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The sensitivity and input resistance of a voltmeter can be increased if the current required to deflect the meter pointer is supplied by an amplifier and power supply instead of by the circuit under test. The electronic amplifier between input and meter gives two benefits; a rugged moving coil instrument can be used, since its sensitivity need ...
Solenoid voltmeters are useless on low-voltage circuits (for example, 12 volt circuits). The basic range of the voltmeter starts at around 90V (AC or DC). Solenoid voltmeters are not precise. For example, there would be no reliably perceptible difference in the reading between 220 VAC and 240 VAC. They are meant for intermittent operation.
An electrostatic voltmeter uses the attraction force between two charged surfaces to create a deflection of a pointer directly calibrated in volts. Since the attraction force is the same regardless of the polarity of the charged surfaces (as long as the charge is opposite), the electrostatic voltmeter can measure DC voltages of either polarity.
The following items are used for basic measurement of voltages, currents, and components in the circuit under test. Voltmeter (Measures voltage) Ohmmeter (Measures resistance) Ammeter, e.g. Galvanometer or Milliammeter (Measures current) Multimeter e.g., VOM (Volt-Ohm-Milliammeter) or DMM (Digital Multimeter) (Measures all of the above)
A modern electrometer is a highly sensitive electronic voltmeter whose input impedance is so high that the current flowing into it can be considered, for most practical purposes, to be zero. The actual value of input resistance for modern electronic electrometers is around 10 14 Ω, compared to around 10 10 Ω for nanovoltmeters. [9]
Ideally the measuring device should not affect the circuit parameters i.e., the internal impedance of the ammeter should be zero (no voltage drop over the ammeter) and the internal impedance of the voltmeter should be infinite (no current through the voltmeter). However, in actual case, ammeters have a low but non zero impedance and voltmeters ...
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