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
I misread you were after 0.1 percent accuracy, dirty monitor. For 1 percent a 0.1 percent band gap reference would be fine You really have to go one order of precision better than what you are after.
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.
"Bert" wrote in news: snipped-for-privacy@vasbyt.isdsl.net:
bandgap reference diodes. They come in several voltages,much more accurate than the typical 3.5digit DMM. You can string several in series to obtain the voltages you want.
OR,you could buy an old Fluke differential voltmeter;they are precision voltage sources.
-- Jim Yanik jyanik at kua.net
If they are cheap, are you sure they can easily be calibrated?
Can you borrow a calibrated meter?
A fresh silver oxide cell is going to be very close to 1.55 volts and can be used as an initial check.
If they are cheap, are you sure they can easily be calibrated?
Can you borrow a calibrated meter?
A fresh silver oxide cell is going to be very close to 1.55 volts and can be used as an initial check.
Both can be calibrated and have presets inside, they are close with the help of some new batteries but not good enough. I do not know anyone with a callibrated meter. Thanks both of you.
Is that the most readily available cell for this purpose? Years ago I was told it was a zinc carbon - but *then* there might not have been many alternatives.
--
*You can't teach an old mouse new clicks *
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
Finding the keyboard operational Bert entered:
Well if you have enough meters to make it worth your while, something like Digikey part number MAX6012AEUR-TCT-ND would do it. True it's not near full scale but better then a battery. Bob
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-- Coffee worth staying up for - NY Times
Finding the keyboard operational Bert entered:
Well if you have enough meters to make it worth your while, something like Digikey part number MAX6012AEUR-TCT-ND would do it. True it's not near full scale but better then a battery. Bob
--
-- Coffee worth staying up for - NY Times
Did download a few datasheets of MAX Reference voltage IC's Will see what is available locally. Thank you very much Bert.
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