1. Correct Use of the Multimeter
To use the multimeter correctly, familiarize yourself with the dial. Adjust the two zero position regulators gently. Choose the correct terminals, ensuring the red and black probes are inserted into the right holes.
Turn the switch to the correct range. Select the appropriate measurement range for accurate readings. Ensure you are looking at the scale correctly, reading the display straight on.
After measuring, switch the probes back to the high voltage range. Regularly check the internal battery, as deterioration can lead to electrolyte leakage. Store the instrument in a good environment, free from vibration, humidity, and weak magnetic fields.
2. Proper Use of the Ohm Range on the Multimeter
To use the ohm range correctly, there are eight key points to know. Ensure the battery voltage is sufficient and that the circuit being tested is de-energized. Select the appropriate range, aiming for the middle of the scale.
Each time you change the range, you must recalibrate the zero resistance. Ensure good contact at the probe tips, and do not touch the probe ends with your hands. For continuity testing, use a range above one thousand ohms.
When testing diodes, different ranges will yield different resistances. When measuring transformer windings, avoid touching them as it may cause electric shock.
3. Important Notes When Measuring Voltage with a Multimeter
When measuring voltage with a multimeter, there are eight important notes. Be aware of the internal resistance of the meter, and ensure someone is monitoring the process. The multimeter should be connected in parallel with the live circuit, and do not change the range while powered.
When measuring DC voltage, clarify the polarity of the circuit. For measuring reactive circuits, do not disconnect the power supply during the measurement. For testing high voltage (kilovolt), use specialized probe leads.
Induced voltage measurements can vary significantly depending on the range used.
4. Methods for Measuring DC Current with a Multimeter
To measure current with a multimeter, set the switch to the milliamp range, confirm the polarity of the circuit, and connect the meter in series with the circuit. Choose a higher range to minimize the impact on the circuit.
5. Using DC Methods to Identify the Ends of a Three-Phase Motor Stator Winding
To identify the ends of a three-phase motor winding, use the DC method. Set the multimeter to the milliamp range and use a DC power source like a battery. Connect one phase winding to the meter and the other to the battery.
When powered, if the needle moves, the positive and negative terminals are identified. If it does not reverse, switch the connections and test the remaining phase winding.
6. Using Residual Magnetism to Identify the Ends of a Three-Phase Motor Stator Winding
For a motor that has been in operation, use the residual magnetism method. Mark the output terminals of the three-phase windings and connect them in parallel. Set the multimeter to the milliamp range and connect to the common point.
Slowly rotate the motor shaft while observing the meter needle. If the needle does not move significantly, the three ends are connected together. If the needle swings left and right, it indicates two ends are connected to one end.
Switch the leads of one phase winding and repeat the test until the needle stabilizes, indicating the ends are connected correctly.
7. Using the Loop Method to Identify the Ends of a Three-Phase Motor Stator Winding
For a motor that has been in operation, use the loop method. Connect the three-phase windings in a triangle configuration. Set the multimeter to the milliamp range and connect it in series with the three-phase windings.
Rotate the motor shaft evenly while observing the meter needle. If the needle does not move significantly, the ends of the windings are connected. If the needle swings widely, one phase winding is reversed.
Two connection points indicate the start and end of the windings.
8. Measuring the Speed of a Three-Phase Motor with a Multimeter
To measure the speed of a three-phase motor, open the motor junction box and disconnect the terminal connections. Set the multimeter to the milliamp range and connect it to any phase winding.
Rotate the rotor for one complete turn and observe how many times the needle moves. A two-pole motor will show one swing, indicating a synchronous speed of three thousand RPM. A four-pole motor will show two swings, indicating a synchronous speed of one thousand five hundred RPM.
Continue this method to determine the speed, which will be slightly lower than the synchronous speed.
9. Testing the Ground Resistance of Household Grounding Protection Lines
To test the ground resistance of household grounding lines, set the multimeter to the voltage range and connect a kilowatt electric stove to the phase and neutral. Measure the voltage at the stove terminals to calculate the working current value.
Reconnect the stove to the ground line and measure the voltage again. The difference in voltage readings divided by the working current value gives the ground resistance, with an approximate error of five percent.
