[volt-nuts] Traveling Standards

Charles Black cblack at centurytel.net
Wed May 9 01:49:02 UTC 2012

   Hi Randy,
   On 5/8/2012 2:19 PM, Randy Scott wrote:


That's very interesting information.  A couple of things that I'm curious about:

1. What is your typical TEMP? reading when your external sensor reads 23C?

   It was 36.67 last time I did a DC CAL at 23.0 +/- 0.2C. That was
   several weeks ago so it would be higher now. The sun has warmed the
   room to 26C and TEMP? is 41.3 now. When I got the unit the last CAL was
   done at 39.77C so I guess that the cal lab didn't bother cleaning the
   filter or maybe the room was warmer than 23C.

2. Do you see any difference between averaging 10 readings w/ NPLC=100
versus 1 reading w/ NPLC=1000?  That is, if I want to spend a given amount of
time taking a measurement, does it make any difference to let the 3458A do the
averaging over a longer integration time or can I just average multiple readings
with a shorter integration time?

   I haven't tryed averaging since just using NPLC = 1000 is simpler and a
   bit faster and thoroughly checked out. It takes about 33 seconds per
   reading. The end result would mathematically be the same though.

3. Have you see any unusual change in output immediately following
ACAL?  I haven't
investigated it thoroughly, but I'm seeing a slight increase in DCV
readings immediately
following an ACAL.  The offset goes away after a few minutes .  See
the attached plot
(with ACAL DC every 24 hours, measurements every 30 minutes, spikes are clearly

   Settling errors for DC volts are specified for the 3458A as 0.0001% of
   the input voltage step and HP wrote that it's due to source impedance
   and dielectric  absorption. I don't use early data after ACAL or range
   changes since it takes some time for my 3458a to reach equilibrium. The
   Agilent 3499 switch requires a delay each time a new input is made to
   allow for settling especially for 4-wire ohms.



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