[volt-nuts] Fluke 887 mod with LTC1050

[Charles Steinmetz]

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


-------------- next part --------------
A non-text attachment was scrubbed...
Name: LTC1050_specs_sm.jpg
Type: image/jpeg
Size: 33085 bytes
Desc: not available
URL: <http://www.febo.com/pipermail/volt-nuts/attachments/20170427/52a6841b/attachment-0001.jpg>