bag) with manual.  Guaranteed

They're AC only and no good at all for DC.

Very good AC current probe even though originally released decades ago still available new but the price is truly shocking ~$3k

[rx8pilot]

The crazy thing is that they seem to hold value. These suckers will melt down a credit card in a hurry. I was hoping there was a little known model that has a lower price, but that does not seem to be the case at all. $2k seems to be the starting line for used.

Sent from my horrible mobile....

[nctnico]

For low voltage I'd go for a current shunt resistor and a differential pre-amplifier so you can make floating measurements. In many circuits using SMD components you'll have to break the loop anyway so connecting a current shunt isn't much different. The reason current probes use hall+transformer is because they are traditionally constructed to clamp over a wire so you don't have to alter the circuit but with SMD that is no longer an option. Also a current shunt is much more precise: 0.1% versus 1.5% or worse for the current probe.

[tautech]

Carlos, Siglent have CP5030, a DC to 50 MHz 30A current probe. It has 2 sensitivity ranges with 1 or 10 mA resolution.
http://siglentamerica.com/prodcut-fjxx.aspx?fjid=4797&id=-1&tid=1&T=1

There's a link to the manual on the page linked above that lists detailed specs for all the models.

List for the one I've mentioned is ~$2600.

[chris_leyson]

LEM make closed loop Hall effect current transducers, bandwidth is only a few hundred kHz, but they use a Hall effect sensor and a feedback winding to null out the DC field. LEM LTSP 25-NP is a PCB mount example. Probably not very practical from a general purpose current probe point of view but they are reasonably accurate.

[joeqsmith]

What sort of current do you need at 30MHz?   Check the derating curves. 

For home hobby work, I can't justify spending a lot on one.  For DC I too use a few different LEMs, my modified UT210E or a shunt.  LEMs 
For higher frequencies I have my old modified Tektronix P6042 (DC-100MHzish).  For higher currents I use a Pearson.  I would guess I have under $100 invested.  The Tektronix was non-working when I received it for free.  The Pearson came from one of my trips to the Dayton HAM show.   The  LEMs I have were all pulls.  Antique shunts were given to me by an old friend of mine.   The UT210E was the high dollar ticket!   

[rx8pilot]

For low voltage I'd go for a current shunt resistor and a differential pre-amplifier so you can make floating measurements. In many circuits using SMD components you'll have to break the loop anyway so connecting a current shunt isn't much different. The reason current probes use hall+transformer is because they are traditionally constructed to clamp over a wire so you don't have to alter the circuit but with SMD that is no longer an option. Also a current shunt is much more precise: 0.1% versus 1.5% or worse for the current probe.

Definitely - I recently purchased two LeCroy 1855A amplifiers for current sense resistor and other uses. Previously, I had a lower performance Tek amplifier and it was my main current measuring tool. The probes would be for parts of the circuit that already have a wire available or a specific test on a section of a circuit.

These are for SMPS design, power monitoring, etc. The slew rate (di/dt) is generally what I am after more than the RMS current which will max out at about 15A. That is what the high bandwidth is helpful for. My next design is using eGan FET's that have very fast edge rates.

Carlos, Siglent have CP5030, a DC to 50 MHz 30A current probe. It has 2 sensitivity ranges with 1 or 10 mA resolution.
http://siglentamerica.com/prodcut-fjxx.aspx?fjid=4797&id=-1&tid=1&T=1

There's a link to the manual on the page linked above that lists detailed specs for all the models.

List for the one I've mentioned is ~$2600.

Are those models Hioki as well? Do they need any amplifier or special power supply?

[HighVoltage]

I have 3 Agilent / Keysight DC current probes

1147B, 15A / 50 MHz
1147A, 15A / 50 MHz
N2893A, 15A / 100 MHz

They all interface directly to the Agilent scope connector and they are recognized by the Infiniivision scopes.
Once in a while you can get lucky with these on the secondary market

I bought two of them broken and repaired them:

https://www.eevblog.com/forum/repair/agilent-1147b-current-probe-%282013%29-repair-need-advise/

And

https://www.eevblog.com/forum/testgear/agilentkeysight-n2893a-current-probe-%28teardown-and-repair%29/

If you have the time to wait, you can get them under $ 1000

[rx8pilot]

Thanks for those links. I am in no major hurry, so maybe I could wait for a deal or a damaged cable option. Anything under $1000 would be worth some elbow grease.

