The offset adjustment R317, is an AC adjustment, not DC as one might
surmise. As I recall I applied a 10X scope probe to the O/P point at
the junction of R329 and R330 to view the AC component. I probably used
a 10Meg ohm with a cap in parallel, in a well shielded enclosure across
the input jacks. I probably set the 1281 to the 10V range.
As for R222 the input bias, I think I just barely touched up the
adjustment so that there was little drift with the input open. That is,
the input would float around a low displayed value, and climb to a large
number in either polarity.
I paraphrased the adjustment info from the 1081 and applied it as much
as possible to the 1281.
Another thing I learned from owning two, and working on a few more
1281's is that the first thing to do is replace all the aluminum
electrolytic caps on the analog board as a minimum. Especially the small
1uf caps on the 3-terminal regulators die and the noise increases. This
will cause all kinds of problems. I change them all, on all the boards.
Due to the low profile of the larger caps careful selection is necessary.
A few years ago I had email contact with one of the technicians at Fluke
Farnborough, the home of the 1281. He wasn't much help, but
indicated that internal adjustment procedures were never released. He
wouldn't provide any details either..
Sorry for the nebulous response, but it has been awhile since I adjusted
mine.
Bob Koller
On 5/23/2015 9:00 AM, [email protected] wrote:
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Today's Topics:
1. Datron 1281 offset null, Bias current adjustments
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2. Datron 1281 offset null, Bias current adjustments
([email protected])
3. Re: Datron 1281 offset null, Bias current adjustments
(Electronics and Books)
----------------------------------------------------------------------
Message: 1
Date: Sat, 23 May 2015 04:38:48 -0400
From: <[email protected]>
To: Discussion of precise voltage measurement <[email protected]>
Subject: [volt-nuts] Datron 1281 offset null, Bias current adjustments
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
I have a Datron 1281 DMM.
How to set the bias current adjustment (R222)?
How to set the offset null adjustment (R317)?
Thanks,
John Staron
------------------------------
Message: 2
Date: Sat, 23 May 2015 04:39:52 -0400
From: <[email protected]>
To: Discussion of precise voltage measurement <[email protected]>
Subject: [volt-nuts] Datron 1281 offset null, Bias current adjustments
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8; format=flowed
I have a Datron 1281 DMM.
How to set the bias current adjustment (R222)?
How to set the offset null adjustment (R317)?
Thanks,
John Staron
------------------------------
Message: 3
Date: Sat, 23 May 2015 10:41:09 +0000 (UTC)
From: Electronics and Books <[email protected]>
To: Discussion of precise voltage measurement <[email protected]>
Subject: Re: [volt-nuts] Datron 1281 offset null, Bias current
adjustments
Message-ID:
<[email protected]>
Content-Type: text/plain; charset=UTF-8
offset
looking at the schematics on page 11.2-3 the bias should be adjusted by
shorting the inputs of the amplifier and then a zero output.
biasshorting the external input and measure the output of the amplifier
i could not find the internal adjustments in the manual.
Met vriendelijke groeten
Regards
Frans
http://ElectronicsAndBooks.com
Netherlands
Discere ne cesses
From: "[email protected]" <[email protected]>
To: Discussion of precise voltage measurement <[email protected]>
Sent: Saturday, May 23, 2015 10:39 AM
Subject: [volt-nuts] Datron 1281 offset null, Bias current adjustments
I have a Datron 1281 DMM.
How to set the bias current adjustment (R222)?
How to set the offset null adjustment (R317)?
Thanks,
John Staron
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