Hi guys,
I bought an HP 3458A, backed up the calibration memory and put it through the standard checks. As far as I can tell the voltage/current range is accurate, but the resistance is off by quite a bit.
As a known resistance I have used a 0.005% 100 Ohm resistor (Vishay PG VFR). The measured value by a 6.5 digit DMM was 100.0005 Ohm and can be assumed to be accurate.
The 3458A measures:
100 Ohm range: 099.93925 Ohm
1 kOhm range 0.0999389 kOhm
So, something's off. After looking at the calibration table I got by the awesome GPIB utility (
https://xdevs.com/article/hp3458a_gpib/#calgpib ) I saw the following line:
19:41:24 60000 - 39,972.9570342778 (39,997.51395) - 40K reference19:41:24 60008 - 7.11940040146345 (7.170674313) - 7V reference
Now, the 40k Reference resistor (I assume) is quite different from the typical value (in brackets). They have a ratio of 1.0006143382 . Now, here's the funny thing:
Multiplying the measured 99.93925 Ohms by the ratio gives me 100.0006465021 Ohms - which is much closer to the (assumed) real value of the measured resistance.
So, somehow, the calibration got messed up or switched, or done wrong? It seems that the typical value should be the one in the calibration. What could have happened? Wrong calibration procedure?
Also, I've been looking into the other lines of the calibration. These look a little worrying:
19:41:24 60626 - 73 (27) - Destructive Overloads
19:41:24 6062A - 2,920,366,096 (0) - Defeats
First of all, shouldn't 'destructive overloads' me 0 or borked? Also, what does the Defeats line mean? Mine seems to have had a lot of them. Whatever they are...
Thanks guys,
David
Note: All resistance measurement was done 4W.