It would be nice to be have the direct interface for sure.

[georges80]

Somthing like -> http://www.ebay.com/itm/Tektronix-TM502A-Power-module-AM-503B-Current-Probe-Amplifier-/112081913785?hash=item1a189a47b9:g:lNEAAOSwtnpXom9R

Don't get the AM503, you want the AM503B.

and a Tek A6302 probe is what I use.

I picked my 'set' up for about $600 for all 3 units (power supply, current probe amp and the current probe).

They work very well and have used them for several years now.

The combination can reliably measure current in the 10mA range and of course is AC/DC measurement capable.

cheers,
george.

[HighVoltage]

If you want a good general purpose DC current probe, look at the:

Tektronix A622, it is 100A but only 100 kHz
It is made by AEMC, Model SL261
and also sold as Fluke, 80I-110S
or Agilent 1146A

These are really great general purpose current probes, just may be too slow for your applications.

[rx8pilot]

Somthing like -> http://www.ebay.com/itm/Tektronix-TM502A-Power-module-AM-503B-Current-Probe-Amplifier-/112081913785?hash=item1a189a47b9:g:lNEAAOSwtnpXom9R

Don't get the AM503, you want the AM503B.

and a Tek A6302 probe is what I use.

I picked my 'set' up for about $600 for all 3 units (power supply, current probe amp and the current probe).

They work very well and have used them for several years now.

The combination can reliably measure current in the 10mA range and of course is AC/DC measurement capable.

cheers,
george.

Is the power supply the TM501 module on the right side of the amplifier? $600 would be amazing! Especially if I could find 2 of them for a similar price. Added those model numbers to the list.

Do you suppose there are any significant performance considerations compared with the more modern probes? Other than the size being a lot smaller - are there any measurement limitations with these that may not exist in the Keysight (Hioki) models?

[georges80]

Yeah, the TM5xx is the power supply unit. There's ones with 2 slots and ones with 1 slot. You only need the 1 slot (smaller), but often the 2 slots are all you can find.

I see no advantage with a newer unit (if you have room for the AM503B amplifier). I like that the amplifier lets you get down to low current levels right from the probe output.

Anyhow, like I wrote, I've had my setup for several years (probably near 10) and never had any problems with the unit. I've tested it against known DC current levels and it's 'close enough' to dead on. I use it to test/design LED drivers up to 10A output and the Tek setup works just fine. The 'output' of the AM503B goes straight to any 50 ohm input (no need to worry about tek/agilent 'fancy powered scope bnc's).

I've used it it my older tek scope and now with my agilent scope. Any scope from the last 15+ years allows you to configure a channel for Amp display and set the scaling factor, with that you get direct current display in the appropriate scaled values so no mental arithmetic needed to convert the readings on the scope.

cheers,
george.

[tautech]

Carlos, Siglent have CP5030, a DC to 50 MHz 30A current probe. It has 2 sensitivity ranges with 1 or 10 mA resolution.
http://siglentamerica.com/prodcut-fjxx.aspx?fjid=4797&id=-1&tid=1&T=1

There's a link to the manual on the page linked above that lists detailed specs for all the models.

List for the one I've mentioned is ~$2600.

Are those models Hioki as well? Do they need any amplifier or special power supply?

They come with a wallwart, termination and BNC cable as illustrated in the manual I mentioned you can download.
I couldn't say for sure who Siglent sources them from but I'd doubt it's Hioki, there's other Asian current probe manufacturers  that I'm aware of. 

[rx8pilot]

Yeah, the TM5xx is the power supply unit. There's ones with 2 slots and ones with 1 slot. You only need the 1 slot (smaller), but often the 2 slots are all you can find.

I see no advantage with a newer unit (if you have room for the AM503B amplifier). I like that the amplifier lets you get down to low current levels right from the probe output.

Anyhow, like I wrote, I've had my setup for several years (probably near 10) and never had any problems with the unit. I've tested it against known DC current levels and it's 'close enough' to dead on. I use it to test/design LED drivers up to 10A output and the Tek setup works just fine. The 'output' of the AM503B goes straight to any 50 ohm input (no need to worry about tek/agilent 'fancy powered scope bnc's).

