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Test Equipment Anonymous (TEA) group therapy thread

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bd139:

--- Quote from: Cerebus on May 18, 2018, 05:35:50 pm ---
--- Quote from: bd139 on May 18, 2018, 04:50:17 pm ---These are 100% works or doesn't work instruments.

--- End quote ---

Not entirely. The resistance ranges can be knackered with the rest working fine. I don't know why, in principle there's nothing obviously wrong with the designs, but HP always had problems with the current sources on resistance ranges. If you've an HP34xx and everything's working perfectly except resistance then it's always the current sources. It's a stock fault for HP meters.

--- End quote ---

Fair point but those are usually massive errors and these meters checked out close to spec before sending off for cal.

Edit: plus they had recently expired Keysight own calibration stickers all over them.

Specmaster:

--- Quote from: bd139 on May 18, 2018, 04:50:17 pm ---Yep. Divs.

It's not even analogue to cal it. You just:

1. turn the switch
2. stick it in the range you want to cal
3. short it.
4. press the cal button
5. apply 1/3rd scale (not even required on all ranges)
6. adjust the display to the calibration voltage if you need to.
7. press cal.
8. goto 2.

Eventually when you've done them all it'll start up with SELF TEST OK  :-//

If it's reading low, it's basically a Y=MX+C transform where M and C are calibration variables. So someone put the wrong fucking M or C in.

When I did mine I did it with a PSU and connected the U1241 in series (current) or parallel (voltage) to it. Resistance I used some 1% resistors and frigged the display value to match the U1241's interpretation of the value. The linearity is amazingly good so was spot on when I cranked it up near FSD.

These are 100% works or doesn't work instruments.

--- End quote ---
That is my understanding of it as well, basically give it a known value and adjust the display by using the up and down arrow till the display reads the known value and press CAL which can mean holding the respective button in for a very long time to reach the desired reading, this is the reason why I did not decide to it myself using the method that you describe. I assumed that a proper calibration house would have short cuts to a way of dialing in the correct reading using the GPIB or something that we mere mortals do not have access to?

I must admit I have not RTM fully for that section but I assumed that the resistance would more or less fall into place once the DC voltage has been done as surely most meters are just reading the voltage drop across the load?

ACV does that have its own adjustment if so then that might be where I'd struggle if doing it myself as I don't have an accurate source voltage unless a variac is considered good enough.

I have the MS7221 coming early next week that will provide pretty reasonable DC voltage standards and also current unto 24mA so if all else fails I'll have a go myself  :palm:

bd139:
It only requires one AC V I think. Was 3v. I used a function generator and connected U1241C in parallel.

Specmaster:

--- Quote from: bd139 on May 18, 2018, 05:46:44 pm ---
--- Quote from: Cerebus on May 18, 2018, 05:35:50 pm ---
--- Quote from: bd139 on May 18, 2018, 04:50:17 pm ---These are 100% works or doesn't work instruments.

--- End quote ---

Not entirely. The resistance ranges can be knackered with the rest working fine. I don't know why, in principle there's nothing obviously wrong with the designs, but HP always had problems with the current sources on resistance ranges. If you've an HP34xx and everything's working perfectly except resistance then it's always the current sources. It's a stock fault for HP meters.

--- End quote ---

Fair point but those are usually massive errors and these meters checked out close to spec before sending off for cal.

Edit: plus they had recently expired Keysight own calibration stickers all over them.

--- End quote ---
No mine didn't have those stickers on it as I removed them as part of the cleaning operation but is calibrated by Keysight in Jan 2016 same as yours and they were able to tell me that it was calibrated about 18 months ago. A 10K 1% resistor was reading 10,0014.3 \$\Omega\$ so yes its was just about spot on before the battery shorted out for a split second.

Specmaster:
The fact that they were not instantly aware of the 3478A at the time of requesting a quote etc is now beginning to gnaw at me that they probably do not understand how to do it and either looking for manual adjustment pots or maybe the more modern meters are just a matter of plugging a source in and then telling it via a computer interface what the value of that source actually is and they weren't that far advanced when the 3478A's were made?

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