The Museum of T&M Instruments

"The Fluke Model 893A AC-DC Differential Voltmeters provide conventional or differential measurements of ac voltages from one millivolts to 1100 volts and dc voltages from 10 microvolts to 1100 volts. Conventional (TVM) measurements are made with an accuracy of ±3% of the selected range to initially determine the magnitude of the measured voltage. The differential (NULL) mode is then used with an improved accuracy of up to 250% over that of the conventional mode to determine the exact value of the measured voltage. One linear meter-scale greatly simplifies all measurements made with the instrument. Whenever the instrument is operated in the differential mode, an inline digital readout representing the magnitude of the measured voltage is available from the front panel readout dials." (Fluke, Manual 893A, 1971-1975)

BRIEF SPECS

Range	1V to 1000V f.s.
DCV Accuracy	up to 0.01%
Output	1V f.s.
Power	4 watts
Dimensions	9-3/4" x 7" x 13-3/8"
Weight	4 lbs
Technology	transistor, ic
Price	unknown

This is one of the last differential voltmeters manufactured by it's inventor J. Fluke Co. It is actually a digital meter where the D/A-converter (3 digits plus one pot) is controlled by operator's hand. Long time they were the only possibility to make extreme accurate measurements. But after introduction of the digital voltmeter Fluke's position began to dimish, until they launch their own dvm (model 8300). Today I like it to make adjustments by enter the setpoint voltage at the dials and adjust the device under test until the meter comes to zero.