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

Joseph Gray jgray at zianet.com
Fri Feb 12 23:45:43 EST 2016

The consensus seems to be that I was expecting more than I should
have. That's what I get for reading service manuals :-)

Other than the confusion over what I was expecting, I can't fault the
cal lab I sent the meter to. They are charging me a hobbyist-friendly
price and aren't going to charge me for the extra time involved to
re-enter the cal data (I offered to pay). If I were using this for
business, I would probably have used HP/Agilent/Keysight/whatever
they'll be called next month.

When I think about it, I really don't know if the DMM had cal
constants in it when I bought it second hand. I say this because the
battery had previously been replaced. I thought it was original, but
when I pulled the board, I could see obvious signs of hand soldering.
I had asked the previous owner if the battery had been replaced and he
said no. I guess I was lied to. Who knows if the person who replaced
the battery before did things properly, so as to save the cal data.
When I replaced the battery, I purposely didn't bother saving

Once I get the 3457A back, I'll check my EDC VS330 voltage standard. I
suspect that it is also out of spec. I realize that I should use a
3458A for this, as the specs on the VS330 and the 3457A are similar.
The good news is that the cal lab said that they could probably adjust
the VS330 if needed. I emailed them the manual and asked. They said
they offer a one hour free eval, so if they decide they can't do it,
I'd only be out shipping, if I send it to them.

David Kirby - Yes, I do remember your talking about removing the
battery in your DMM. As for doing it yourself (at least with the
3457A), yes, if you had the proper standards that were also
calibrated. As I recall from reading the service manual weeks ago, the
procedure is just hooking up the appropriate standard for each
function and range, then pushing buttons on the front panel. I don't
have the necessary equipment, so I sent it off.

I agree that it would make more sense to have fitted a second battery,
or at least some pins on the board where you could easily clip in a
temporary battery. Otherwise, you have to solder something in
temporarily. Thankfully, modern equipment uses non-volatile memory
that doesn't need a battery.

Thanks to all for the feedback.

Joe Gray

On Fri, Feb 12, 2016 at 4:24 PM, Dr. David Kirkby (Kirkby Microwave
Ltd) <drkirkby at kirkbymicrowave.co.uk> wrote:
> On 12 Feb 2016 21:12, "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.
> You may have seen my recent post on the 3457A. I was tempted to do as you
> done, on the assumption that Keysight would adjust the meter to give the
> best possible accuracy rather than just leave something untouched if it was
> within spec.  Someone warned me that if it caused errors at startup,  it
> might be considered needing a repair rather than just calibration.
> Did the meter indicate in any way that the cal constants were lost? A POST
> error or similar?
>> 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.
> So does that mean it is something one could do oneself without accurate
> standards?
>> 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.
> Ouch.
> I assume this means that your meter is probably calibrated more accurately
> than it would have been had any settings left unchanged if they were in
> spec.
> I have just bought a battery and intend fitting it soon.  I might ask
> Keysight about the constants.
> I really can't understand why they don't put two battery holders and a
> couple of diodes so a good battery in an one would be ok. Having to mess
> around desoldering batteries and hooking up power supplies seems crazy to
> me.
> Dr David Kirkby
> Managing Director
> Kirkby Microwave Ltd
> Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3
> 6DT, United Kingdom
> Registered in England and Wales as company number 08914892
> http://www.kirkbymicrowave.co.uk/
> Tel 07910 441670 / +44 7910 441670 (0900-2100 GMT)
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