Fluke 335D

The 335D DC Voltage Standard provides functions of a precision direct voltage standard along with those of a differential voltmeter and a high impedance null detector. As a DC voltage standard, range is 1 ?V to 1000 V with an accuracy of 0.001%. Will deliver up to 50 mA of current. In differential voltmeter mode, the "infinite" input resistance of true potentiometric measurement is obtained by adjusting the output of the calibrator to equal the unknown voltage, as indicated by zero deflection of the null detector.

Fluke 335D datasheet & specifications