A mechanical indicating meter for measuring DC voltage and AC voltage. Divided into DC voltmeter and AC voltmeter.
DC type
Mainly adopt the measuring mechanism of the magnetoelectric system electric meter and the electrostatic system electric meter. The magnetoelectric voltmeter consists of a small-range magnetoelectric ammeter and a series resistor (also known as a voltage divider), and the lowest range is more than ten millivolts. In order to expand the range of the voltmeter, the resistance value of the voltage divider can be increased. For example, when a 50 microampere ammeter is used to form a 250 volt voltmeter, the total resistance of the voltage divider and the measuring mechanism should be 250/[50×10^(-6)]=5×10^6 ohms=5 trillion This is equivalent to the internal resistance of the voltmeter of 20 kiloohms/volt. In order to avoid too much access to the voltmeter to affect the original working state, the voltmeter is required to have a higher internal resistance. A voltage divider composed of several resistors is connected in series with a measuring mechanism to form a multi-range voltmeter. The lowest range of the electrostatic voltmeter is tens of volts, and the expansion of the range is achieved by changing the internal structure of the meter and the distance between the electrodes. In addition, the measuring mechanism of the electromagnetic meter can also be used to measure DC voltage in theory.
Communication type
It mainly adopts the measuring mechanism of rectifier type electric meter, electromagnetic type electric meter, electric type electric meter and electrostatic type electric meter. Except for electrostatic voltmeters, other voltmeters are formed by connecting a small range ammeter in series with a voltage divider. A voltage divider composed of several resistors can also be connected in series with the measuring mechanism to form a multi-range voltmeter. These series of AC voltmeters are difficult to make low range, the lowest range is between a few volts to tens of volts, and the highest range is about 1 to 2 kilovolts. The lowest range of an electrostatic voltmeter is about 30 volts, and the highest range can be very high. The high-voltage voltmeter used in the power system is composed of an electromagnetic voltmeter with a rated voltage range of 100 volts, combined with a voltage transformer with an appropriate voltage transformation ratio. Due to the limitation of the coil inductance of the measuring mechanism, the use frequency range of the electromagnetic system voltmeter and the electric system voltmeter is relatively narrow, and the upper limit frequency is lower than 1 to 2 kilohertz. The electric system is slightly better than the electromagnetic system. Electrostatic and thermoelectric voltmeters have a wide frequency range. The upper limit of the operating frequency of the rectifier voltmeter is about several kilohertz, but it should be noted that the reading of the rectifier voltmeter is correct only when the AC voltage is a sinusoidal waveform. Refer to the table for the range, frequency range, internal resistance and the highest accuracy level that can be achieved for each series of voltmeters.
Digital display type
The digital display voltmeter is an instrument that uses an analog/digital converter to convert the measured voltage value into a digital form and displays it in digital form. It is suitable for use in an ambient temperature of 0～50℃ and humidity below 85%. When the voltage is abnormal due to lightning or other reasons, please use a power line filter or a non-linear resistor or other interference absorption circuit externally.
Nov 11, 2022
