Three HP3468A's vs four other voltmeters

[intabits]

I found this interesting...

Before trying to read the calibration data stored in the battery backed RAM of my HP3468A multimeters, I wanted to get an idea of their current calibration state.

Here they are connected in parallel with two HP3456A's, an HP3455A, and a Fluke 8800A. I used some cheap ebay AD548 voltage reference modules as the measurement source.

While their readings are within spec, they do not agree with each other very well, nor with the other four meters, which are in very close agreement.

Nominal 2.5v from AD5484#1 (no "calibration certificate")


Nominal 5v from AD5484#2 (also no "calibration certificate")


AD5484#4 calibration certificate says it should be 10.0032v

[coromonadalix]

Witch meter in the loot as an recent calibration    One meter as to be recently calibrated and serve as a reference for the others ...

[Kleinstein]

The 3468 like the very similar 3478 and the higher grade 3457 have ranges of 300 mV/3 V / 30 V /300 V.
So the 5 V and 10 V are already using the input divider and are not that accurate in this range. The 2.5 V is more suited for these meters. The difference could be from a common aging part, a all using the same cal source that was a bit off.

It is an odd internal construction (e.g. no range without gain at the input stage) and never meant to be highly accurate. They are still nice 5.5 digit meters, as the have good resolution in the 30 mV range.