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Voltmeter An Instrument For Measuring Voltage
Sep 11, 2017

The voltmeter is a measure of the voltage of the instrument, commonly used voltmeter - voltmeter. Symbol: V, there is a permanent magnet in the inside of the galvanometer, in the galvanometer between the two terminals in series by a wire composed of the coil, the coil placed in the permanent magnet of the magnetic field, and through the transmission device and the table pointer The Most of the voltmeter is divided into two ranges. The voltage meter has three terminals, a negative terminal, two positive terminals, the positive pole of the voltmeter is connected with the positive pole of the circuit, and the negative pole is connected with the negative pole of the circuit. The voltmeter must be connected in parallel with the appliance under test. The voltmeter is a fairly large resistor, ideally considered to be open. Junior high school laboratory commonly used voltmeter range of 0 ~ 3V and 0 ~ 15V.

The voltmeter is an instrument that measures the voltage, and the common voltmeter - voltmeter symbol is "V". The conventional pointer voltmeter includes a sensitive galvanometer with a permanent magnet inside the potentiometer, a series of wires formed by wires between the two terminals of the galvanometer. The coil is placed in the magnetic field of the permanent magnet and Through the transmission device connected with the table pointer. Most of the voltmeter is divided into two ranges. The voltage meter has three terminals, a negative terminal, two positive terminals, the positive pole of the voltmeter is connected with the positive pole of the circuit, and the negative pole is connected with the negative pole of the circuit.

The traditional pointer voltmeter and ammeter are based on a principle that is the magnetic effect of the current. The greater the current, the greater the magnetic force generated, the voltmeter is the greater the swing on the watch, the voltmeter has a magnet and a wire coil, through the current, the coil will produce a magnetic field, coil power In the role of the magnet will be deflected, which is the ammeter, voltmeter head part.

As the voltmeter to be measured in parallel with the measured resistance, so if the direct current meter with a voltmeter, the current is too large, will burn the meter, then the need to voltage in the internal circuit in series a large resistance , So after the transformation, when the voltmeter and then in parallel in the circuit, due to the role of resistance, the voltage applied to both ends of the meter most of the voltage is shared by the series resistance, so the current through the meter is actually very small, so Can be used normally. DC voltmeter symbols to V under a "_", AC voltmeter symbols to V plus a wave line "~".

Current meter and voltmeter use maintenance method

1. Reasonable choice of ammeter

(1) according to the accuracy of measurement requirements, a reasonable choice of ammeter accuracy. In general, the 0.1-0.2 grade magnetoelectric ammeter is suitable for use in standard and precise measurement; 0.5-1.5 magnetoelectric ammeter is suitable for use in laboratory measurement; 1.0-5.0 magnetoelectric instrument suitable for use In the industrial and mining enterprises as electrical equipment operation monitoring and electrical equipment maintenance use.

(2) according to the side of the current size of the corresponding limit of the ammeter. The amount of over the General Assembly caused by the measurement accuracy decreased, the limit is too small will cause damage to the ammeter. In order to make full use of the accuracy of the instrument, should be as far as possible the use of the standard scale after the principle of 1/4 select the instrument range.

(3) a reasonable choice of ammeter internal resistance. On the ammeter requirements of its internal resistance as little as possible o

2. Check before the measurement

Before measuring, check that the ammeter pointer is aligned with the "0" tick mark. If it is not aligned, adjust the "zero" to zero the pointer.

3. Ammeter and the circuit under test

(1) measurement, the ammeter should be connected to the low side of the circuit under test.

(2) When measuring DC, it is necessary to pay attention to the sign of the ammeter end button. For the single-limit ammeter, the measured current should flow out of the ammeter marked with "-" from the end tag "+" If the other end buttons are marked with a "+" symbol, the measured current should flow from the "+" end button and the "*" end button will flow out; if the other The end button is marked with a "-" sign, and the connection is just the opposite of the above.

4. Correct reading

When reading, make sure the pointer is stable and then read, and keep the line of sight perpendicular to the dial. If the dial has a mirror, the pointer and the pointer should be blended in the mirror to reduce the error.

5. Maintenance method

(1) As the magnetoelectric ammeter overload capacity is very small, the use of the circuit must pay attention to the polarity and limit of choice.

(2) If the pointer is found in the reverse deflection or forward deflection over the scale full scale line, should immediately stop the measurement, to be connected correctly or re-select a greater limit of the ammeter and then measured.

(3) When the measurement work is completed, you should first turn off the power, and then remove the ammeter from the measuring circuit, place it in a dry, ventilated and cool environment. On the sensitivity, high accuracy of the micro-ammeter and milliampere table, the application of the wire will be positive and negative button to connect to protect the instrument measuring mechanism.

The use of voltmeter maintenance methods and the use of ammeter maintenance methods, should also note the following:

(1) The voltmeter should be connected in parallel to the circuit under test.

(2) Since the voltmeter is parallel to the load, the internal resistance Rv is much larger than the load resistance RL.

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

(4) on the multi-limit voltmeter, when the need to change the amount of limit, the voltmeter should be broken off with the circuit under test, and then change the limit.