They are useful for testing power supplies for regulation. In fact, IMO, they are better for that than a DMM. Basically, you null the meter at light load, then apply a load and read the voltage (drop) out directly. It's trivial to see 1 mV on 100 V. YMMV, -John ====================== > Joe wrote: > >>The first one is a Fluke 893A and is solid state. >> * * * >>The second one is a Fluke 803B (I think. There is no label on it). >> * * * >>In the long run, are these things worth having? > > What they are good for is making DC measurements of very high > resistance sources without loading the source. They contain an > internal voltage reference, a voltage divider, and a null meter that > compares the divided reference to the unknown. Their accuracy > depends on the accuracy of the internal reference and the voltage > divider and the noise and offset of the null amp. [The 893A and 803B > also include both a normal TVM/VTVM mode and an AC rectifier, which > are nothing special.] > > Separate, high-accuracy components -- a precision woltage source such > as a Fluke 732A, a Kelvin-Varley bridge such as the Fluke 720A, and a > null meter such as the Keithley 155, Fluke 845A, or HP 419A -- can be > used in the null configuration to make voltage measurements about as > accurate as most home-lab amateurs can aspire to. > > In the 803B and 893A, the voltage reference and divider accuracy and > the null amp noise and offset are not as good as in the above > instruments, so both the accuracy and resolution of measurements are > correspondingly less. Typically, the last decade or two provide > resolution but not accuracy. > > These days, unless you are measuring DC sources with very high > resistance, a good DVM can do the same job more accurately and with > much less effort. But they are cool pieces of instrumentation > history, so if you are the curator type they may be worth having even > if you don't use them much or at all. > > Best regards, > > 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. > >