Products > Test Equipment
Accurate Low Amp Current Probe Advice
KungFuJosh:
--- Quote from: nctnico on November 10, 2024, 10:47:08 pm ---The date codes on various seem to suggest your unit was manufactered after 1995. What date does it say on the 'tested' sticker? Interestingly, I'm using the same stickers BTW.
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That's almost 30 years. I said 37 based on the copyright on the PSU board. The PSU is older than my AM503B. There's a Copyright 1993 marked on the AM503B. Neither are young. 😉
MarkL:
--- Quote from: KungFuJosh on November 10, 2024, 06:19:08 pm ---
--- Quote from: MarkL on November 10, 2024, 05:48:12 pm ---I'll run the same stability test on the second AM503B in the next day or two for curiosity's sake. You're right that there might be other differences between the two. One test could be adding the cap to the first, or removing it from the second. But if they're both equally stable, I'm probably not going to mess with either.
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If one is more stable than the other, I'd start with the big 4 caps with low ESR versions like I used. Those had a bigger impact than anything else so far.
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Was your measurement technique consistent in your comparison? You had swapped in the DMM in place of the scope at some point.
I would expect the large filter caps to affect noise and not so much the slowly changing DC drift.
--- Quote ---Is your 1uF cap bipolar?
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Yes, on both units.
nctnico:
--- Quote from: MarkL on November 10, 2024, 11:02:58 pm ---
--- Quote from: KungFuJosh on November 10, 2024, 06:19:08 pm ---
--- Quote from: MarkL on November 10, 2024, 05:48:12 pm ---I'll run the same stability test on the second AM503B in the next day or two for curiosity's sake. You're right that there might be other differences between the two. One test could be adding the cap to the first, or removing it from the second. But if they're both equally stable, I'm probably not going to mess with either.
--- End quote ---
If one is more stable than the other, I'd start with the big 4 caps with low ESR versions like I used. Those had a bigger impact than anything else so far.
--- End quote ---
Was your measurement technique consistent in your comparison? You had swapped in the DMM in place of the scope at some point.
I would expect the large filter caps to affect noise and not so much the slowly changing DC drift.
--- End quote ---
I probably missed this but are there any schematics available? The only cause for slow drift I can think of where it comes to electrolytics would be leakage current. But this would mean the large capacitors would be part of some kind of (slow) servo mechanism. Maybe to cancel DC magnetic field in the probe head? The schematics should tell what is what.
KungFuJosh:
--- Quote from: MarkL on November 10, 2024, 11:02:58 pm ---Was your measurement technique consistent in your comparison? You had swapped in the DMM in place of the scope at some point.
I would expect the large filter caps to affect noise and not so much the slowly changing DC drift.
--- End quote ---
Yeah, I left everything setup exactly the same. Nothing was moved.
The initial change from 4.5mV to 0.2mV was done using the scope. Test 3 with the DMMs was 0.236mV over a longer period (see attached, and note the names displayed for each device). The only change was the 4 larger caps in the 503B at the time.
--- Quote ---
--- Quote ---Is your 1uF cap bipolar?
--- End quote ---
Yes, on both units.
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Thanks!
KungFuJosh:
--- Quote from: nctnico on November 10, 2024, 11:09:15 pm ---I probably missed this but are there any schematics available? The only cause for slow drift I can think of where it comes to electrolytics would be leakage current. But this would mean the large capacitors would be part of some kind of (slow) servo mechanism. Maybe to cancel DC magnetic field in the probe head? The schematics should tell what is what.
--- End quote ---
There is no known publicly released schematic for the AM503B. The AM503A might be similar enough for those parts though.
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