How to use a voltmeter What is the principle of a voltmeter?

How to use a voltmeter What is the principle of a voltmeter

The principle of a voltmeter p>

Voltmeter refers to the instrument fixedly installed on the panel of electric power, telecommunication and electronic equipment to measure the voltage in AC and DC circuits. 1) Commonly used voltmeters – voltmeter symbol: -V- 2) Most voltmeters are divided into two ranges. (0—3V) (0—15V) 3) Correct use: mechanical zero adjustment (adjust the pointer to zero scale) in parallel (the internal resistance of the voltmeter is very large, and a series connection in the circuit will cause an open circuit.) Positive input and negative output (making The current flows in from the positive connection and flows out from the negative connection.) Range (the voltage to be measured cannot exceed the range of the voltmeter, note: if the voltage on the circuit cannot be estimated, first use a large range to test the touch, and then roughly measure the voltage. , and then use a suitable range. This can prevent the pointer from being bent due to excessive voltage.) 4) The symbol of the DC voltmeter should add a _ under V, and the symbol of the AC voltmeter should add a wavy line “~” under V The voltmeter has three terminals, one negative terminal, and two positive terminals. For example, a voltmeter for students generally has two positive terminals, 3V and 15V. When measuring, select the range of “15V” according to the voltage. Each large grid represents 5V, and each small grid represents 0.5V (that is, the minimum division value is 0.5V); when the range is “3V”, each large grid on the dial represents lV, and each small grid represents 0. LV (ie, the minimum division value is 0.1V). We can use an ammeter to measure the magnitude of the current. The symbol of the ammeter is (A). The AC voltmeter is not divided into positive and negative poles. Select the correct range and directly connect the voltmeter in parallel with both ends of the circuit under test. The voltage measured by the AC voltmeter is the effective value of the AC voltage. Voltage characteristics of series and parallel circuits In a series circuit, the total voltage (the voltage across the power supply) is equal to the sum of the voltages across the resistors. U=U1+U2 In a parallel circuit, the voltages at both ends of each branch are equal and equal to the total voltage of the circuit (the voltage across the power supply). U=U1=U2

What is the principle of the voltmeter

In the voltmeter, there is a magnet and a wire coil. Make the coil generate a magnetic field, so that the coil will rotate under the action of the magnet after it is energized, which is the head part of the ammeter and the voltmeter. The current that this meter can pass is very small, and the voltage that it can withstand at both ends is also very small (definitely much less than 1V, maybe only a few tenths of a volt or even less). In order to measure the voltage in our actual circuit, we It is necessary to connect a relatively large resistor in series with this voltmeter to make a voltmeter. In this way, even if a relatively large voltage is applied to both ends, most of the voltage acts on the large resistor we added, and the voltage on the meter head will be very small. It can be seen that the voltmeter is an instrument with a large internal resistance, which should generally be greater than several thousand ohms. Classification of electronic voltmeters According to their working principles and reading methods, voltmeters are divided into two categories: analog voltmeters and digital voltmeters. (1) Analog voltmeter The analog voltmeter is also called the pointer voltmeter. Generally, the magnetoelectric DC current meter is used as the indicator of the measured voltage. When measuring DC voltage, it can be directly or amplified or attenuated into a certain amount of DC current to drive the pointer deflection indication of the DC meter. When measuring the AC voltage, it is necessary to pass the AC-DC converter, that is, the detector, to convert the AC voltage to be measured into a DC voltage proportional to it, and then measure the DC voltage. Analog voltmeters are divided into the following types according to different methods: ① Classification by operating frequency: divided into ultra-low frequency (below 1kHz), low frequency (below 1MHz), video (below 30MHz), high frequency or radio frequency (below 300MHz) ), UHF (above 300MHz) voltmeter. ②Classified by measuring voltage level: divided into voltmeter (basic range is V level) and millivolt meter (basic range is mV level). ③ Classification by detection method: divided into mean voltmeter, RMS voltmeter and peak voltmeter. ④Classified by circuit composition: divided into detection-amplification voltmeter, amplification-detection voltmeter, heterodyne voltage