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How to use common electrical instruments?

Electrical instruments, such as shaker meters, multimeters, voltmeters, ammeters, resistance measuring instruments and clamp-type ammeters, etc. are often used. If these instruments do not pay attention to the correct use method or are slightly negligent during measurement, either the meter will be burned out, or It can damage the components under test and even endanger personal safety. Therefore, it is very important to master the correct use of common electrical instruments. Let’s learn with the editor of Xianji.com! ! !

1. How to use the shake table
The shaker, also known as the megohmmeter, is used to test the insulation condition of lines or electrical equipment. The usage and precautions are as follows:
1). First select a shaker that is compatible with the voltage level of the component under test. For circuits or electrical equipment of 500V and below, a 500V or 1000V shaker should be used. For lines or electrical equipment above 500V, a 1000V or 2500V shaker should be used.
2). When testing the insulation of high-voltage equipment with a shaker, two people should do it.
3). The power supply of the line under test or electrical equipment must be disconnected before measurement, that is, insulation resistance measurement with electricity is not allowed. And it can only be carried out after it is confirmed that no one is working on the line or electrical equipment.
4). The meter wire used by the shaker must be an insulated wire, and the twisted-stranded insulated wire should not be used. The end of the meter wire should have an insulating sheath; the line terminal “L” of the shaker should be connected to the measured phase of the equipment. , the ground terminal “E” should be connected to the equipment shell and the non-measured phase of the equipment, and the shielding terminal “G” should be connected to the protection ring or the cable insulation sheath to reduce the measurement error caused by the leakage current of the insulation surface.
5). Before the measurement, the open circuit calibration of the shaker should be carried out. When the “L” terminal and the “E” terminal of the shaker are unloaded, the pointer of the shaker should point to “∞”; when the “L” terminal of the shaker and the “E” terminal are short-circuited, the pointer of the shaker should point to “0″ “. Indicates that the shaker function is good and can be used.
6). The tested circuit or electrical equipment must be grounded and discharged before the test. When testing the line, you must obtain the permission of the other party before proceeding.
7). When measuring, the speed of shaking the handle of the shaker should be evenly 120r/min; after maintaining a stable speed for 1min, take the reading in order to avoid the influence of the absorbed current.
8). During the test, both hands should not touch the two wires at the same time.
9). After the test, the stitches should be removed first, and then stop shaking the watch. In order to prevent the reverse charging of the electrical equipment to the shaker and cause the shaker to be damaged.

2. How to use the multimeter
Multimeters can measure DC current, DC voltage, AC voltage, resistance, etc., and some can also measure power, inductance and capacitance, etc., and are one of the most commonly used instruments by electricians.
1). The selection of the terminal button (or jack) should be correct. The connecting wire of the red test lead should be connected to the red terminal button (or the jack marked “+”), and the connecting wire of the black test lead should be connected to the black terminal button (or the jack marked “-”). , Some multimeters are equipped with AC/DC 2500V measurement terminal buttons. When in use, the black test rod is still connected to the black terminal button (or the “-” jack), while the red test rod is connected to the 2500V terminal button (or in the socket).
2). The selection of the transfer switch position should be correct. Turn the switch to the desired position according to the measurement object. If the current is measured, the transfer switch should be turned to the corresponding current file, and the measured voltage should be turned to the corresponding voltage file. Some universal panels have two switches, one for the measurement type and the other for the measurement range. When using, you should first select the measurement type, and then select the measurement range.
3). The range selection should be appropriate. Depending on the approximate range being measured, turn the switch to the appropriate range for that type. When measuring voltage or current, it is best to keep the pointer in the range of one-half to two-thirds of the range, and the reading is more accurate.
4). Read correctly. There are many scales on the dial of the multimeter, which are suitable for different objects to be measured. Therefore, when measuring, when reading on the corresponding scale, attention should also be paid to the coordination of the scale reading and the range file to avoid errors.
5). Correct use of ohm gear.
First of all, select the appropriate magnification gear. When measuring resistance, the selection of the magnification gear should be so that the pointer stays in the thinner part of the scale line. The closer the pointer is to the middle of the scale, the more accurate the reading is. The tighter it is, the less accurate the reading will be.
Secondly, before measuring the resistance, you should touch the two test rods together, and turn the “zero adjustment knob” at the same time, so that the pointer just points to the zero position of the ohmic scale. This step is called ohmic zero adjustment. Every time you change the ohm gear, repeat this step before measuring the resistance to ensure the accuracy of the measurement. If the pointer cannot be adjusted to zero, the battery voltage is insufficient and needs to be replaced.
Finally, do not measure the resistance with electricity. When measuring resistance, the multimeter is powered by dry batteries. The resistance to be measured must not be charged, so as not to damage the meter head. When using the ohm gear gap, do not short the two test rods to avoid wasting the battery.

