Hi Paul,
On 11/04/2014 19:18, Poul-Henning Kamp wrote:
In message <[email protected]>, Tony writes:
I did find this explanation in the 3458A manual:
When making DC voltage measurements, you can fix the multimeter's input
resistance using the FlXEDZ command. This is useful to prevent a change
in input resistance caused by changing ranges) from affecting the
measurements.
Please don't forget that the 3458A is not just an 8.5 digit
metrological wonder, it is also a precision 16 bit 100 ksample/s
digitizer.
Yes I'm well aware of that but it doesn't make any difference if you're
observing the display or the logged data - you would not want that 10M ±
1% resistor across the input - unless you have no choice because the
input exceeds 12V and you have to use a 100V+ range, in which case you
have to accept the limitations of the instrument. I accept that it could
help in some situations where you aren't bothered about absolute
measurements but are interested in changes and the resistor helps to
reduce the noise.
In such a situation I agree you would probably be logging the data
rather than looking at the display but the sampling rate has no bearing
at all on this issue.
Many of the attributes of the input circuit are not there for
voltage metrology.
I can't think of any - I'd be interested to know what you have in mind?
Regards,
Tony H
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