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UNI-T UT61E Multimeter teardown photos.

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tmammela:
Is it possible to calibrate resistance or current measurement in this meter? There seems to be many pots inside it but I've only seen discussion about dcv calibration. I have a dmmcheck plus incoming so I would have all needed references.

george graves:
WOuld like to know as well.

Benik3:

--- Quote from: Lightages on November 01, 2013, 04:57:55 am ---This is why everyone needs to put their country in their profile, or say what country they are from before asking anything.

--- End quote ---

I thought that I choose it in registration, but now I see that I don't have the flag on my profile.
Never mind, repaired :)

ModemHead:

--- Quote from: tmammela on November 01, 2013, 09:47:32 am ---Is it possible to calibrate resistance or current measurement in this meter? There seems to be many pots inside it but I've only seen discussion about dcv calibration. I have a dmmcheck plus incoming so I would have all needed references.

--- End quote ---
In my experience, it's not common to see calibration adjustments for resistance or current on manually-calibrated (trim-pot) handhelds.  Closed-case calibration units can of course calibrate any function/range using stored offsets.

A dual-slope integrating A/D converter is by its nature ratio-metric. Measuring resistance is done by passing a current through a reference resistor and the unknown resistance. The ADC measures the ratio of the voltages across the two resistors by switching it's reference input to the voltage across the known resistance.  The ratio of the voltages is also the ratio of the resistances, since the current is the same.

This means the accuracy of the resistance range is based mostly on the tolerance and tempco of the resistors used as the 'known'.  These are often dual-purposed from the voltage divider.  How close the multimeter comes to a known resistance measurement is a good indication of the quality of the parts in the front end, but not of the DCV calibration.  The DCV calibration is usually done by tweaking the voltage reference, and that isn't even used during resistance measurement.

For current ranges, it's measuring the voltage across the shunts, so both the DCV calibration and the tolerance and tempco of the shunts come into play.  Calibrating just the current without affecting voltage would require tweaking the shunts.

tmammela:

--- Quote from: ModemHead on November 01, 2013, 01:27:22 pm ---For current ranges, it's measuring the voltage across the shunts, so both the DCV calibration and the tolerance and tempco of the shunts come into play.  Calibrating just the current without affecting voltage would require tweaking the shunts.

--- End quote ---

Thank you. So no resistance calibration, that's fine. So ideally if I calibrate dcv it also calibrates current?

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