Hello all I have a few digital multimeters which are in need of calibrating, cheap meters. How do I make a DC calibrating voltage source with say 1% accuracy, any voltage, prefer close to 1999 reading. Thank you very much Bert
Indirectly via a high precision resistor perhaps. I have some 8 Kohm ones to 0.01 per cent accuracy at manufacture anyway, presumably other sources of such resisrors
one of my tips from URL below
Callibrating a DVM and cross-calibrating a standard cell For anyone with access to a Weston cell but not access to a 5 or 6 digit DVM. I think this is how I cross-calibrated. I've dug out the docs and mine was calibrated at manufacture as
1.01866V at 20 deg C and -40 ppm/ deg C , 14 March 1979. estimate of uncertainty 10 ppm Perhaps 5 years ago I did the following with my cell and someone else's secondary standard cell. My DVM has a 300mV range for its 4 digits, or 200mV will do the same. With a NiCad in good condition in mid discharge and left for some hours to reach room temperature is a nominal 1.2V. What the actual voltage is does not matter as long as it is stable. Assume for convenience here 1.2V. Only use with DVMs ( high input impedence) . Then commoning negatives of Weston cell and NiCad, measured the difference so came in the 200mV range. Which brings it into the first 6 of 1.01866 then ratioing of the flashing digits gives an estimate for the fifth digit. So reading of 181.4 mV With DVM 2/3 time reading 181.4 and 1/3 time reading 181.3 so implying Weston Cell voltage of 1.01863 at 22 degrees C. The other cell / DVM test was about 1/3 to 2/3 the other way round on last digit agreeing with that cell's yearly calibration value. At the same time I checked a small standard cell salvaged from a bit of kit and it too was many years old but almost the same voltage, only last digit different again.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
Hello N Cook You brought me at an idea. Somewhere on the back of my shelf I have a very good mV meter, with the papers for working out the amount of mV at a certain temperature on all thermocouples, with a cold junction in between, normally in melting ice. Can not remember the make, but very expensive. This meter has a standard cell for reference, it also has a mV source coming out. Hope the standard cell is still working after 20 years and two new C cells in it. Thank you very much for the explaining. My head is becoming a bit rusted through age. Bert.