[time-nuts] Calibration procedures - what is normal?

[Daniel Watson]

Hi,

I had an interesting experience with a local cal lab when I took in my HP
5334B (Option 010). I'd recently purchased the unit and had no idea of its
calibration history. At the time I wasn't quite a time nut, and I didn't
own a reference to check frequency accuracy myself. I was hoping to get the
counter and its timebase calibrated to use as a reference at home. I
checked the service manual and got the impression that this was part of the
procedure. I also told the tech what I was looking for when I dropped it
off. Can you see where this is going?

A few days later I picked up the unit, and the cal certificate listed the
frequency accuracy as perfect to 9 digits with no adjustment needed. That
raised an eyebrow. When I got it home, I immediately noticed the reference
selector had been switched to external. Sure enough, no adjustment to the
OCXO had been made. They used their lab reference externally during the
procedure. I contacted them, they said they followed the listed procedure
for this counter, but nonetheless offered to help. I took the unit back and
they plugged it in for 10 minutes to let it "stabilize", then gave me the
count of their standard on one of the channels written on a sticky note...

Needless to say, that experience motivated me to get more serious about
this stuff and invest in some good references.

Dan


On Fri, Feb 12, 2016 at 3:14 PM, Joseph Gray <jgray at zianet.com> wrote:

> I sent my HP 3457A in for cal. I should be getting it back next week.
> I won't mention where I sent it, but it wasn't Keysight (I don't like
> that name). I recently changed the SRAM battery and purposely did not
> save the cal constants. I bought the meter second hand and it wasn't
> in spec when I bought it. I didn't care what the past data was.
>
> The service manual lists an entire sequence of procedures for
> calibrating this DMM, starting with storing values for zero and full
> scale into the SRAM. All of this is done via the front panel, by
> pushing buttons.
>
> I just found out that this part of the procedure is not normally done
> (at least by the lab I sent the DMM to). With no pre-existing cal
> constants, the tech I spoke to was rather annoyed that he was having
> to spend the time doing the hookups and pushing buttons for each
> function and range to store the zero and full scale values. I was told
> this added an extra hour to the normal procedure.
>
> Not knowing what is normally done in the cal lab, I assumed that the
> entire procedure as listed in the service manual would be done. It
> seems that I was wrong.
>
> In the end, the lab decided not to charge me for the extra time
> involved. I thanked them for that.
>
> My question is, do any cal labs (including Keysight) normally perform
> the zero and full scale procedures as listed in the service manual?
>
> Joe Gray
> W5JG
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