First, the use of the clamp meter
A clamp meter is a meter that measures the amount of current flowing on an electrical circuit that can measure current under uninterrupted power.
1. Structure and principle of the clamp meter
The clamp meter consists essentially of a current transformer, a clamp wrench and a rectifying magnetoelectric system with a reaction force meter.
2. How to use the clamp meter
(1) Mechanical zeroing before measurement
(2) Select the appropriate range, first select the large, then select the small range or look at the nameplate value estimate.
(3) When the minimum range measurement is used and the reading is not obvious, the measured wire 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 = indication value × range / full deviation × åŒnumber
(4) When measuring, the wire to be tested should be placed in the center of the jaws and the jaws should be closed tightly to reduce the error.
(5) After the measurement is completed, the transfer switch should be placed at the most range.
3. Precautions for the clamp meter
(1) The voltage of the line under test is lower than the rated voltage of the clamp meter.
(2) When measuring the current of the high-voltage line, wear insulated gloves, wear insulated shoes, and stand on the insulating mat.
(3) The jaws should be closed tightly and cannot be charged for the range.
Second, the use of megohmmeter
When the megohmmeter is working, it generates high voltage itself, and the measuring object is electrical equipment, so it must be used correctly, otherwise it will cause personal or equipment accidents. Before using, you must first make the following preparations:
1. The power of the equipment under test must be cut off before the quantity is measured, and the ground should be short-circuited and discharged. The equipment must not be energized for measurement to ensure the safety of the person and equipment.
2. For equipment that may induce high voltage, the possibility must be eliminated before measurement can be made.
3. The surface of the object to be tested should be cleaned to reduce the contact resistance and ensure the correctness of the measurement results.
4. Before the measurement, check whether the megohmmeter is in normal working condition, mainly check the two points of “0†and “∞â€. That is, the handle is shaken to make the motor reach the rated speed. The megger should be in the “0†position when it is short-circuited and “∞†when it is open.
5. The megger should be placed in a stable and stable place and away from large external current conductors and external magnetic fields.
After the above preparations are made, the measurement can be carried out. When measuring, pay attention to the correct wiring of the megohmmeter, otherwise it will cause unnecessary errors or even errors.
There are three terminals of the megohmmeter: one is “Lâ€, that is, the line end, one “E†is the ground end, and another “G†is the shield end (also called the protection ring). Generally, the insulation resistances to be tested are connected. Between the "L" and "E" ends, but when the surface of the insulator to be tested is seriously leaky, the shield ring of the test object or the portion not to be measured must be connected to the "G" end. Thus, the leakage current flows directly back to the negative end of the generator via the shield end "G" to form a loop, rather than flowing through the megohmmeter measuring mechanism (moving coil). This fundamentally eliminates the influence of surface leakage current. In particular, it should be noted that when measuring the insulation resistance between the cable core and the outer surface, the shield terminal "G" must be connected because the air humidity is high or the cable is insulated. When the surface is not clean, the leakage current on the surface will be very large. In order to prevent the measured object from being affected by leakage, its internal insulation measurement is generally added to the outer surface of the cable with a metal shielding ring, and the megger of the megohmmeter. "End connected.
When using the megohmmeter to measure the insulation resistance of electrical equipment, be sure to note that the "L" and "E" ends cannot be reversed. The correct connection is: "L" line end button is connected to the conductor of the device under test, "E" The grounding device is grounded, and the “G†shield terminates the insulated part of the device under test. If the "L" and "E" are reversed, the leakage current flowing through the insulator and the surface is collected to the ground through the outer casing, and the ground flows through the "L" into the measuring coil, so that the "G" loses the shielding effect and gives the measuring tape. There is a big error. In addition, because the inner lead of the "E" end is insulated from the outer casing by a degree of insulation lower than the "L" end and the outer casing, when the megohmmeter is placed on the ground, when the correct wiring is used, the "E" end is opposite to the outer casing of the instrument. The insulation resistance of the shell to the ground is equivalent to a short circuit and does not cause an error. When the "L" and the "E" are reversed, the insulation resistance of the "E" to the ground is in parallel with the measured insulation resistance, and the measurement result is biased. Small, causing large errors in the measurement.
