Re: [volt-nuts] Fluke 887 mod with LTC1050

[Randy Evans]

It looks like a better candidate would be the LTC2054, which has a typical
bias current of 1 pA at 25C and is essentially constant up to 45C.

Randy

On Thu, Apr 27, 2017 at 5:02 PM, Randy Evans 
wrote:

> Charles,
>
> 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.
>
> Randy
>
> On Thu, Apr 27, 2017 at 12:18 PM, Charles Steinmetz  > wrote:
>
>> 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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>
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Re: [volt-nuts] Fluke 887 mod with LTC1050

[Randy Evans]

Charles,

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.

Randy

On Thu, Apr 27, 2017 at 12:18 PM, Charles Steinmetz 
wrote:

> 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
>
>
>
> ___
> volt-nuts mailing list -- volt-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/volt-nuts
> and follow the instructions there.
>
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