I've used it it my older tek scope and now with my agilent scope. Any scope from the last 15+ years allows you to configure a channel for Amp display and set the scaling factor, with that you get direct current display in the appropriate scaled values so no mental arithmetic needed to convert the readings on the scope.

cheers,
george.

These models seem like a great bang for the buck overall. I have enough room for a pair of them on my bench so the size will not slow me down. Unless I get lucky and find an unusual deal on an Agilent model - I believe these are the best fit as they appear to have the performance and a modest price tag. Thank you for sharing your thoughts and experience.

[timb]

Yeah, the TM5xx is the power supply unit. There's ones with 2 slots and ones with 1 slot. You only need the 1 slot (smaller), but often the 2 slots are all you can find.

I see no advantage with a newer unit (if you have room for the AM503B amplifier). I like that the amplifier lets you get down to low current levels right from the probe output.

Anyhow, like I wrote, I've had my setup for several years (probably near 10) and never had any problems with the unit. I've tested it against known DC current levels and it's 'close enough' to dead on. I use it to test/design LED drivers up to 10A output and the Tek setup works just fine. The 'output' of the AM503B goes straight to any 50 ohm input (no need to worry about tek/agilent 'fancy powered scope bnc's).

I've used it it my older tek scope and now with my agilent scope. Any scope from the last 15+ years allows you to configure a channel for Amp display and set the scaling factor, with that you get direct current display in the appropriate scaled values so no mental arithmetic needed to convert the readings on the scope.

cheers,
george.

These models seem like a great bang for the buck overall. I have enough room for a pair of them on my bench so the size will not slow me down. Unless I get lucky and find an unusual deal on an Agilent model - I believe these are the best fit as they appear to have the performance and a modest price tag. Thank you for sharing your thoughts and experience.

If you need a TM501 (single slot) or TM503 (three slot) let me know, I have both, fully restored with brand new caps (major PITA to do) plus I removed the power cord and added a real IEC connector to the TM503.

[rx8pilot]

Do you have the probes or just the amplifier? Does it provide power or is that a separate thing?

[rx8pilot]

I think I figured it out -

The TM501 and 503 are the powered chassis for the AM5xx amplifiers? Is that right?

[georges80]

^ yes.

cheers,
george.

[David Hess]

Yeah, the TM5xx is the power supply unit. There's ones with 2 slots and ones with 1 slot. You only need the 1 slot (smaller), but often the 2 slots are all you can find.

Is a drawer installed into the right side of the TM502A for holding the probe?

[timb]

I think I figured it out -

The TM501 and 503 are the powered chassis for the AM5xx amplifiers? Is that right?

Exactly, but they're not just for the AM5xx amplifiers! The TM 5xx are Tek's universal power mainframes used from the mid-70's until the late 80's. They produced a few dozen separate instruments for them. Everything from DMMs and power supplies to frequency counters, function generators, amplifiers and even tiny oscilloscopes!

The last digit in the model number of the TM (which I assume stands for Tek Mainframe) series designates how many slots it contains. So a TM 501 is a single slot unit and a TM 506 is a six slot unit.

The various plugin designations have similar names:

AM5xx = AMplifier
PG5xx = Pulse Generator (Square Waves)
SG5xx = Sine Generator
FG5xx = Function Generator
TG5xx = Time Mark Generator
DM5xx = Digital Multimeter
PS5xx = Power Supply

Plus several other types.

They're surprisingly useful mainframes as you can often get the plugins pretty cheap. I just picked up a SG 504 250MHz to 1GHz Leveled Sinewave generator for $100!

Just make sure you don't accidentally buy a TM 5000 series mainframe or plugin, as they're not backwards compatible with the 500 series.

The 500 series mainframes are pretty simple. It's essentially a huge transformer with a few dedicated windings (providing low voltage AC) and (rectified and filtered) 12VDC for each slot on the mainframe along with a high current (rectified and filtered) 32VDC bus shared among all the slots. There's also one NPN and PNP transistor for each slot (bolted to the metal frame for heatsinking).

If you buy a mainframe from eBay, I'd recommend replacing the caps. There's a couple of 5000uF ones plus a big 20,000uF one (if I remember correctly and at least for the three slot unit). Don't try desoldering the wires that go from the board to the transformed; instead just unbolt the transformer and unscrew the board and remove them together. Once out of the mainframe there's plenty of room to easily unsolder the caps. They use those old 4 terminal Sprague caps, however the hole spacing was standard, so you can replace them with your choice of snap-in style caps.

