Author Topic: 34401a range issue (Read 8352 times)

dohyun · « **on:** June 23, 2016, 12:05:28 am »

Howdy all,

I recently got a 34401a on ebay marked as "for parts" but thankfully all the self tests pass. However, I noticed a somewhat odd issue. When testing DC voltage with a 10V ref (from voltagestandard.com) I get a fairly large out of tolerance (though it is close enough to 10V to not be completely wonky). The odd part is, when I switch out of auto ranging and go to manual and step up to the 100V range, it is dead on accurate.

I am trying to figure out if this is a calibration only issue, or if something is off and I can fix it (kinda hoping for the latter)

I've measured as far as U102 input, and from the looks of it on U102 Pin 5, there is the still-solid 10V signal.

Has anyone ever run into something like this before? This is my first attempt at a DMM repair.

dohyun · « **Reply #1 on:** June 23, 2016, 01:28:22 am »

Err, I meant U101 there, not U102

dohyun · « **Reply #2 on:** June 23, 2016, 02:09:21 pm »

Additional info:

It looks like it is not just the 10V range, when testing against 1V and 100mv (using an additional borrowed 34401a) the DCV measurements in my 34401a are off for the 100mv, 1V, and 10V range, but a dead on match with the other 34401a on the 100V and 1000V ranges.

Andy Watson · « **Reply #3 on:** June 23, 2016, 02:14:57 pm »

Not an answer, but gathering more evidence: There is an option to operate the meter in either high-impedance mode, or 10M\$\Omega\$ input impedance on voltage ranges of 10V or less - does changing this option in the system menu make any difference?

dohyun · « **Reply #4 on:** June 23, 2016, 02:28:51 pm »

Thanks for the reply Andy.

I just tried that and the results didn't change between the 10M and high-impedance mode.

HighVoltage · « **Reply #5 on:** June 23, 2016, 03:09:20 pm »

Since you have a 10V reference, I would just calibrate the 10V only and see the result.

dohyun · « **Reply #6 on:** June 23, 2016, 03:24:23 pm »

Makes sense. I've got the Fluke 4 terminal shorting plug on order to zero adjust for the calibration and then will give that a shot. Will update with the result!

HighVoltage · « **Reply #7 on:** June 23, 2016, 05:23:20 pm »

Quote from: dohyun on June 23, 2016, 03:24:23 pm

Makes sense. I've got the Fluke 4 terminal shorting plug on order to zero adjust for the calibration and then will give that a shot. Will update with the result!

Even better.
Do the zero adjust first and then the 10V DC calibration only.
I had a corrupted storage chip before and it would not write the new calibration data.

bitseeker · « **Reply #8 on:** June 23, 2016, 06:42:03 pm »

I was about the ask for some actual values for those "fairly large out of tolerance" measurements (quantitative vs. qualitative). It sound like the meter just needs adjustment, but I'll wait to see the outcome of the zero and 10V calibrations.

dohyun · « **Reply #9 on:** June 23, 2016, 07:43:21 pm »

Since it will be a few days before the shorting plug gets here, here are some numbers:

10V ref calibrated (by an in-cal 3458A) at 10.00000V

When measuring the 10V ref in the 10V range I get 10.06887V however when I move up to the 100V range I get 10.0002V (which looks to be in tolerance for the 100V range)

bitseeker · « **Reply #10 on:** June 23, 2016, 08:53:22 pm »

That's out alright, but less than I was imagining for "fairly large". Looking forward to your post adjustment update.

dohyun · « **Reply #11 on:** June 25, 2016, 06:29:32 pm »

I think that did the trick. After zero calibration and calibrating the 10V range to the 10V reference it is looking consistent and solid.

Since it looked to be a calibration adjustment issue, I might take advantage of the $75 calibration w/ data deal from Global Test Equipment for some of the other functions which I am not as able to verify their performance.

All in all I think it was a worthwhile score, $157 (including shipping) for the "broken" meter and $35 for the fluke 4 wire shorting block.

But for now, things are looking great, thank you all for the help!

