Author Topic: 3458A CAL & repair  (Read 3582 times)

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Offline ap

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Re: 3458A CAL & repair
« Reply #25 on: March 27, 2018, 06:39:59 pm »
The zero-calibration cannot compensate the high zero-ohms value you mention, it would show a calibration out of range error (which makes sense, because you never have a two-ohm-ish reading between binding posts and card input, this indicates an error). So the activation of the switch must have changed that (as is often the case). The internal wiring thus can most likely be excluded (it was not changed, and the meter seems stable now). I would just watch it over time, and you can then make a justified decision later to exchange the switch (or do it anyway, even though thats not a long term guarantee if the new switch is not toggled from time to time).
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Online Dr. Frank

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Re: 3458A CAL & repair
« Reply #26 on: March 27, 2018, 08:35:47 pm »
Adrian, you're right.
The limits of the 10 Ohm range are: CAL? 13,3 = 1,0192 Ohm, and are the  same for front and rear, and for 100 Ohm range, of course.
I think, it's not possible to calibrate zero, if the switch contact resistance is constantly beyond these limits, or KS has the magic command to overdrive this.

I just just checked my 3458A, the calibrated resistance is about 310mOhm, which is already quite high.
The zero value, using that copper wire on the jacks, gave about 50mOhm.

Then I actuated the front/rear switch, and got > 1.5 Ohm in first instance, but not stable, instead quickly falling below 200mOhm again.
Only after 30 actuations, the resistance was again at about 50mOhm, stable reading even after a further actuation.. strange behavior..

Ian might check the calibrated zero value, i.e. CAL? 13 and CAL? 22.

If KS also simply actuated the front/rear switch several times to get the initial reading below 1 Ohm, and getting this stable also, then I don't understand why they made this conditional calibration, and set several modes to UNDETERMINED, in a random manner, obviously.
Makes no sense to my opinion.

Maybe Ian can also ask KS, what happened there..

Frank
 

Offline IanJ

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Re: 3458A CAL & repair
« Reply #27 on: March 27, 2018, 09:55:14 pm »
Hi,

Yes I'll ask KS......and I'll also point them to this thread.....and I'll also look at the cal zero vals when I get back to the workshop later tonight.

For me, I don't care about the rear switch and wish there was a relatively easy way to by-pass it all and remove the switch, wiring and rear posts completely......and of course which would still allow KS to cal the meter in the future (wouldn't want them to say "modded meter huh?...no thanks").
It's a failure mode I would just like to see the back of......and if I had a 2nd 3458A I'd be looking into this even if it meant designing a proper PCB/loom to change it out. Hmmmm thinking about that, Adrian, if you have a used A10 assembly for sale then let me know.

Ian.
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Offline TiN

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Re: 3458A CAL & repair
« Reply #28 on: March 27, 2018, 10:15:17 pm »
I just checked on my rusty friends. 311 mOhm and 353 mOhm for CAL? 13,1.
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Offline ManateeMafia

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Re: 3458A CAL & repair
« Reply #29 on: March 27, 2018, 11:05:25 pm »
It would be interesting to know how Keysight handles calibrations on meters where the pushrods have been removed to prevent the switch positions from being moved.
 

Offline IanJ

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Re: 3458A CAL & repair
« Reply #30 on: March 29, 2018, 03:46:22 am »
Adrian, you're right.
The limits of the 10 Ohm range are: CAL? 13,3 = 1,0192 Ohm, and are the  same for front and rear, and for 100 Ohm range, of course.
I think, it's not possible to calibrate zero, if the switch contact resistance is constantly beyond these limits, or KS has the magic command to overdrive this.

I just just checked my 3458A, the calibrated resistance is about 310mOhm, which is already quite high.
The zero value, using that copper wire on the jacks, gave about 50mOhm.

Then I actuated the front/rear switch, and got > 1.5 Ohm in first instance, but not stable, instead quickly falling below 200mOhm again.
Only after 30 actuations, the resistance was again at about 50mOhm, stable reading even after a further actuation.. strange behavior..

Ian might check the calibrated zero value, i.e. CAL? 13 and CAL? 22.

If KS also simply actuated the front/rear switch several times to get the initial reading below 1 Ohm, and getting this stable also, then I don't understand why they made this conditional calibration, and set several modes to UNDETERMINED, in a random manner, obviously.
Makes no sense to my opinion.

Maybe Ian can also ask KS, what happened there..

Frank

Hi,

I have just this minute modified my macro (Win7 Excel) to get the CAL? vals, as follows.......PS. Haven't formatted the results yet:-

CAL? 13   = 523.461471E-03 (0.523461471)
CAL? 22   = 438.050474E-03 (0.438050474)

Whilst at it:
No. Times Calibrated = 51
3458A temp = 40.5 (my 3458A is on 24/7 and is in a room at 24-25degC)
Error register = 0

Ian.
« Last Edit: March 29, 2018, 06:27:35 am by IanJ »
Ian Johnston
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Manufacturer of the PDVS2
 

Online Dr. Frank

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Re: 3458A CAL & repair
« Reply #31 on: March 29, 2018, 07:02:09 am »
So KS could have done a proper calibration. Switch is not fresh, but may have been rejuvenated by frequent actuation.

Clean your fan, please. Also frequently, because of 24/7.
13°C difference is clean, 15-16°C means wool mice = dust bunny.

Frank
« Last Edit: March 29, 2018, 07:05:50 am by Dr. Frank »
 
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