Use of electrical measuring instruments and precautions - Solutions - Huaqiang Electronic Network

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Commonly used measuring instruments for electricians include shakers, multimeters, and clamp-type ammeters. These instruments do not pay attention to proper use or slight negligence during measurement. They do not burn the watch, or damage the device under test, and even endanger personal safety. Therefore, it is very important to master the correct use of common electrical measuring instruments.

1 Shake table is also called megohmmeter. Its purpose is to test the insulation condition of lines or electrical equipment. The methods of use and precautions are as follows:

(1) First select the shaker that matches the voltage level of the component under test. For lines or electrical equipment of 500V and below, use a 500V or 1000V shaker. 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, it should be carried out by two people.

(3) The power supply of the circuit under test or the electrical equipment must be completely disconnected before the measurement, that is, the insulation resistance is not allowed to be measured. And to find out that no work on the line or electrical equipment can be carried out.

(4) The surface used for the shake table must be insulated wire, and it is not suitable to use double stranded insulated wire. The end of the wire should have an insulating sheath; the line terminal “L” of the shake table should be connected to the tested device. Phase, grounding terminal "E" should be connected to the equipment casing and the non-measured phase of the equipment. The shielding terminal "G" should be connected to the protection ring or cable insulation sheath to reduce the error caused by the leakage current of the insulation surface.

(5) Open the road test before the measurement. When the "L" end and the "E" end of the shake table are idling, shake the table, and the pointer should point to "∞"; when the "L" end and the "E" end of the shake table are short-circuited, the pointer should be pointed to "0". ". The shaker function is good and can be used.

(6) The test line or electrical equipment must be grounded before testing. When testing the line, you must obtain permission from the other party.

(7) When measuring, the speed of shaking the handle of the table should be evenly 120r/min; after maintaining the stable speed for 1min, take the reading to avoid the influence of the absorption current.

(8) The two hands must not touch two wires at the same time during the test.

(9) After the test is completed, the thread should be removed first, and then the shaking table should be stopped. In order to prevent the electrical equipment from being reversely charged to the shaker, the shaker is damaged.

(10) When lightning is applied, it is strictly forbidden to test the line insulation.

2 Multimeter The multimeter is a comprehensive meter that measures the voltage and current of AC or DC. It can also measure the resistance of the component as well as the general parameters of the transistor and the gain of the amplifier. Therefore, the wiring of the multimeter changeover switch is complicated, and it is necessary to master the method of use.

(1) Before using the multimeter, calibrate the mechanical zero and electrical zero. To measure the current or voltage, first adjust the mechanical zero of the pointer; if you want to measure the resistance, you should first adjust the electrical zero of the pointer. In case the battery voltage in the watch drops, measurement error occurs.

(2) Before selecting the measurement, you must select the gear position, that is, the voltage, current or resistance, and also select the range. The primary election should be from big to small, so as not to break the pointer. It is forbidden to switch the range with power. The selection principle of the range is "U, I is in the upper part and R is in the middle", that is, when the voltage and current are measured, the pointer is above 1/2 of the dial, and when the resistance is measured, the pointer is in the middle of the dial. accurate.

(3) Pay attention to the polarity of the test leads when measuring DC. When measuring high voltage, insert the red and black test leads into the “2500V” and “-” jacks, place the multimeter on the insulation bracket, and then use the insulation tool to touch the test leads to the conductor under test.

(4) R×1 and R×10k range files must not be used when measuring transistors or integrated components.

(5) During the live measurement, care should be taken to prevent short circuits and electric shocks.

(6) When not in use, do not stop the switch in the ohms position to prevent the battery from being discharged when the test leads are shorted.

3 Clamp-on ammeter clamp-type ammeter is divided into high and low voltage, which is used to directly measure the current in the line without breaking the line. Its use is as follows:

(1) When using a high voltage clamp meter, pay attention to the voltage level of the clamp ammeter. It is strictly forbidden to measure the current of the high voltage circuit with a low voltage clamp meter. When measuring with a high-pressure clamp meter, it should be operated by two people. The non-on-duty personnel should also fill in the second work ticket. Wear insulated gloves when standing, and stand on the insulation mat. Do not touch other equipment to prevent short circuit or grounding.

(2) Observe the timing of the watch. Pay special attention to keep the safety distance between the head and the live part. The distance between any part of the human body and the charged body shall not be less than the entire length of the clamp meter.

(3) When measuring on a high voltage circuit, it is forbidden to use a wire to measure from the clamp ammeter. When measuring the current of each phase of the high-voltage cable, the distance between the cable head lines should be above 300mm, and the insulation is good. It can be considered when the measurement is convenient.

(4) When measuring the low-voltage fuse fuse or horizontally arranging the low-voltage bus current, the fuse fuses or busbars of each phase should be protected and insulated by the insulating material before the measurement to avoid phase-to-phase short circuit.

(5) When the cable has a phase connection, measurement is strictly prohibited. Preventing the breakdown of the ground due to the low insulation level of the cable head and endangering personal safety.

(6) Pull the switch to the maximum range after the measurement of the clamp ammeter to avoid accidental overcurrent during the next use; and keep it in a dry room.