[volt-nuts] Just back from cal

[Joseph Gray]

In February, I sent my HP 3457A in for cal. In late March, I sent my
EDC VS330 DC Voltage Reference in for cal. Today, I just got the VS330
back and thought I'd compare the two instruments.

Both instruments have been on for a couple of hours. It is about 25 C
in the room.

Setting 10.00000 on the VS330, I measure 9.99891 VDC on the 3457A.

According to the manual, on the 30 VDC range, the 90 day spec is
0.0035% of reading, plus 19 counts.

The VS330 lists the "Limit of error accuracy" as 0.003% of setting
plus 0.001% of range (30 V range). The "Calibration accuracy" is
0.002% of setting plus 0.0005% of range.

Now, if we take the worst case for both instruments, what I am reading
is marginally inside the total error for both instruments. However,
considering that both instruments were recently calibrated and
adjusted, I would expect much better.

The report on the 3457A, dated 16 Feb says the 30 VDC range read
29.9991 VDC. The report on the VS330, dated 31 Mar says 10 VDC read
10.0001 VDC. Both instruments required adjustment.

These numbers would lead me to believe that I should be getting a lot
closer agreement to 10 VDC for both of these instruments. Am I
expecting too much?

Joe Gray
W5JG