Calibration Mode / Service Mode for AVO (Gossen-Metrawatt) M 2037

[CuriousCorn]

Hi all,

Welcome to my first post on this forum, for so long a useful source of information, but it's time for me to post a question.

I have inherited an AVO M 2037 folding multimeter (actually manufactured by Gossen Metrawatt, but rebadged as AVO, BBC, etc). After servicing it (battery corrosion, LCD problems - nothing a clean with IPA didn't solve), it now is a reasonably happy multimeter. But now for calibration. I have found how to enter the calibration mode; in the hinge is a small knob that is attached to a trimmer inside the multimeter. Turning this all the way to the left switches the multimeter to Calibration mode (seems a complex way to do it, but anyway). From there, I can not figure out how the calibration process works. I'm not sure if it really does need calibration that desperately, but my inquisitive nature will not let me stop until I have figured it out!

Does anybody have experience with this multimeter? Or, a service manual that explains the process? I contacted Gossen-Metrawatt, and they kindly gave me the user manual only, which of course does not have any information on the calibration process (they said that they don't have any other documents). Google throws up nothing.

Thanks in advance
Chris

[Huluvu]

Hi Chris

I would not suggest starting with adjustments at the Meter
Especially if you don't have all the proper standards to adjust the cardinal points   
Highly recommend to start with a kind of performance check to determine if something is wrong or faulty

Brgds Arne

[MosherIV]

Hi

It is a common misconception that calibration means adjustment.

In fact, if you send measurement devices for calibration, they first check it measures correctly and to within the specified tolerances.
The instrument is ONLY adjusted if a range is out of specification.
A report for the instrument is provided for the instrument, it lists all the ranges tested and what the deviation from the specification was during the calibration.

[CuriousCorn]

Hi all,

To follow up a little, the reason I would like to know the specific process for this multimeter is that I have the option of using our calibration facilities at work to check, and if necessary, adjust (obviously at no cost, perhaps a beer or two). There is certainly no way I can do it otherwise and it would be futile to do so. However, in the meantime, I can certainly play around (in comparison to measurements made with my Fluke 179, the M 2037 is functionally absolutely fine on all ranges).

But, nonetheless, as I have found out, the meter contains fixed calibration factors from when it was manufactured (in 1991/2; it was since never calibrated and sat unused (with batteries in it) for the best part of twenty years - not with me, with someone else from whom I inherited it). Anyway, these factors can be reloaded in calibration mode, but doing so also deletes any previous calibration. The zero point is set by shorting the DC terminals together and setting that. Then, example here is the the DC voltage calibration, the meter checks that the calibration voltage that is applied to the terminals is within range. For the 300 mV range this calibration voltage is 290 mV. If you apply anything else, 280 mV or 300 mV, it will refuse to accept it. But once it is within range, it assumes that it is 290 mV and calculates and stores the new calibration factor. Which, if you want you can delete and revert to the fixed factory factors. The same philosophy applies to all other ranges, 2.9 Vdc 29 Vdc, 290 Vdc, 29 mA, 290 mA, and so on.

What led me to find this information? The service manual for the Metrawatt MA 5D and the assumption that calibration processes across similar models from a similar vintage may be similar, and in this case it was.

Thanks,
Chris