HighVoltage · « **Reply #12 on:** June 25, 2016, 07:08:35 pm »

Great news,
Before you send it out for calibration, keep it running for a few days to see the variation of your 10V standard and make sure you don't have a too large drift ind the 10V range. There must have been a reason for the range to be so far off.

Jwalling · « **Reply #13 on:** June 25, 2016, 08:05:21 pm »

Quote from: dohyun on June 25, 2016, 06:29:32 pm

I think that did the trick. After zero calibration and calibrating the 10V range to the 10V reference it is looking consistent and solid.

Since it looked to be a calibration adjustment issue, I might take advantage of the $75 calibration w/ data deal from Global Test Equipment for some of the other functions which I am not as able to verify their performance.

All in all I think it was a worthwhile score, $157 (including shipping) for the "broken" meter and $35 for the fluke 4 wire shorting block.

But for now, things are looking great, thank you all for the help!

Nice work, and a great price. Thanks for the info on GTE. I need to have a (repaired) 34970A calibrated that's had it's FRAMs replaced. Last time I had one calibrated it cost me $125 + return shipping. GTE covers the return shipping!

Jay

dohyun · « **Reply #14 on:** June 25, 2016, 08:49:47 pm »

Good call, I will keep it running for a few days and see if there is any more drift.

bitseeker · « **Reply #15 on:** June 25, 2016, 09:56:58 pm »

Congrats on that adjustment working out. Looks like you got yourself a great deal. Definitely see how well it holds over time before shelling out money for the full adjustment.

dohyun · « **Reply #16 on:** June 28, 2016, 11:49:03 am »

So far the measurements (from spot checking) have only varied from 9.99999 to 10.00003 over the past couple of days. However I am going to set up some automated measuring to watch it a bit longer before feeling confident enough to send it out for cal.

HighVoltage · « **Reply #17 on:** June 28, 2016, 03:34:41 pm »

That is already good news.
It seems you got very lucky with that instrument.
The variation you saw so far are very normal and can be contributed to temperature drift of the 34401A and the 10V reference

Jwalling · « **Reply #18 on:** June 28, 2016, 05:07:12 pm »

Quote from: dohyun on June 25, 2016, 06:29:32 pm

Since it looked to be a calibration adjustment issue, I might take advantage of the $75 calibration w/ data deal from Global Test Equipment for some of the other functions which I am not as able to verify their performance.

Hmm. They're not returning my emails. Did you try contacting them via email by any chance?

Jay

dohyun · « **Reply #19 on:** June 28, 2016, 05:11:10 pm »

Jay,

I did, I e-mailed tech-help@4gte.com asking if the promotion for $75 was still on, it took a few days but someone got back to me asking if I wanted to go ahead (and that yes the $75 deal was still on).

I will send you a message with the contact details of the person who directly replied to me.

bitseeker · « **Reply #20 on:** June 28, 2016, 06:06:14 pm »

Yep, the special is still on their site: http://4gte.com/calibration-and-repair/

Jwalling · « **Reply #21 on:** June 28, 2016, 07:10:18 pm »

Quote from: bitseeker on June 28, 2016, 06:06:14 pm

Yep, the special is still on their site: http://4gte.com/calibration-and-repair/

Hi bitseeker,

Thanks for that. The weirdest thing is that I didn't have to email again. He emailed me and said that I was caught in their spam filter, after buying a TDS5054B from me four minutes earlier.

Jay

bitseeker · « **Reply #22 on:** June 28, 2016, 08:46:39 pm »

Oh, that's a good one. At least they periodically check their spam folder. So, now you're mutual customers.

dohyun · « **Reply #23 on:** July 01, 2016, 08:33:16 pm »

Meter is on its way to the calibration folks. Thanks again for all the help. BTW, GTE gave me a heads up that one of their standards is going out for cal on 7/14 so anything arriving on or after that might be delayed for a few weeks.

bitseeker · « **Reply #24 on:** July 01, 2016, 11:54:48 pm »

Hmm, might be good to wait. Get a fresh cal from a fresh cal.


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Author Topic: 34401a range issue (Read 8352 times)

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