Oscilloscope current probes and dedicated power supply RIGOL?

[riccardo.pittini]

Hi all,

I am looking around for current probes for oscilloscopes. The whole thing is part of laboratory investments (we want to take care of our students ) for a power electronic laboratory.

We bought some Rigol  DS4024 and the price/performance of the units it seems very good. Maybe just a bit noisy to be picky (temperature control on the fan would have been good to implement).

So since we got the scopes... we miss some current probes...

I had a look at some "good" current probes with bandwidth in the range of 50-100 MHz like the
- RIGOL RP1004C http://www.rigolna.com/products/accessories/rp1004c/
- RIGOL RP1002C http://www.rigolna.com/products/accessories/rp1002c/

all of them they need a additional power supply!!! (RP1000P, http://www.rigolna.com/products/accessories/rp1000p/).

Do you know what is special about this power supplied for current probes?

Do you have other suggestions for current probes with a reasonable bandwidth? (>=20MHz, I know it might seem high buy in our power electronics group we are also switching MOSFETs at 50+MHz... )


Other oscilloscope companies like LeCroy (mid-high end series) they have amazing scopes and  they also have current probes that they connect directly to the from part of the scope without additional external power supply. I did not see any RIGOL current probe with decent bandwidth that does fit directly to the channel-connector on the front part of the scope.

I've been curious about this thing since I saw that you can buy differential voltage probes that fit any oscilloscope (BNC connector) and they use a small external AC-adapter (or they run on batteries).



Thanks for the suggestions!! and...
Cheers to all from Danmark!

[alm]

Not sure what you mean by 50-100 MHz, the second one is only 1 MHz. The RP1004C is not a Rigol design, it's probably made by Hioki. Last time I checked there were only three manufacturers of these: Tektronix (the original inventors of the Hall sensor + current transformer idea), Hioki and a third one (LEM?). Agilent and Lecroy also buy their DC-100 MHz current probes from one of these.

If Rigol doesn't sell a current probe with support for the DS4000 power pins, then nobody will. These interfaces are proprietary, so a Lecroy, Tektronix or Agilent probe won't get power from a Rigol scope without hacks. Probe support for less common scope applications is going to be the weak point for a new scope manufacturer like Rigol. Tektronix, Agilent and Lecroy invest a lot in designing good probes, and obviously not a lot of time in making sure they work with other brands , it's not uncommon for a probe to determine the scope brand for some applications.

[casinada]

For Low Frequencies:
http://www.fluke.com/fluke/usen/accessories/current-clamps/i1000s.htm?PID=56280
http://www.fluke.com/fluke/usen/accessories/current-clamps/90i-610s.htm?PID=55502
High Frequency
http://www.fluke.com/fluke/usen/accessories/current-clamps/i50s.htm?PID=56306

I wouldn't trust students with $2000+ probes. No way !!!!

[nctnico]

Even with Tek or Agilent scope you'll need an extra power supply to provide power to their current probes. The oscilloscope's internal power supply just isn't beefy enough.

[alm]

casanida: yep, AC only or low frequency is much cheaper. Unfortunately some application don't allow you to act like DC doesn't exist.

Even with Tek or Agilent scope you'll need an extra power supply to provide power to their current probes. The oscilloscope's internal power supply just isn't beefy enough.

Only for the higher currents. For example the Tek TCP202A (powered from the TekProbe interface) goes up to 15 A, while the TCPA300 amplifier with TCP312 probe (pretty much same probe head, but external amplifier and power supply) goes up to 30 A. This is because the probe actually sends DC current through the probe in the opposite direction as the signal until the net DC current is zero. The Hall sensor acts like a null detector. So to measure 10 A DC the probe also has to source 10 A. This prevents core saturation. AC only probes will usually have a limit on the DC current (lower than the maximum AC current) to prevent core saturation. This can sometimes be interesting since you can't actually measure this current.

Edit: they are obviously using multiple turns for the bucking current coils. Still, the same argument applies for 10 A divided by the number of turns.

[PA4TIM]

I have three Tektronix current probes. Two need an external amplifier/powersupply (the famous P6042) The other  (P6016)  one uses a separate Tek 134 amplifier and also an external powersupply. The third one, a CT1 can be used on any scope without a powersupply.
Tek is in my opinion one of the best in Current probes. But be carefull, current probes are easy to damage. The hall sensor ones can be killed just by dropping them.