3. How to use the ammeter
The ammeter is connected in series in the circuit being measured to measure its current value. According to the nature of the measured current, it can be divided into DC ammeter, AC ammeter and AC-DC ammeter. The specific usage is as follows:
1). Be sure to connect the ammeter in series with the circuit under test.
2). When measuring DC current, the polarity of “+” and “-” of the terminal of the ammeter should not be wrongly connected, otherwise the meter may be damaged. Magnetoelectric ammeters are generally only used to measure DC current.
3). The appropriate range should be selected according to the measured current. For an ammeter with two ranges, it has three terminals. When using it, you should see the range mark of the terminal, and connect the common terminal and a range terminal in series in the circuit under test.
4). Select the appropriate accuracy to meet the needs of the measurand. The ammeter has internal resistance, the smaller the internal resistance, the closer the measured result is to the actual value. In order to improve the measurement accuracy, an ammeter with a smaller internal resistance should be used as much as possible.
5). When measuring the AC current with a large value, the current transformer is often used to expand the range of the AC ammeter. The rated current of the secondary coil of the current transformer is generally designed to be 5 amps, and the range of the AC ammeter used with it should also be 5 amps. The indicated value of the ammeter is multiplied by the transformation ratio of the current transformer, which is the value of the actual current measured. When using a current transformer, the secondary coil and iron core of the transformer should be grounded reliably. A fuse should not be installed at one end of the secondary coil, and it is strictly forbidden to open the circuit during use.

Fourth, the use of voltmeter
The voltmeter is connected in parallel with the circuit under test to measure the voltage value of the circuit under test. According to the nature of the measured voltage, it is divided into DC voltmeter, AC voltmeter and AC-DC dual-purpose voltmeter. The specific usage is as follows:
1). Be sure to connect the voltmeter in parallel with both ends of the circuit under test.
2). The range of the voltmeter should be greater than the voltage of the circuit under test to avoid damage to the voltmeter.
3). When using a magnetoelectric voltmeter to measure DC voltage, pay attention to the “+” and “-” polarity marks on the terminals of the voltmeter.
4). The voltmeter has internal resistance. The larger the internal resistance, the closer the measured result is to the actual value. In order to improve the accuracy of the measurement, a voltmeter with a larger internal resistance should be used as much as possible.
5). Use a voltage transformer when measuring high voltage. The primary coil of the voltage transformer is connected to the circuit under test in parallel, and the rated voltage of the secondary coil is 100 volts, which is connected to a voltmeter with a range of 100 volts. The indicated value of the voltmeter is multiplied by the transformation ratio of the voltage transformer, which is the value of the actual voltage measured. During the operation of the voltage transformer, the secondary coil should be strictly prevented from short-circuiting, and a fuse is usually set in the secondary coil as protection.

5. How to use the grounding resistance measuring instrument
The grounding resistance refers to the grounding body resistance and soil dissipation resistance buried in the ground. The method of use is as follows:
1). Disconnect the connection point between the grounding main line and the grounding body, or disconnect the connection points of all grounding branch lines on the grounding main line.
2). Insert two grounding rods into the ground 400mm deep, one is 40m away from the grounding body, and the other is 20m away from the grounding body.
3). Place the shaker in a flat place near the grounding body, and then connect it.
(1) Use a connecting wire to connect the wiring pile E on the table and the grounding body E’ of the grounding device.
(2) Use a connecting wire to connect the terminal C on the table and the grounding rod C’ 40m away from the grounding body.
(3) Use a connecting wire to connect the connecting post P on the table and the grounding rod P’ 20m away from the grounding body.
4). According to the grounding resistance requirements of the grounding body to be tested, adjust the coarse adjustment knob (there are three adjustable ranges on the top).
5). Shake the watch evenly at about 120 rpm. When the hand deflects, adjust the fine adjustment dial until the hand is centered. Multiply the reading set by the fine adjustment dial by the coarse adjustment positioning multiple, which is the grounding resistance of the grounding body to be measured. For example, the fine-tuning reading is 0.6, and the coarse-adjusting resistance positioning multiple is 10, then the measured grounding resistance is 6Ω.
6). In order to ensure the reliability of the measured grounding resistance value, the re-measurement should be performed again by changing the orientation. Take the average value of several measured values ​​as the grounding resistance of the grounding body.

6. How to use the clamp meter
A clamp meter is an instrument used to measure the magnitude of the current in a running electrical line, and it can measure the current without interruption. The clamp meter is essentially composed of a current transformer, a clamp wrench and a rectifier type magnetoelectric system reaction force meter. The specific usage methods are as follows:
1). Mechanical zero adjustment is required before measurement
2). Select the appropriate range, first select the large range, then select the small range or look at the nameplate value for estimation.
3). When the minimum measuring range is used, and the reading is not obvious, the wire under test can be wound a few turns, and the number of turns should be based on the number of turns in the center of the jaw, then the reading = indicated value × range/full deviation × number of turns
4). When measuring, the conductor under test should be in the center of the jaws, and the jaws should be closed tightly to reduce errors.
5). After the measurement is completed, the transfer switch should be placed at the most range.


Post time: Nov-21-2022