The major difference between DC voltmeter and AC voltmeter is that the DC voltmeter measures the peak value of DC voltage while AC voltmeter measures the RMS value of AC voltage. Another significant factor which differentiates DC voltmeter and AC voltmeter is their working principle. The DC voltmeter selects a particular voltage and attenuates the rest of the range of voltage and then amplifies the selected voltage and passes it to PMMC meter.
AC voltmeter uses a rectifier before amplifying the signal so that the AC signal can be converted into DC and then this DC is passed to the moving coil magnet meter to vary the indication of the pointer and thereby measuring the RMS value of AC voltage.
Content: DC Voltmeter and AC Voltmeter
| Parameters | DC Voltmeter | AC Voltmeter |
|---|---|---|
| Full Form | Direct Current Voltmeter | Alternating Current Voltmeter |
| Definition | DC Voltmeter measures the peak value of DC voltage. | AC Voltmeter measures the rms value of AC voltage. |
| Construction architecture | The DC voltmeter consists of attenuator, followed by a multistage amplifier and a PMMC meter. | The AC voltmeter consists of attenuator, followed by a rectifier, a multistage amplifier and a PMMC meter. |
| Requirement of Rectifier | Not required | Required |
| Sensitivity | Highly sensitive | The AC voltmeters possess non-linear characteristics; due to this the measurements obtained at lower voltages are not accurate. |
Definition
DC Voltmeter
DC Voltmeter comprises an attenuator, multistage DC amplifier and a permanent magnet moving coil meter. The DC voltmeter measures peak value of DC Voltage applied to it.
The working procedure of DC voltmeter starts with an attenuator. The DC voltage which is to be measured is applied to the attenuator. The use of attenuator is to select the voltage range. Either transistor or field effect transistor (FET) is used for designing of the multi-stage amplifier.
There are two types of DC Voltmeter according to their construction; one is direct coupled Amplifier DC Voltmeter and Chopper type DC Voltmeter.
In the direct coupled amplifier, the transistors are cascaded in order to have higher gain from the amplifier. The cascading of the amplifier is done in such a way that the transistors are directly coupled with each other. Thus, in the process of direct coupling, the components required are less which makes the circuit simple and therefore direct coupling is done to reduce complexity.
The FETs can also be used in place of the transistor. The advantage of using FETs is that it possesses high input impedance. The high input impedance prevents the circuit from affecting the load terminal. In case of high current, the FET prevents the excess current to flow from measuring meter so that it does not burn out.
Chopper Type DC voltmeter uses a chopper modulator to convert the DC voltage into AC voltage and then pass it through AC amplifier. Then amplified AC signal is then again passed through Chopper demodulator and then through a low pass filter, it gets introduced in a PMMC meter for measuring peak value of DC voltage.
The Chopper type DC voltmeter provides high sensitivity as compared to direct coupled DC voltmeter.
AC Voltmeter
The AC voltage to be voltmeter comprises an attenuator, rectifier, multistage amplifier and a PMMC meter. The voltage measured is given as input to the AC voltmeter circuit. The AC voltage is converted into DC voltage with the help of rectifier.
The DC voltage obtained from the rectifier is passed through the multistage amplifier. The amplified signal obtained from the multistage amplifier is then passed to PMMC meter. The PMMC meter then moves the pointer according to the value of the RMS value of AC.
The AC voltmeters are of various types depending on the type of voltage is measures. The AC voltmeter which measures the average value of AC is called average reading AC voltmeter, the AC voltmeter which measures the peak value of AC is called peak reading AC voltmeters and the voltmeter which measures true RMS value is called True RMS reading Voltmeter.
Key Differences Between DC Voltmeter and AC Voltmeter
- The measuring quantity is the crucial factor which differentiates DC Voltmeter and AC Voltmeter. The DC voltmeter measures the DC voltage while AC voltmeter measures the AC voltage.
- Another key difference between DC voltmeter and AC voltmeter is that a DC voltmeter does not use rectifier before multistage amplifier while AC voltmeter uses rectifier before the multistage amplifier.
- The DC voltmeter measures the peak value of DC voltage while AC voltmeter measures the RMS value of the AC voltage.
Conclusion
The DC voltmeter and AC voltmeter both are the significant part of electronics instrumentation. The deciding factor for whether to use DC Voltmeter or AC voltmeter is the specific application on which we are working. If we are dealing with AC circuits, then with the help of AC ammeter we can measure RMS value of AC at any point of the circuit, but if we are dealing with DC circuit then DC voltmeter should be used.
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