Third, exchange millivoltmeter use precautions
1. Short-circuit and zero adjustment before measurement. Turn on the power switch, clamp the red and black clips of the test line (also called the open cable), turn the range knob to the 1mv range, and the pointer should be at the zero position (some millivoltmeters can pass the zero potentiometer on the panel) For zero adjustment, if the panel has no zero potentiometer, the internal zero potentiometer has been adjusted). If the pointer does not point to the zero position, check the test line for open circuit or poor contact. Replace the test line.
2. The sensitivity of the AC millivoltmeter is high. After the power is turned on, the pointer will deflect due to the interference signal (sensing signal) at a lower range, which is called self-starting phenomenon. Therefore, when the signal is not tested, the range knob should be turned to the higher range to prevent the pointer from being bent.
3. When the AC millivoltmeter is connected to the circuit under test, its ground (black clip) should always be connected to the ground of the circuit (become a common ground) to prevent interference.
4. When adjusting the signal, first turn the range knob to a larger range, then change the signal and then gradually reduce it.
5. AC millivoltmeter dial scale is divided into 0-1 and 0-3 scales, range knob switching range is divided into every range (1mv, 10mv, 0.1v...) and every three ranges (3mv, 30mv, 0.3) v......), where the range of the scale is directly read on the 0-1 scale line, where the range of the third is directly read on the 0-3 scale line, the unit is the unit of the range, no conversion is required.
6. Before use, check whether the range knob and the range mark are consistent. If the position is wrong, the reading will be wrong.
7. The AC millivoltmeter can only be used to measure the rms value of a sinusoidal AC signal. If a non-sinusoidal AC signal is measured, it is converted.
8. Note: The AC voltage of the multimeter cannot be used instead of the AC millivoltmeter to measure the AC voltage (the internal resistance of the multimeter is low, which is used to measure the power frequency voltage of 50Hz or so).
A clamp meter is a meter that measures the amount of current flowing on an electrical circuit that can measure current under uninterrupted power.
1. Structure and principle of the clamp meter
The clamp meter consists essentially of a current transformer, a clamp wrench and a rectifying magnetoelectric system with a reaction force meter.
2. How to use the clamp meter
(1) Mechanical zeroing before measurement
(2) Select the appropriate range, first select the large, then select the small range or look at the nameplate value estimate.
(3) When the minimum range measurement is used and the reading is not obvious, the measured wire 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 = indication value × range / full deviation × åŒnumber
(4) When measuring, the wire to be tested should be placed in the center of the jaws and the jaws should be closed tightly to reduce the error.
(5) After the measurement is completed, the transfer switch should be placed at the most range.
3. Precautions for the clamp meter
(1) The voltage of the line under test is lower than the rated voltage of the clamp meter.
(2) When measuring the current of the high-voltage line, wear insulated gloves, wear insulated shoes, and stand on the insulating mat.
(3) The jaws should be closed tightly and cannot be charged for the range.
Second, the use of megohmmeter
When the megohmmeter is working, it generates high voltage itself, and the measuring object is electrical equipment, so it must be used correctly, otherwise it will cause personal or equipment accidents. Before using, you must first make the following preparations:
1. The power of the equipment under test must be cut off before the quantity is measured, and the ground should be short-circuited and discharged. The equipment must not be energized for measurement to ensure the safety of the person and equipment.
2. For equipment that may induce high voltage, the possibility must be eliminated before measurement can be made.
3. The surface of the object to be tested should be cleaned to reduce the contact resistance and ensure the correctness of the measurement results.
4. Before the measurement, check whether the megohmmeter is in normal working condition, mainly check the two points of “0†and “∞â€. That is, the handle is shaken to make the motor reach the rated speed. The megger should be in the “0†position when it is short-circuited and “∞†when it is open.
5. The megger should be placed in a stable and stable place and away from large external current conductors and external magnetic fields.