[georges80]

I've put up the PDF manuals for the A6302 and the AM503B on dropbox ->

https://www.dropbox.com/sh/px9ko9dh10375r3/AADyieBVn4oMcGY3PwvlrDeGa?dl=0

cheers,
george.

[rx8pilot]

Thank you George!

The notes on these Tek probes is very helpful - I was not looking at them before. It looks like they are the best value out there while meeting the technical needs. Fantastic.

[woodchips]

Silly question, why do you need DC measurements?

A low frequency DC&AC probes are cheap, as are AC only probes, when I was looking around that is what I decided on, but so far yet to use the DC&AC probe and wondering what I am missing.

[joeqsmith]

Silly question, why do you need DC measurements?

A low frequency DC&AC probes are cheap, as are AC only probes, when I was looking around that is what I decided on, but so far yet to use the DC&AC probe and wondering what I am missing.

Looking at biased AC signals.   Output from a rectifier, etc.

[Someone]

Silly question, why do you need DC measurements?

A low frequency DC&AC probes are cheap, as are AC only probes, when I was looking around that is what I decided on, but so far yet to use the DC&AC probe and wondering what I am missing.

Looking at biased AC signals.   Output from a rectifier, etc.

Yes, you can hook up two probes to the same signal to look at the DC-xxxkHz and xxxHz-xxxMHz separately. Its unusual to need the DC and MHz signal accurately combined simultaneously and I've worked on many power supplies with an AC scope probe and a DC clamp meter.

[georges80]

DC and AC simultaneous measurements allows you to monitor things like LED current regulated switchers that transition from DC to various PWM outputs at various times. Many of my LED drivers will go from DC output to PWM output and transition between at various output levels (e.g. strobe modes).

Being able to monitor the entire current profile on a single screen and capture it for documentation and also for average current measurements is something that a single AC/DC capable current probing setup allows you to do very easily. i.e. we're talking about a dynamic situation that goes from DC to DC/PWM to DC.

Anyhow, given the demographics of this Forum are you actually hinting that a certain piece of test equipment isn't 'needed' 

cheers,
george.

[rx8pilot]

Silly question, why do you need DC measurements?

A low frequency DC&AC probes are cheap, as are AC only probes, when I was looking around that is what I decided on, but so far yet to use the DC&AC probe and wondering what I am missing.

In my case - I almost never work on AC power at all. My products are DC from beginning to end.
I have to document inrush current and design the eFuse circuits to match. This process requires the edge rate of the current waveform to be known. Switching losses, transient response,  RDS(on), efficiency, are other applications. The shape of the curve provides insight into various problems in PCB layout or components. When trying to build DC power electronics - especially high performance - DC currents move fast. I am always trying to improve switching speeds by lowering parasitic inductance and faster switching devices. The edge rates are getting really fast.

I am also buying high-performance differential amplifiers to measure current sense resistors in places that are impossible to get these relatively big probes.

[nctnico]

I'm not sure where your product goes but fast edge rates seem unwanted to me for EMI/EMC problems. A fast edge can couple into circuit easely causing all kinds of mayhem.

[rx8pilot]

That is the challenge. The slow edges are less efficient and the fast edges make a ton of noise. The eGAN FETS are on the table now and offer the possibility of super fast switching with nearly no dead time. The transistor transits the linear region very fast and takes advantage of the low Rds(ON) even with fast switching frequencies. The next challenge is to deal with the resulting EMI mess it can make  - as you pointed out. It is a new area for me, but I think it is a good pursuit. Smaller and more efficient power conversion and management.

A less challenging fast edge rate problem I have to deal with is step currents and inrush created by the loads. I have to be able to know what the loads need and how to make the supply, protection, and monitoring systems stable in the face of fast changing currents. In those cases, I am doing what I can to slow down the slew rates to something more manageable.

[Someone]

DC and AC simultaneous measurements allows you to monitor things like LED current regulated switchers that transition from DC to various PWM outputs at various times. Many of my LED drivers will go from DC output to PWM output and transition between at various output levels (e.g. strobe modes).

