Vacuum Tube Voltmeter (VTVM)

Q. What is VTVM?

Answer. VTVM is a vacuum tube voltmeter. It makes the use of vacuum tube(s) as an active device.

Q. Enlist the types of VTVMs?

Answer. Average reading, peak reading, slide back, logarithmic, balanced Bridge and electrometer VTVMs are the different types of VTVM.

Q. Enlist TVMs.

Answer. 1. TVM with cascaded transistor.

2. TVM with FET (field effect transistor)

3. Balanced bridge TVM

4. Chopper amplifier

Q. Where is VTVM used?

Answer. VTVMs are used for the measurement of the dc and ac voltages.

Q. What is the difference between VTVM and TVM?

Answer. Electronic voltmeter using vacuum tube is called a VTVM while that using a transistor is called a TVM.

Q. In what respect a TVM is inferior to VTVM?

Answer. The only disadvantage with VTVM is its low input impedance which it offers in comparison to VTVM but this shortcoming is overcome by using FET in the input stage of the voltmeter.

Q. What are the advantages of TVM over VTVM?

Answer. The advantages of TVMs over VTVMs are given below

  1. TVM does not require any warm up time because of an absence of the heating element.
  2. Use of transistor makes the instrument portable because of its light weight.
  3. A transistorized instrument can be operated on low voltage i.e. on battery so TVM is well suited for the field work where power sources are not available.
  4. VTVM cannot measure current directly because of its high resistance whereas TVM can do.
  5. TVM consumes very less power because of an absence of the heating element.

Q. What is the difference between DC voltmeter and AC voltmeter?

Answer. Fundamentally DC and AC voltmeter are not much different DC voltmeter consists of a DC amplifier succeeded by a conventional DC meter while and ac voltmeter consists of an additional rectifier either before or after the amplifier

Q. Why is direct coupled amplifier DC voltmeter commonly used

Answer. Because of its low cost

Q. How can an average reading VTVM be converted to and RMS reading voltmeter?

Answer. The average reading voltmeter can be converted into and RMS reading voltmeter by calibrating its metre scale in terms of the RMS value of sinusoidal wave.

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