EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: eric.niu on December 02, 2019, 10:15:42 am
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Guys, I was playing my 18s yesterday and guess what, I accidentally found out how to calibrate this instrument. Here is the steps
1. Power off your DMM and open the case.
2. Turn the screw clockwise to the end, then power on, you will see MAN on the display, now it's in calibaration mode, not possible to switch to auto range
3. The calibration point is 0 and 285 digits, for example when you calibrate 300.00 mV range you need calibrate 0 and +- 285 mv. other ranges are similar. Adjust the input signal and press the DATA/MINMAX key, you will see CAL on the display, a short beep means your input is accepted.
4. When you done the calibation turn the screw back to the end, power off and power on you 18s, enjoy your calibated device now.
[attachimg=1]
Cheers
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Although I haven't been able to find photos of the 18s to confirm, I think it is based on a Maxim DMM ADC.
The "screw" is likely to be the trim for ADC Vref so, yes very important for calibration.
I don't see why this would be a way to set the DMM to a calibration mode though, at the best the CPU can detect that Vref is out of range and push user to do something about it.
I would be very surprised that this DMM has ability to store calibration data for each range separately, more likely once you have one range adjusted they should all be good?
I could be wrong of course...
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Thanks for the comments, in the beginning I also thought that VR is for Vref adjustment, I tried adjust it but the display changed nothing.