Being able to monitor the entire current profile on a single screen and capture it for documentation and also for average current measurements is something that a single AC/DC capable current probing setup allows you to do very easily. i.e. we're talking about a dynamic situation that goes from DC to DC/PWM to DC.

Except here the OP is asking for corner case specifications while wanting it cheap, so alternatives are being suggested. You can measure edge rates of switching supplies with an AC probe, the content below 1kHz is not needed. At the same time you can determine or measure the DC separately. Its convenient to do it all at once but look at the OPs requirements they originally stated, there are precious few probes with both the bandwidth and a 30A DC continuous rating.

[David Hess]

Yes, you can hook up two probes to the same signal to look at the DC-xxxkHz and xxxHz-xxxMHz separately. Its unusual to need the DC and MHz signal accurately combined simultaneously and I've worked on many power supplies with an AC scope probe and a DC clamp meter.

This will almost always *not* work.  Wide bandwidth AC only probes saturate at low DC currents making them useless if there is DC bias.  You can use them to measure in series with a capacitor but not a switch or diode.  A Tektronix P6021 saturates at 0.5 amps and a P6022 saturates at 0.2 amps.

Wide bandwidth AC/DC probes have a counter winding which suppresses DC saturation. The counter winding is also how they are able to measure DC current.

[rx8pilot]

Except here the OP is asking for corner case specifications while wanting it cheap, so alternatives are being suggested.

To be clear, I am not looking for cheap at the expense of function. I am looking for the function at the lowest practical price. In all reality, the 30Mhz is likely a solid 5x more than a will see any time soon - but I prefer the headroom in bandwidth. The max RMS DC I would expect on a normal day is 15A, so I wanted to double that and still have some transient headroom for the day when I want to push the DUT to it's destruction. Some days I would measure steady state DC current, others will be looking at how fast can the circuit switch before it becomes an unwanted radio station.

The biggest lesson so far is that there are indeed precious few probes in this range to pick from. Thankful to learn of the Tek DC options, as they seem to fit the bill and are not very expensive. Really thankful for the discussion - thank you all.

[Someone]

Yes, you can hook up two probes to the same signal to look at the DC-xxxkHz and xxxHz-xxxMHz separately. Its unusual to need the DC and MHz signal accurately combined simultaneously and I've worked on many power supplies with an AC scope probe and a DC clamp meter.

This will almost always *not* work.  Wide bandwidth AC only probes saturate at low DC currents making them useless if there is DC bias.  You can use them to measure in series with a capacitor but not a switch or diode.  A Tektronix P6021 saturates at 0.5 amps and a P6022 saturates at 0.2 amps.

Wide bandwidth AC/DC probes have a counter winding which suppresses DC saturation. The counter winding is also how they are able to measure DC current.

There are more probes outside of the world of Tek/Hioki, AC coupled loop probes based on Rogowski coils are very versatile and are "immune" to DC bias:
http://www.pemuk.com/products/cwt-current-probe/cwt-ultra-mini.aspx

[rx8pilot]

http://www.pemuk.com/products/cwt-current-probe/cwt-ultra-mini.aspx

Pretty interesting product.


For the Tek AM503B amplifiers, I have started making efforts to buy a pair of them. One thing I noticed on at least two options is that the OVERLOAD light is lit with nothing connected. Is that an indication of a problem or does it go away when a proper probe is connected?

[David Hess]

There are more probes outside of the world of Tek/Hioki, AC coupled loop probes based on Rogowski coils are very versatile and are "immune" to DC bias:
http://www.pemuk.com/products/cwt-current-probe/cwt-ultra-mini.aspx

Those are neat but give up a lot of sensitivity and low frequency performance.  For an equivalent low frequency cutoff, they have a noise level of 750 milliamps peak-to-peak versus 750 microamps peak-to-peak or about a thousand times worse than a P6021.

It looks like the most sensitive one is good for 30 amp measurements with a useful resolution down to 100 milliamps and 20 millamps with averaging which is fine for most applications.

They are pretty expensive compared to a wide bandwidth AC or AC+DC current probe which can be found used.

[georges80]

http://www.pemuk.com/products/cwt-current-probe/cwt-ultra-mini.aspx

Pretty interesting product.


