Tektronix A622 current probes - el (not so) cheapo clones.

[hibone]

Dear all,

while looking for a second hand A622 current probe, or an equivalent one, I found oh so many clones out there.

Among them I can remember the Agilent 1146B, Chauvin Arnaux E3N (SL261), Fluke 80i-110s, as well as the (not so clone but almost) Pintek PA-622 and the Wellzion PT-710 and PT-710A.

I also found a tear down of the chauvin arnaux model...


... and a meltdown of the Fluke one...
http://www.niell.org/DeadProbe/deadprobe.html

The cheap no brand models can cost about 280 €/$, thus, I was wondering if they are worth the while or if they may be fake. Does anyone has/had the chance to open a no brand clone apart?

Also, if the clones are the real thing, I wonder if it is possible to buy them at lower price, let's say down to 150 usd. I bet many users in this forum will appreciate that as well.     

Regards

[scopeman]

The Tek and the HP/Agilent/Fluke and any reputable  major test company that uses these buys them from Chauvin Arnaux as the AEMC (SL261) and they are rebranded Tek/HP/Fluke,etc. I think that the HP/Agilent ones are built in gray plastic cases instead of the standard black.

I have the schematic for this probe somewhere. When I find it I will post it. They are great probes.
They will also repair and recalibrate re-branded SL261's at a reasonable cost. IIRC it is a fix all flat rate.

I plan to add a bandwidth switch to one of mine to cut the bandwidth down as that will make it easier to make lower current measurements.

As a rule AEMC makes pretty good stuff. I have one of their small Rowgowski coil probes that I use on a 200KHz power amplifier. They are very reliable as long as you don't forget to change the battery!

Good company that I would not hesitate to recommend.

Sam
W3OHM

[artag]

I'd be interested to see that schematic.

I have one of these probes and it works well. The only snag is it's easy to leave them switched on, so if you don't use them often, take the battery out. They're often available much cheaper than the Tek branded ones, because ebayers don't realise they're the same thing. Though perhaps there is a difference : according to that video, it rattles and the Tek one doesn't. Mine rattles too. Maybe the tek one has a little bit of goo in it to stop it.

I have an almost identical probe (type E14), also made by Chauvin Arnoux, apparently for a 3-phase analyser that they sell. (That rattles, too). It's only marked as AC and has no zero adjustment. However, I think it has exactly the same hall-effect measurement system because it has a bandwidth that's more or less flat down to about 1Hz. I think it's the same thing, but with a DC blocking capacitor and no zero adjuster.

Since AC current probes are always cheaper than DC, especially secondhand, there's a bargain here if you don't need 0Hz.  It may even be possible to remove the capacitor, add the pot, and operate it down to DC.

[HighVoltage]

I have the schematic for this probe somewhere. When I find it I will post it.
Sam
W3OHM

I really would appreciate a copy of that schematic and if possible, a service manual.

These are really great probes.
I have several of them in different branding and I have not seen any differences between them.

Instead of a battery, I use rechargeable, then its not such a pain, when you leave them on.
 

[scopeman]

I am curious what brands other than HP/Fluke/AMEC/Chauvin Arnoux you have seen these probes under.

Now for a dog ate my homework story.....

I went to dig up the schematic today and spent time getting a new power supply for my computer. I turned it off before the USA East Coast "Snow Armageddon" on Friday and when I went to turn it on this morning nothing happened. Probably bad caps but no time to fix it. It ran for 10 years so I really can't complain.

In any event I should have the machine up tomorrow and I will look for that schematic.

Sam
W3OHM

P.S. We had a strange event at work today. Three of our large windows that look out the front of the building cracked.  We believe that it was due to the snow load on the roof! One of my colleagues was in his office when one went pop! Just has a hairline crack all the way across in the horizontal direction (but not a straight line).

[scopeman]

I found the service manual. See attached.

It appears that they use the hall effect sensor for the full bandwidth which is different that the ingenious Tek approach. The venerable P6042 comes to mind where the Hall is used for DC and LF AC and there is a separate current probe coil wound on the same core  (as used for the hall sensing) that forms a 50MHz current probe.

The probe amplifier combines the hall output and the probe coil output so that the bandwidth is flat from DC-50MHz. I have not looked into the A622 core material permeability past the 100KHz bandwidth but maybe the probe could have a coil/summer amp added to extend the bandwidth somewhat.

I think to get to the frequencies that the P6042 can cover you will need much smaller probe geometries. There was a time when you could pick up P6042's for 100 bucks but I have not seen them that low recently (almost as if Dave reviewed them!). Repairing the amplifier can be tricky.

One other DC current probe/meter that I really like (I have several) is the Hewlett-Packard HP-428B. It covers 1mA to 10A full scale and has a front panel output jack that you can use with a DMM and/or scope for a bandwidth of DC-400Hz. Unlike most DC probes it uses the flux gate principle.

Sam
W3OHM

P.S. I would have attached the HP428A article and the manual but they both exceed the file attachment size limit. If you send me a PM I will send you copies by email.

[artag]

Thanks !

No obvious DC/AC version, though there's a zero ohm resistor that could easily be replaced with a capacitor in the output lead. I'll have to take my AC probe apart and see how it differs.

That's an unusual bit of circuitry driving the battery check LED.

[scopeman]

The Battery Check to me seemed like overkill. I think it could have been done with a TL431.

Sam

[HighVoltage]

I found the service manual. See attached.

Thank you for the service manual.

[harrimansat]

Hi, can someone check how much current this thing drains when switch is off position? Mine drains 0.5 mA.

[shakalnokturn]

A bit late I think but just for the records:
No measurable current draw in OFF position.
Draws 7mA @ 8.5V when on.

I have one of these with a dead hall sensor (one terminal open).
In the technical documentation provided above the hall sensor is identified (in the schematic only, not in part list) as a HW-300B-E (AKM).
I ordered and received some of these from Aliexpress, they look genuine perform like linear hall sensors, marking and package dimensions conform to the attached AKM datasheet.
However the hall sensor originally fitted to the current probe does not have the same dimensions, it's 2.7x 2.3x 0.9mm where the AKM part is 2.7x 2.9x 1.65mm.
Original sensor has nothing readable on it (but it was held in glue) one side is coloured blue.

The sensor is sandwiched in a plastic housing that then fits into the magnetic core, it's all a very tight fit so I've had to sand two sides of the sensor to get the whole assembly to fit back into the core. Now the clamp is working but I have too much gain even with the multi-turn trimmer at minimum so I'm going to have to work around that too...

So I don't really believe that they used the part number stated in the schematic, at least not on all models... Any clue what other sensor they may have used ?

[shakalnokturn]

I ended up changing the gain at the differential amplifier to get the gain trimmer back in a useable range.
Readjusted at DC, then thought it would be interesting to see how it performed in AC.
Test setup is a function generator into a HK6150 audio amplifier with 10 Ohms worth of load.

Channel 1 yellow:
1 Ohm resistor for reference measurements.
Channel 2 cyan:
LEM HEME PR30 (first edition with only 100mV/A position)
Channel 3 magenta:
Stock Tek A622
Channel 4 green:
Repaired Tek A622

I pushed this about as far as the audio amplifier would go just to see how the PR30 would cope.

The main conclusion is that the PR30 doesn't rely solely on a hall sensor...