Now look at the vacuum tube voltmeter, TS-375A U, on page 159. The vacuum tube voltmeter is one of the most useful single unit instruments. In this unit, the voltage to be measured is applied to the control grid of an electron tube. Measurements and calibration
Vacuum Tube Voltmeter TS-375A/U
are made in terms of the plate current of the tube. Thus, this meter draws less current from the circuit being measured than does an ordinary voltmeter. Therefore, measurements made with a vacuum tube voltmeter more nearly indicate actual circuit conditions, since the meter does not load the circuit being tested.
The vacuum tube voltmeter has other advantages also. It may operate at high frequencies, while the ordinary voltmeter is limited to frequencies below a few kc. The use of an electron tube also protects the meter from overloading, and makes it an almost foolproof voltmeter. However, because of the tube, the voltmeter must have a source of power for its operation. It may be operated from AC line voltage or from self-contained batteries.
Was this article helpful?