Following are the difference between volt ohm milliammeter (VOM) and vacuum tube voltmeter (VTVM) :
|Volt ohm milliammeter (VOM)
||Vacuum tube voltmeter (VTVM)
|In volt ohm milliammeter, DC voltmeter resistance changes with range.
||It is the same for all ranges measures ac volts.
|Volt ohm milliammeter is portable.
||Vacuum tube voltmeter is usually plugged into power line.
|Its ohm range is usually upto R x 10,000 Ω.
||Its ohm range is upto R x 1M Ω.
|Zero ohm adjustment has to be changed for each range.
||Zero ohm adjustment is the same for all ranges.
|It measure ac volts.
||It measures ac volts.
|It measures current directly.
||It cannot measure current directly because of its high resistance.