For the Tek AM503B amplifiers, I have started making efforts to buy a pair of them. One thing I noticed on at least two options is that the OVERLOAD light is lit with nothing connected. Is that an indication of a problem or does it go away when a proper probe is connected?

My AM503B WITHOUT a probe connected, flashes several LEDs on power up but NEITHER the Overload or Probe Open or Degauss lights are lit after power on.

So, no idea why they would be on in the units you are looking at to purchase...

cheers,
george.

[rx8pilot]

Well - I just purchased 2x of the AM503B's in a TM502A enclosure along with 1x of the A6302 probes. Still looking for a second probe but I am thankful to have these units on the way. As always, eBay is a cross-your-fingers endeavor. All of it is able to be returned if there is a problem.

[TheSteve]

Looks like some successful best offers - hope it all works exactly as it should.

[timb]

Well - I just purchased 2x of the AM503B's in a TM502A enclosure along with 1x of the A6302 probes. Still looking for a second probe but I am thankful to have these units on the way. As always, eBay is a cross-your-fingers endeavor. All of it is able to be returned if there is a problem.

AM503 is one of my saved searches, so earlier while browsing eBay I came across (what I think) was that very set. I got up to let the dog out, came back and the item was sold; I thought "Must have been rx8!"

I was going to PM you a link to it, but I guess you were a step ahead of me. Looked to be in nice shape, too.

[rx8pilot]

$475 for the amplifiers and another $175 for the probe. Not bad at all!

Sent from my horrible mobile....

[georges80]

Good job, I'm sure you'll be happy with their performance (assuming all is up to spec).

When you turn on the AM503B it will require you to degauss the probe. Then a few minutes later it'll light up again (as it warms up and decides you need to degauss). It'll do this a couple or so times, usually after 20 minutes or so it'll be stable for hours on end without any more requests to degauss. Just an idiosyncrasy as it warms up on each power up. It's usable once degaussed, you don't have to wait 20 mins etc to actually use it or get readings.

I use it much more often than some of my other probes (active, differential, etc) that's for sure. It can be very enlightening to see some of the current spikes that various bits of gear go through on power up - lets you see things that you would never otherwise notice... might cause lack of sleep in some cases

cheers,
george.

[lukier]

Great score! Could you do a mini-teardown of AM503B when you receive it? I have the oldest crusty AM503 with A6302 and it is not that great, the amplifier seems noisy (pick up) and drifty. I've read somewhere that modern AM503 (A & B) are much better in that regard and I have AM503A service manual, I've seen the photo of the insides somewhere on the internet and I'm curious how much different AM503B is.

[Marchello]

Inside AM503B


BR
Mark

[lukier]

Inside AM503B

Thanks 

It seems really similar to what I deduced from the AM503A service manual, still quite vintage. No massive leaf spring rotary switch and dual-ganged offset pot, but still custom attenuator module (those SIPs I guess) and MAXTEK output amplifier that is press-contact clamped into the PCB (not very cost-effective die packaging I guess). Tektronix really likes custom hybirds/modules and milk the design for a couple of decades. I think the only COTS current probe amplifier is TCPA300 :/ I still don't understand why these composite amplifiers (hall based current servo + oscilloscope front end (attenuation, ac-dc, bw limit etc) into 50 ohms) are so expensive. I got A6302 for 75 GBP and I'm not really willing to many times that amount on these silly amplifiers, hence why I cheaped out on an old AM503 in TM501  The rocket science is in the probe itself (integrated hall sensor, transformer polished down to sub-um levels, dual mu-metal shielding etc), not the amplifier.

[rx8pilot]

The price of these types of things is based on what the manufacturer can get for them - not so much what is inside. The used prices are the same thing, market based. 99.999% of the world doesn't even know what this thing is or why someone would pay any amount for it. The extremely small number of people that have a need, it is a business need. My strategy is to buy things from people that don't know what it is - liquidators and such. The companies that sell T&M offer service and some sort of QC, but the prices are quadrupled or more. As long as the random liquidator accepts returns - it is worth it to save a ton of money.

[rx8pilot]

The second A6302 probe is theoretically on it way from the most flaky eBay seller I have ever dealt with. Its either a great deal at $150 or I just got scammed.

Should have 2 current probes if luck is on my side. I learned a while ago not to get too excited about eBay stuff until it clears a few tests.