I also made some AC currentprobes with the use of a current transformer but 3dB point was only 500 kHz. Next experiment will be a mix of transformer and Hall sensor. (but as always, more projects as time)

[Alexei.Polkhanov]

Both Agilent and Tektronix had and still sell current probes with external power supply. My understanding that in newer models of oscilloscopes in addition to simple BNC connector for input they provide series of contacts to provide DC power to active probes (including current, differential) thus making it impossible to use such probe with another model of oscilloscope from different vendor. I think it sucks. If I spend $2K on current probe and cannot lend it to my friend because he has Tektronix ... WTF  I know external supply is bulky, batteries are heavy but still I would prefer to have probe that is standalone.
I think PSU is a linear supply with tracking and some adjustments for offsets.

[alm]

Yes, the power supply for such probes is generally not that difficult, just some positive and negative DC voltages. The trickiest part would be the connection if you don't want to ruin the probe. How to do this for Agilent probes has been discussed on this forum.

For the higher end probes the integration allows for better performance, since the probe can for example pass calibration parameters to the scope. Not an issue for your basic 100 MHz current probe, but definitely an issue for that nice 20 GHz differential probe (which uses the same interface as some current probes).

[Simon Loell]

Does it have to be very accurate?

I'm in the beginning of making my own current probe, but for small battery applications, to monitor idle and standby currents. I build a version of Davids uCurrent to hook onto my scope.
I know it has a lot of limitations f.x. dynamic area. But this can be solved using a OP-AMP with a wider supply range.
http://nerdclub.dk/2013/09/uampere-meter-og-psu-med-stoj/

The bandwith is for my version limited to around 28MHz (OP-AMP BW), but if you search for other OP-AMPs I'm sure you can find one for your BW need.
And if your budget is over 1.000 US$ I'm pretty sure you can find several OP-AMPs within this limit.

Regarding the use of an external power supply for the current probe, then it propably has something to do with the amount of noise generated by a standard PSU, and also something about potentials. Since you want both positive and negative currents to be measures, a grounded reference PSU will not work.

Maybe Davids uCurrent is to small for your need, but that should only be a question of shunt size and gain.

If you're interested we could make this into a small project, maybe even in native language?

Best regards
Simon - Denmark - Nordjylland

[riccardo.pittini]

Thanks to all for the good input!!!

I know sometimes giving a probe of 2kUSD to a student sounds crazy but we have good students  and if you are designing a power supIply a current probe with a bandwidth of 100kHz ... it is like measuring DC...

What i like of the probe RP1002C is that it uses a simple ac-adapter as power supply, so actually very cheap.

When I saw the prices of the dedicated power supplies for more professional probes (20+MHz) i wondered why they are so expensive. Most of the time the voltage tolerance is 12V+-0.5V with a current of about 0.5A or a bit more. In theory you could design a very simple power supply, and if you want even linear, that would match the specifications.

Of course I guess finding the connector it is a real challenge .

Definely the ucurrent project it is a bit too low... we usually range easily up to 30A.

In my previous job i used Tektronix MSO 4000 series and now LeCroy, both they have current probes up to 150A that they do not require external power supply but of course u can you them only with their scopes.

I understand having a power supply for powering the current probes and differential probes but it cannot be as big as the oscilloscope!!! -_-

We have some Rogowski coils for measuring ac-current up to 20MHz, they are just great (battery+ac-adapter), just missing dc...


I think I will have a look at the Fluke current probes, definitely interesting.

[riccardo.pittini]

Sorry to bring up again this post... but I have been struggling on finding decent ac/dc current probes.

the post suggesting the Fluke i50s: it would have been a perfect probe (good bandwidth and you can use any power supply, it does not need a specific one) ==> but it is discontinued   

does anyone have some other suggestions?

Has somebody tried to change the special connector on Hioki current probes and use a regular external power supply?

[KD0CAC John]

Dave did a video on a current probe , it was a one of a kind I thought , and it did not use a loop of wire for measuring , it had a tip and would measure off traces .
The biggest thing relative to this thread is that it didn't cost $2,000+++ and dedicated to 1 scope .
If my memory is correct is was made in England and cost about $850 , high for my tastes / hobby , but appears to be the only option for my use
I will look for the link , or somebody will post it ?

