[volt-nuts] Fluke 887 mod with LTC1050

Randy Evans randyevans2688 at gmail.com
Thu Apr 27 20:02:41 EDT 2017


You are absolutely correct.  I misread the data sheet.  It's interesting
that all three LTC1050s behave exactly the same. They have the same lot
code number.but I would expect more variation.  Live an learn.


On Thu, Apr 27, 2017 at 12:18 PM, Charles Steinmetz <csteinmetz at yandex.com>

> Randy wrote:
>  but I recently noticed the meter reads -0.08 when the
>>  input is open on the 1V range and the null switch is on 0.0001
>>  This equates to a -8uV reading.
>>  I believe this is due to the input bias current of the LTC1050
>>        *   *   *
>>  However, this would imply an 8pA bias current,
>>  which is much higher than expected.
> I am attaching the relevant portion of the LTC1050 datasheet.  Note that
> at 25C, the 1050 has an input offset current spec of +/- 20pA (both typical
> -- max is ~5x worse).  I would expect a total input offset of +/- 20uV
> (typical) in your circuit.  (The 0.5uV typical input offset voltage is not
> a significant contributor in this context.)
> Best regards
> Charles
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