[volt-nuts] Just back from cal

Tom Miller tmiller11147 at verizon.net
Fri Apr 8 00:43:42 EDT 2016

You really won't know what is going on until you do the next calibration 
cycle and examine the as received data for both units. Or find someone with 
a better meter or reference and compare them.

Who did the calibration?

You might leave both units powered up for a few days/weeks and see how they 
behave together. Also, you are two degrees C above you lab calibration 
temperature. That could add to the uncertainty.

----- Original Message ----- 
From: "Joseph Gray" <jgray at zianet.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Thursday, April 07, 2016 11:20 PM
Subject: [volt-nuts] Just back from cal

> 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
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