How Do I Use a Voltmeter?

A voltmeter is an instrument that measures voltage. It is composed of a permanent magnet, a coil, and the like. A voltmeter is a fairly large resistor, ideally considered an open circuit. The range of voltmeters commonly used in junior high school laboratories is 0 ~ 3V and 0 ~ 15V.

A voltmeter is an instrument for measuring voltage. Commonly used voltmeters

Traditional analog voltmeter and

This article briefly describes the use and maintenance methods of ammeters and voltmeters.

1. Reasonable choice of ammeter

(1) Accurately select the accuracy of the ammeter according to the accuracy requirements of the measured. Generally speaking, magnetoelectric ammeters of class 0.1-0.2 are suitable for standard meters and precision measurement; magnetoelectric ammeters of class 0.5-1.5 are suitable for measurement in the laboratory; magnetoelectric meters of class 1.0-5.0 are suitable for use Used in industrial and mining enterprises for electrical equipment operation monitoring and electrical equipment maintenance.

(2) Select the corresponding ammeter based on the magnitude of the current on the side. Excessive limit will cause the measurement accuracy to decrease, and too small limit will damage the ammeter. In order to make full use of the accuracy of the meter, the range of the meter should be selected according to the principle of using the last quarter of the standard scale as much as possible.

(3) Reasonably select the internal resistance of the ammeter. The smaller the internal resistance of the ammeter, the better.

2. Inspection before measurement

Before measurement, check whether the pointer of the ammeter is aligned with the "0" scale. If it is not aligned, adjust the "Zero Adjuster" to reset the pointer to zero.

3. Connection of ammeter and circuit under test

(1) When measuring, the ammeter should be connected in series to the low potential side of the circuit under test.

(2) When measuring DC, you need to pay attention to the symbol of the end button of the ammeter. For single-quantity limit ammeter, the measured current should flow from the end button marked with + into the ammeter, and flow out of the ammeter from the end button marked with Multi-limit current meter. The * mark is the common end button. If the other end buttons are marked with + symbol, the measured current should flow from the + end button and flow out from the * end button. The end button is marked with a "-" symbol, the connection is exactly the opposite of the above.

4. Correct reading

When taking the reading, the pointer should be stabilized before reading, and keep the line of sight perpendicular to the scale as soon as possible. If the dial has a mirror, the pointer and the shadow of the pointer in the mirror should be overlapped to reduce the error.

5. Maintenance method

(1) Because the overload capacity of the magneto-electric current meter is very small, pay attention to the selection of the polarity and quantity limit of the connection circuit when using it.

(2) If it is found that the pointer's reverse deflection or forward deflection exceeds the full scale line on the scale, the measurement should be stopped immediately after the power is turned off, and the measurement should be performed after the connection is correct or a larger amount of ammeter is selected.

(3) When the measurement is completed, the power should be turned off first, then the ammeter should be removed from the measurement circuit, and placed in a dry, ventilated and cool environment. For micro-ampere meters and milli-amp meters with high sensitivity and accuracy, wires are used to connect the positive and negative terminals to protect the measuring mechanism of the instrument.

The method of using and maintaining the voltmeter is similar to the method of using and maintaining the ammeter. The following points should also be noted:

(1) When measuring, connect the voltmeter in parallel to the circuit under test.

(2) Since the voltmeter and the load are connected in parallel, the internal resistance Rv is required to be far greater than the load resistance RL.

(3) When measuring DC, first connect the "-" Rui button of the voltmeter to the low potential terminal of the circuit under test, and then connect the "+" button to the high potential terminal of the circuit under test.

(4) For multi-quantity limit voltmeters, when the volume limit needs to be changed, the voltmeter should be disconnected from the circuit under test before changing the limit. ^[3]