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Accurate Low Amp Current Probe Advice

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KungFuJosh:

--- Quote from: Martin72 on November 12, 2024, 08:59:35 pm ---The electrolytic capacitors in my 503 module are all from Nichicon.

--- End quote ---

Mine only had Nichicon for the 220uF and BP 1uF. The rest were a different brand I can't remember right now. 3 letters, CFE or something like that. I think Mark's was the same with 2 brands.

My 503 is all Nichicon and Panasonic now (I went with whatever had better specs).

KungFuJosh:
Thanks to the Tek group, I found the correct values to make the pass through and voltage adapters for calibration (doc attached).

What I did was:
Pass through adapter:
Short M + N, also a 15kΩ coding resistor is connected between pins 'B' and 'K'.

Voltage adapter:
BNC terminated to pin 'M' on an Amphenol 165-9 or equivalent (I used 165-9-1000) connector. The shield of the coax is connected directly to GND pin 'J'.  A 1.13kΩ coding resistor is connected between pins 'B' and 'K'.

In my photo there's a 50Ω terminator at the end of the BNC cable, which is all it needs to avoid the 266 error code.

Degaussing was successful, I'll try doing the lower mV calibration later.

Thanks,
Josh

Martin72:
We do have some Tektronix stuff that was bought in the 90s.
What I didn't know, but discovered today, was that
we also have all the original documentation that was available at the time.
And the manuals look like they were filed yesterday. 8)
AM503B:
Tektronix Germany has no documentation other than the one already known.
I'll try again at Tek U.S.

KungFuJosh:
I was able to do the calibration. The lower levels both improved, but I made the 1A range slightly worse. I'm going to do a stability test now that I've done this and replaced the 1uF cap with a higher quality BP cap. When I do redo the calibration, I'll probably reverse the DMM setup so I have more digits for the spreadsheet.

I will probably toy with calibration more in the future, but the 1A+ range isn't that interesting to me, so  there's no rush.

Thanks,
Josh

KungFuJosh:
I've been screwing around with calibration more, and have noted the following things:

- It's best to work on one range at a time.
- Getting the source current to a far higher accuracy than suggested is helpful.
- You have to reset back to 61A8 before readjusting, which makes the process slightly more tedious.

I've found, at least with my setup, getting the negative values more accurate to be more challenging. I'm going to try the sequence again and see if I can get my starting numbers better.

For the record, this is entirely silly. The goal is to be within 1.5% margin of error... I started with the 1mA range at 0.326%, and got it to 0.305%, but want it better than that.

I was able to get the 10mA range to 0.006%. Supposedly. 😉

Thanks,
Josh

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