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[TheSteve]

Quite the detailed description on that second one - "USED".
I've had all kinds of fun ebay experiences - stuff that was never shipped, I've been asked for more money, I've been sent the wrong item, stuff packed in a box smaller then the item itself(a power supply).
But then it is often the items where you take a little more risk where you can get lucky and come out ahead - hopefully everything works perfect!

[rx8pilot]

Overall, I am seriously ahead on my eBay purchases. If the $150 is totally lost it is only a small dent in my record.

The previous purchase was a LeCroy DA1855 differential amplifier kit that was DOA. The seller immediately refunded the return and paid for all the shipping. I wish the unit worked, but could not have asked for a better return experience. The week before I received a different DA1855 amplifier that I seriously low-balled and works great.

If this kit functions - I will have two 50Mhz 20A current probes for a total of $850. Fingers crossed. I am on a probe rampage trying to appropriately outfit my new scope.

[H.O]

In 2012 I bought a set of AM503 and A6302 (and a single slot chassi) and got another AM503 and a P6302 for free as a result of the first set not working properly.

I've re-biased one of the probes by replacing the internal resistors and it sort of "works" but I'm pretty sure it's still not how it's supposed to be, it's quite noisy, unusable at the lower ranges and it drifts quite a bit. The other one is even worse.

These things are delicate and fragile, I can make the trace move all across the screen by simply pushing and twisting very gently on the probe head. Have tried cleaning the core and "adjusting" the spring.

I'm not sure how much of the issues comes from the probe(s) and how much comes from the amplifier. I would like to get a AM503B but if the probes are shot then I'm not sure.

[rx8pilot]

I am curious about the check out on these. If they drift, or glitch, whatever - it may be a project to learn enough to troubleshoot.

Sure would be sweet if it all just works.

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[rx8pilot]

Some of the toys arrived today - but with some challenge.

The pair of Tek AM503B current probe amplifiers and one of the current probes are here. All of it looks the part, was packed well and turned on. I tested the first amplifier with the probe through a range of currents and step currents - spot on perfect. Surprisingly good. 1A to 9A in 5.5us which is as my DC load will go.

The amplifier on the right side is not working though. It is outputting about 25mV DC, will not degauss, and does not respond to any input at all. I let it warm up for a bit, ried a number of times - still nothing.

Hoping it is simple, but fear it is a project. Tomorrow I will check the easy things, contacts, rail voltages etc.

EDIT UPDATE:
An amazing lucky break! All I did was re-seat the module and it is working fine. AWESOME! Both channels are very closely matched and agree with all my other current meters from 1 to 15A.

[georges80]

Looks good an congrats on getting some real current probes running. You'll find them incredibly useful for measuring current with the high frequency response they offer. Even checking if you have a dead phase on an alternator (dead diode in the rectifier bridge) etc etc...

There are also tricks to increase sensitivity - like multiple wraps of the sense lead through the core. There's ways to remove the effect of large static DC currents by feeding current through a wire in the opposite 'direction' through the core. Some of these tricks are in the Tek manual for the a6302 that I put up on my dropbox.

Time to play and learn

cheers,
george.

[rx8pilot]

Thanks for the manual links, I already used it to figure out what error 266 is - output not terminated to 50ohm. Glad it reminds me, but flashing 266 does not communicate much. Still waiting for the 2nd probe to arrive on Monday.

I have a solid kit of power related accessories now. Thanks George for the tips on this purchase - these were a good choice for sure.

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[D3f1ant]

Older Tek probes  really is the only option if you want a value for money proposition. Good to see you got some working ones for a decent price.

Sent from my SM-N930F using Tapatalk

[H.O]

Have you tried it/them at the low ranges, like 5 or 10mA per div? That's where mine are "problematic", well, actually a bit higher than that as well unfortunately.

[timb]

EDIT UPDATE:
An amazing lucky break! All I did was re-seat the module and it is working fine. AWESOME! Both channels are very closely matched and agree with all my other current meters from 1 to 15A.

You might want to clean the gold plated edges on the back of both modules. I use foam Swab-Its with 92% Iso, followed by a swab of DeoxIT Gold. You should also check to make sure the the pins inside the edge connectors of the mainframe are making good contact (if not just bend them out a bit) and clean them as well (I use normal DeoxIT for that).

