First post :) Having recently repaired a nonworking $5 hamfest special HP 34702A/34740A (4-1/2 digit DVM/display unit), I am interested in calibrating it. Without paying many times my purchase price to a lab! I obtained some sample MAX6325EPA (2.500V +/- 0.02%) which gets me "pretty close" for the 10V range. I also have a handy 596.5 ohm, 0.01% resistor for the Ohms ranges. The basic DC accuracy spec for the HP is something like +/- 0.03% plus 0.01% of range, so I need a better standard than that. Also I don't have a good way of generating very stable 10 KHz AC signals to cal those ranges... Much of the discussion on this list is 7.5 or 8.5 digit meters, so a 4.5 should be easy for you "Nuts". Any tips? thanks -Charles

Charles, Just a suggestion. If you post where you are located, perhaps a list member with better capability might announce himself and offer to help. Also, depending upon where you are located, less expensive alternatives might be available in the form of local calibration facilities. Failing all that, and depending upon your actual needs, perhaps obtaining a used Fluke 515 (inexpensive calibrator) would serve you better ? Then a one time expense for calibration of the 515 would serve for all your instrument needs. Of course, if you are not careful, you can sucked into the game and spend a lot of money on other more expensive calibration equipment to put you mind at ease. After all, Timenuts and Voltnuts are obsessive people. Bill....WB6BNQ (Located in San Diego) Charles wrote: > First post :) > > Having recently repaired a nonworking $5 hamfest special HP > 34702A/34740A (4-1/2 digit DVM/display unit), I am interested in > calibrating it. Without paying many times my purchase price to a > lab! > > I obtained some sample MAX6325EPA (2.500V +/- 0.02%) which gets me > "pretty close" for the 10V range. I also have a handy 596.5 ohm, > 0.01% resistor for the Ohms ranges. > > The basic DC accuracy spec for the HP is something like +/- 0.03% > plus 0.01% of range, so I need a better standard than that. Also I > don't have a good way of generating very stable 10 KHz AC signals > to cal those ranges... > > Much of the discussion on this list is 7.5 or 8.5 digit meters, so > a 4.5 should be easy for you "Nuts". Any tips? > thanks > -Charles > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

If you don't have access to formal calibration equipment, then what can be done is a best approximation by calibrating your DUT against a known calibrated DMM. You'll need voltage sources down to resolution of the DUT, and resistances for each range, and you'll use these to transfer the calibration of the DMM to the DUT; even non-metrological sources may be stable enough to transfer measurements made from seconds to minutes of measurement from the calibrated meter, to the DUT. Your DUT will not be calibrated to spec, but incudes the errors of the calibrated meter, and the error of your transfer references. For each range, use the voltage, current or resistances in the DUT's calibration manual, but make adjustments to match the calibrated DMM reading. For a final check you can compare both meters reading random voltage within every range, sampling untested resistors and currents, all appropriate per range. Why do this? At least the repaired DMM will be in a known measurement confidence area compared to totally unknown territory. Even if you don't have variable voltages or resistances, at least you can get some ranges in order with whatever you have, assuming the DUT does not have ranges that are dependent on the status of a one or several other ranges that are not calibrated. The same rationale can be used to get the AC ranges in order. In the absence of formal calibration equipment, its better than leaving it as is. At 01:37 PM 2/23/2011, Charles wrote: >First post :) > >Having recently repaired a nonworking $5 hamfest special HP >34702A/34740A (4-1/2 digit DVM/display unit), I am interested in >calibrating it. Without paying many times my purchase price to a >lab! > >I obtained some sample MAX6325EPA (2.500V +/- 0.02%) which gets me >"pretty close" for the 10V range. I also have a handy 596.5 ohm, >0.01% resistor for the Ohms ranges. > >The basic DC accuracy spec for the HP is something like +/- 0.03% >plus 0.01% of range, so I need a better standard than that. Also I >don't have a good way of generating very stable 10 KHz AC signals >to cal those ranges... > >Much of the discussion on this list is 7.5 or 8.5 digit meters, so >a 4.5 should be easy for you "Nuts". Any tips? >thanks >-Charles Sincerely, Marv Gozum Philadelphia, PA