After the above preparations are made, the measurement can be carried out. When measuring, pay attention to the correct wiring of the megohmmeter, otherwise it will cause unnecessary errors or even errors.
There are three terminals of the megohmmeter: one is “Lâ€, that is, the line end, one “E†is the ground end, and another “G†is the shield end (also called the protection ring). Generally, the insulation resistances to be tested are connected. Between the "L" and "E" ends, but when the surface of the insulator to be tested is seriously leaky, the shield ring of the test object or the portion not to be measured must be connected to the "G" end. Thus, the leakage current flows directly back to the negative end of the generator via the shield end "G" to form a loop, rather than flowing through the megohmmeter measuring mechanism (moving coil). This fundamentally eliminates the influence of surface leakage current. In particular, it should be noted that when measuring the insulation resistance between the cable core and the outer surface, the shield terminal "G" must be connected because the air humidity is high or the cable is insulated. When the surface is not clean, the leakage current on the surface will be very large. In order to prevent the measured object from being affected by leakage, its internal insulation measurement is generally added to the outer surface of the cable with a metal shielding ring, and the megger of the megohmmeter. "End connected.
When using the megohmmeter to measure the insulation resistance of electrical equipment, be sure to note that the "L" and "E" ends cannot be reversed. The correct connection is: "L" line end button is connected to the conductor of the device under test, "E" The grounding device is grounded, and the “G†shield terminates the insulated part of the device under test. If the "L" and "E" are reversed, the leakage current flowing through the insulator and the surface is collected to the ground through the outer casing, and the ground flows through the "L" into the measuring coil, so that the "G" loses the shielding effect and gives the measuring tape. There is a big error. In addition, because the inner lead of the "E" end is insulated from the outer casing by a degree of insulation lower than the "L" end and the outer casing, when the megohmmeter is placed on the ground, when the correct wiring is used, the "E" end is opposite to the outer casing of the instrument. The insulation resistance of the shell to the ground is equivalent to a short circuit and does not cause an error. When the "L" and the "E" are reversed, the insulation resistance of the "E" to the ground is in parallel with the measured insulation resistance, and the measurement result is biased. Small, causing large errors in the measurement.
Third, exchange millivoltmeter use precautions
1. Short-circuit and zero adjustment before measurement. Turn on the power switch, clamp the red and black clips of the test line (also called the open cable), turn the range knob to the 1mv range, and the pointer should be at the zero position (some millivoltmeters can pass the zero potentiometer on the panel) For zero adjustment, if the panel has no zero potentiometer, the internal zero potentiometer has been adjusted). If the pointer does not point to the zero position, check the test line for open circuit or poor contact. Replace the test line.
2. The sensitivity of the AC millivoltmeter is high. After the power is turned on, the pointer will deflect due to the interference signal (sensing signal) at a lower range, which is called self-starting phenomenon. Therefore, when the signal is not tested, the range knob should be turned to the higher range to prevent the pointer from being bent.
3. When the AC millivoltmeter is connected to the circuit under test, its ground (black clip) should always be connected to the ground of the circuit (become a common ground) to prevent interference.
4. When adjusting the signal, first turn the range knob to a larger range, then change the signal and then gradually reduce it.
5. AC millivoltmeter dial scale is divided into 0-1 and 0-3 scales, range knob switching range is divided into every range (1mv, 10mv, 0.1v...) and every three ranges (3mv, 30mv, 0.3) v......), where the range of the scale is directly read on the 0-1 scale line, where the range of the third is directly read on the 0-3 scale line, the unit is the unit of the range, no conversion is required.
6. Before use, check whether the range knob and the range mark are consistent. If the position is wrong, the reading will be wrong.
7. The AC millivoltmeter can only be used to measure the rms value of a sinusoidal AC signal. If a non-sinusoidal AC signal is measured, it is converted.
8. Note: The AC voltage of the multimeter cannot be used instead of the AC millivoltmeter to measure the AC voltage (the internal resistance of the multimeter is low, which is used to measure the power frequency voltage of 50Hz or so).
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