Also, make sure you power down the mainframe before removing or inserting a module. They're not hot swappable! It can create a large spark which can damage the "gold fingers". I've repaired quite a few TM500 series modules with this problem using 36awg wire:



Glad you've got a working set!

[rx8pilot]

I am thinking I should replace the internal battery while it is apart and before I forget about it. My guess is that if the NVRAM is compromised - it would be a paid to recover from that. it seems easy enough to install a new battery - just trying to figure out if the process of replacing it will mess up the memory.


EDIT:
IT does not matter - the batteries have long since been dead and leaked all over. A little clean up and fresh batteries are in order. Once I did that and cleaned all the other terminals - they both come up just fine and seem to be spot on all the way down to 1mA with a single wire passing through which surprised me. Glad they use a fairly normal battery at least.

[David Hess]

From the documentation I have, it looks like the internal battery is used to retain the calibration data and calibration can only be done over GPIB.  That is awkward but typical of Tektronix in the 1990s.

[rx8pilot]

Excellent, these don't even have GPIB. I will look closer at the accuracy - a quick look seems rather close but I don't have any standards.

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[David Hess]

Excellent, these don't even have GPIB. I will look closer at the accuracy - a quick look seems rather close but I don't have any standards.

The service manual for the AM503B and AM5030 says:

To set the internal calibration constants of the AM 503B amplifier, you must install the GPIB test fixture. Refer to the procedure that begins on page 15.

For the record, I hate designs which require auxiliary equipment to enter calibration data.  It strikes me as just another form of Digital Rights Management and a way to enforce obsolescence.

[rx8pilot]

Those schemes are designed by the business end of the company for sure. Engineers naturally seek the shortest path while management pushes for the most profitable path regardless of how long and crooked it may be.

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[nctnico]

Those schemes are designed by the business end of the company for sure. Engineers naturally seek the shortest path while management pushes for the most profitable path regardless of how long and crooked it may be.

I'm not quite sure which way Tektronix went. For some engineers the way through proprietary interface and/or GPIB interfaces with proprietary software is the easiest  if they have to develop it.

[rx8pilot]

My 2nd A6302 current probe arrived last night - but it is not a winner. The finger release part is missing and of course that was obscured by the photos in the listing. The underlying mechanism is apparently all tied together with this plastic piece so I cannot easily 'fake it'

Shopping for bargains can sometimes be very expensive, lol. Lets see what the seller has to say. It's possible he/she has more than one of these and I can swap.

In the meantime - I am considering just fabbing up a bodge repair. If I can figure out a quick and dirty repair, it may be worth keeping it and moving on.

[tautech]

Carlos, the probe form factor and finger pull look the same as my P6021,. The finger pull should be available as a spare part. But it's not, just looked at my manual. It's just called Slide and pt# 351--0191--00

[Someone]

Its also possible to fashion a replacement, or open and close the probe with a ball point pen tip by sliding the metal plate with the holes in it. This is the "locking" mechanism.

[rx8pilot]

Its also possible to fashion a replacement, or open and close the probe with a ball point pen tip by sliding the metal plate with the holes in it. This is the "locking" mechanism.

I tried that, but something is preventing it from opening more than about a third of the way. I suspect a piece of plastic fell into a spot that is blocking movement. When I took the screws out of the probe the case did not lift off. Not sure how many small parts and springs will shoot out if I get it open. maybe I will try again tonight.

[tautech]

Its also possible to fashion a replacement, or open and close the probe with a ball point pen tip by sliding the metal plate with the holes in it. This is the "locking" mechanism.

I tried that, but something is preventing it from opening more than about a third of the way. I suspect a piece of plastic fell into a spot that is blocking movement. When I took the screws out of the probe the case did not lift off. Not sure how many small parts and springs will shoot out if I get it open. maybe I will try again tonight.

There's not much to them, just watch for the small ball bearing when they come apart.

[Gandalf_Sr]

I am considering just fabbing up a bodge repair

Have you considered making a replacement using a 3D printer?  I'm looking for a good A6302 or A6312.  I have one that I won on eBay on the way; it's supposed to work but it is an old one.

[rx8pilot]

I ended up just getting a refund from the eBay seller. I don't have the time to deal with it at the moment.

Sadly, after I shipped it back, the seller said 'just keep it' since he did not want to pay for shipping. Could have been a great score if it was free - bad timing.

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