What Is an Electronic Voltmeter?

An electronic voltmeter is an instrument used to measure voltage. The measured voltage range is wide and the frequency range is wide. Its input impedance is large, and it will not change the working state of the circuit under test after being connected, so it can measure the real voltage. The reading has gradually changed from the pointer type to the LCD display. And it has programmed control and can shift gears automatically.

Electronic voltmeter (also known as

The measured voltage is first attenuated by the attenuator to a value suitable for the input of the AC amplifier, then amplified by the AC voltage amplifier, and finally detected by the detector to obtain a DC voltage, and the value of the value is indicated by the meter head.

The deflection angle of the pointer of the electronic voltmeter is proportional to the average value of the measured voltage, but the panel is scaled according to the effective value of the sinusoidal AC voltage. Therefore, the electronic voltmeter can only be used to measure the effective value of the sinusoidal AC voltage. When measuring non-sinusoidal AC voltage, the reading of the electronic voltmeter has no direct meaning. Only by dividing this reading by 1.11 (the waveform coefficient of the sinusoidal AC voltage) can the average value of the measured voltage be obtained. ^[2]

Compared with ordinary multimeters, electronic voltmeters have the following advantages:

(1) The input impedance is high. Typical input resistance is 500 k to 1 M. After the meter is connected to the circuit under test, the impact on the circuit is small.

(2) Wide frequency range. Suitable for 20 Hz 2 MHz (but cannot measure DC signal).

(3) High sensitivity. The lowest voltage can be measured in microvolts.

(4) Wide voltage measurement range. The measuring range of the meter can be from 100V to 300V. ^[1]

According to different working principles and reading methods, electronic voltmeters can be divided into two types: analog voltmeters and digital voltmeters.

1. Analog voltmeter

The analog voltmeter generally refers to the pointer voltmeter, which adds the measured voltage to the magnetoelectric current meter and converts it into the size of the pointer deflection angle to measure. When measuring DC voltage, it can directly or through amplification or attenuation become a certain amount of DC current to drive the pointer deflection indication of the DC meter head. When measuring AC voltage, the AC / DC converter or detector must be used to convert the measured AC voltage into a DC voltage proportional to it before measuring the DC voltage. According to different classification methods, there are many types of analog voltmeters.

(1) According to different operating frequencies, analog voltmeters can be divided into ultra-low frequency (below 1kHz) voltmeters, low-frequency (below 1MHz) voltmeters, video (below 30MHz) voltmeters, and high-frequency or radio frequency (below 300MHz) voltage Meter and UHF (above 300MHz) voltmeter.

(2) According to the magnitude of the measured voltage, the analog voltmeter can be divided into a voltmeter with a basic range of V magnitude and a millivolt meter with a basic range of mV magnitude.

(3) According to different detection methods, analog voltmeters can be divided into mean voltmeters, rms voltmeters and peak voltmeters.

(4) According to the composition of the circuit, the analog voltmeter can be divided into three types: detection-amplification voltmeter, amplification-detection voltmeter and heterodyne voltmeter.

2. Digital voltmeter

The digital voltmeter converts the value of the measured voltage into a digital quantity through digital technology, and then displays the measured voltage value as a decimal number. The digital voltmeter uses the A / D converter as the measurement mechanism, and displays the measurement results with a digital display. Digital voltmeters that measure AC voltage and other electrical parameters must convert the measured electrical parameters before the A / D converter to convert the measured electrical parameters into DC voltage.

Digital voltmeters can be divided into DC digital voltmeters and AC digital voltmeters according to the measurement objects. DC digital voltmeters can be divided into three types of comparison type, integral type and composite type according to the different A / D converter methods. According to the different AC / DC conversion principles, the AC digital voltmeter can be divided into three types: peak type, average value type and effective value type.

Digital voltmeter uses digital form to output and display the measurement results. In addition to high measurement accuracy, fast speed,

The performance indicators of the electronic voltmeter mainly include the following items.

(1) Operating frequency range. This range refers to the frequency range in which the electronic voltmeter measures with a specified accuracy. The size of this range is closely related to the circuit structure of the electronic voltmeter. Different types of voltmeters have different operating frequency ranges. Therefore, an appropriate electronic voltmeter must be selected according to the frequency range of the measured signal.

(2) Sensitivity and range. Range refers to the voltage range that the electronic voltmeter can measure; sensitivity refers to the lower limit of the range.

(3) Accuracy and working error. The accuracy of an electronic voltmeter is usually characterized by systematic errors such as basic errors, frequency-added errors, and temperature-added errors. The accuracy of different types of electronic voltmeters is different. Generally, the basic error of the electronic voltmeter is about ± 2%.

(4)

(1) Mechanical zero adjustment: Before turning on the power of the instrument, check whether the pointer is at zero. If it is not at zero, adjust the mechanical zeroing screw so that the pointer is at zero.

(2) Before use, the instrument should be powered on for 20 minutes to warm up. Do not power off when not in use to avoid affecting the stability.

(3) When the input terminal of the instrument is open-circuited, the external sensing signal may cause the pointer to deflect beyond the limit and damage the meter head. Therefore, after the measurement is completed, the two ends of the test wire should be shorted.

(4) Select the correct range: The appropriate range should be selected according to the measured voltage, so that the pointer of the meter is deflected to more than 1/3 of the full scale. If you do not know the approximate value of the measured voltage in advance, you should first set the range switch to Large range, and then gradually decrease the range.

(5) Correct reading: According to the position of the range switch, press the corresponding scale line. ^[1]