[davidefa]

I remember because is a nice idea ( no need to cut the traces to measure current ) but needs 'calibration'. Bandwidth is DC-5MHz, current 20A pk-pk

http://www.saelig.com/product/PSBEA014.htm

[nctnico]

Dave did a video on a current probe , it was a one of a kind I thought , and it did not use a loop of wire for measuring , it had a tip and would measure off traces .
The biggest thing relative to this thread is that it didn't cost $2,000+++ and dedicated to 1 scope .
If my memory is correct is was made in England and cost about $850 , high for my tastes / hobby , but appears to be the only option for my use
I will look for the link , or somebody will post it ?

You do know I sell a current probe for much less? You have to feed the current through it though.

[KD0CAC John]

How would I know , I do not see any mention of it in this thread , of course I could have missed it , I did look after seeing this post .

Dave did a video on a current probe , it was a one of a kind I thought , and it did not use a loop of wire for measuring , it had a tip and would measure off traces .
The biggest thing relative to this thread is that it didn't cost $2,000+++ and dedicated to 1 scope .
If my memory is correct is was made in England and cost about $850 , high for my tastes / hobby , but appears to be the only option for my use
I will look for the link , or somebody will post it ?

You do know I sell a current probe for much less? You have to feed the current through it though.

[nctnico]

Shameless plug then  :
https://www.eevblog.com/forum/buysellwanted/fs-new-cp2100-low-cost-current-probes-%28dual-channel%29/

edit: Or you could buy a clamp-on current probe from China:
http://www.ebay.com/itm/CP-07C-AC-DC-Current-Clamp-Probe-/121124596132

[kaz911]

Thanks to all for the good input!!!

I know sometimes giving a probe of 2kUSD to a student sounds crazy but we have good students  and if you are designing a power supIply a current probe with a bandwidth of 100kHz ... it is like measuring DC...

What i like of the probe RP1002C is that it uses a simple ac-adapter as power supply, so actually very cheap.

When I saw the prices of the dedicated power supplies for more professional probes (20+MHz) i wondered why they are so expensive. Most of the time the voltage tolerance is 12V+-0.5V with a current of about 0.5A or a bit more. In theory you could design a very simple power supply, and if you want even linear, that would match the specifications.

Of course I guess finding the connector it is a real challenge .

Definely the ucurrent project it is a bit too low... we usually range easily up to 30A.

In my previous job i used Tektronix MSO 4000 series and now LeCroy, both they have current probes up to 150A that they do not require external power supply but of course u can you them only with their scopes.

I understand having a power supply for powering the current probes and differential probes but it cannot be as big as the oscilloscope!!! -_-

We have some Rogowski coils for measuring ac-current up to 20MHz, they are just great (battery+ac-adapter), just missing dc...


I think I will have a look at the Fluke current probes, definitely interesting.

Rigol and Agilent seems to be using Hioki in the current generation of power supplies. On the probe-side the connector is the LEMO: FFA.0S.304.CLAC42Z Half Moon connectors (Citron maane for danskere) - but I would double check anyway - but the "original" probe power suppliers are the Hioki 3272 or Hioki 3269. But they are all about the same price from Agilent, Hoiki and Rigol.

The probe power supply should be able to supply +/- 12v 600mA for each probe attached.  Pinouts on page 3 in this pdf  - http://www.ltm.as/components/com_redshop/assets/document/extrafields/CLAMPE4-8ZM.pdf

But please double check before doing anything... The above is just from quick glances

[riccardo.pittini]

Thanks the last post is a great tip!!!

I do not understand how a power supply that provides +-12V and a bit more than 600mA on 4 channels could cost 1kUSD!!! -____-
I understand noise immunity and whatever... but still is about half the price of a decent current probe.

The other funny thing is that they use LEMO connectors (expensive connectors but very high quality).


The Rigol DS4000 series has the pin interface that can provide +-5V then maybe with a small monolithic dc/dc boost up to +-12 V and a 3D printed case could power the probe directly from the scope but I have to investigate the maximum power available form that pins ...

[banned 2017.08.31 12:44]

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Cheers