[volt-nuts] HP3457 quirks and gripes

Brian Kirby kilodelta4foxmike at gmail.com
Tue Aug 4 00:52:46 UTC 2009


We'll, asking the 3457A to read 7.5 digits - exceeds the capability of 
the internal reference.  A 6.5 digit meter needs a reference to have 0.5 
ppm stability.  The service manual rates the instrument at 5 PPM, and 
when I had a cal lab to test my unit, it came back as 5.8 ppm.

Something else to remember, is the last digit of the multimeter should 
not really be used, if your concerned about accuracy.

A good application note to read on this issue is AN82-1 from Linear 
Technology.  There is a graph on the front page that sums it up.

Mark Sims wrote:
> My main gripe with the 3457A is that high-res mode.  It was just plain stupid on HP's part to not make the meter operate directly in 7.5 digit mode.  Why does one have to read a separate register and manually add it to the reading?  Come now... can't a microprocessor do that better than a person.  In fact I built a 3457A GPIB interface to a MegaDonkey touch screen LCD controller specifically to read the high res register and do the addition/display.
>
> Another thing to watch out for on the 3457A is the "seams" between the ranges.  Even on units freshly checked out and calibrated from HP I have seen rather large errors in readings when I put a precision resistance decade box or voltage cal source on the thing.  Stepping the value from say 2.9V to 3V  and from 3.1V to 3V produces different readings that were out of spec. (the 3V point seems the most error prone).
>
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