10. Identifying Phase and Neutral Wires in Low Voltage AC Power Supply
In a low voltage three-phase four-wire system, identify the phase and neutral wires. Set the multimeter to the voltage range, with a range of 250V AC. Connect one probe to the ground and the other to the power line.
If the needle deflects significantly, the probe is touching the phase wire. If the needle does not move or only slightly deflects, the probe is touching the neutral wire.
11. Testing the Polarity and Condition of a Diode
To test the polarity of a diode, set the multimeter to the kilo-ohm range. A reading below one thousand ohms indicates forward resistance. Connect the black probe to the anode and the red probe to the cathode.
A reading of several thousand ohms indicates reverse resistance. Connect the red probe to the anode and the black probe to the cathode.
To determine if the diode is good, set the multimeter to the kilo-ohm range. A significant difference between forward and reverse resistance indicates a good diode. If the values are close, the diode is likely faulty.
A reading of zero indicates a short circuit between the two terminals, while an infinite reading indicates an open circuit inside the diode.
12. Testing the Condition of a High Voltage Silicon Stack
To check the condition of a silicon stack, set the multimeter to the voltage range. Connect the silicon stack in series with the multimeter and apply 220V AC. Set the DC range to 250V and connect the silicon stack in the forward direction.
A reading above thirty volts indicates it is functioning correctly; if the needle does not move, there is a fault. A reading of 220V AC indicates a short circuit, while a reading of zero indicates an open circuit inside the silicon stack.
13. Testing the Condition of a Capacitor
To test the condition of a microfarad capacitor, set the multimeter to the kilo-ohm range and connect the probes to the terminals. The needle should swing left and right; the greater the swing, the better the capacitor.
If the needle does not move, the capacitor is open. If the needle drops to zero and does not return, the capacitor has shorted.
14. Using a Digital Multimeter’s Buzzer Function to Test Electrolytic Capacitor Quality
To test the quality of an electrolytic capacitor, set the digital multimeter to the buzzer function and connect the probes to the positive and negative terminals. A short beep indicates the capacitor is functioning, while a continuous beep indicates a short circuit. If there is no sound, the capacitor is open.
15. Safety Regulations When Using a Clamp Meter
When using a clamp meter, remember the safety regulations. Testing high voltage circuits must be done by two people. The potential of the wire being tested must not exceed the voltage rating of the clamp meter.
Always wear gloves and stand on an insulated platform. Maintain a safe distance from any live parts. When measuring low voltage bus currents, ensure proper insulation and protection.
Do not use the clamp meter on poorly insulated or bare wires.
16. Correct Use of a Clamp Meter
When using a clamp meter, select the appropriate model and specifications. Start with the maximum range for rough measurements, then select the appropriate range. Position the wire in the center of the clamp jaws, ensuring a good fit.
Once the clamp is closed around the wire, do not change the range while powered. Clamp meters measure current and voltage separately. Do not insert both wires of a lighting circuit into the clamp at the same time.
After each test, return the range to the maximum setting.
17. Techniques for Measuring Three-Phase Three-Wire Current with a Clamp Meter
To measure three-phase three-wire current with a clamp meter, apply Kirchhoff’s law. Insert the clamp around one wire to read the current of that phase.
Insert the clamp around two wires to read the current of the third phase. If the clamp is around all three wires, the reading should be zero, indicating balanced load.
18. Techniques for Measuring Small AC Current with a Clamp Meter
To measure small AC currents with a clamp meter, wrap the insulated wire around the clamp’s core. Divide the reading by the number of turns plus one to obtain the actual current value.
19. Detecting Phase Loss Faults in a Three-Phase Resistance Furnace
To detect phase loss in a three-phase resistance furnace, use a clamp meter. If the current in two phase wires is below the rated current and one phase wire shows zero current, that phase’s resistance wire is burnt out.
20. Locating Short Circuit Ground Faults in Low Voltage Distribution Lines
In long low voltage distribution lines, locating short circuit ground faults can be challenging. If a fault phase wire is connected to an electric stove, use a single-pole switch to connect to the power supply. Use a clamp meter to measure the current in segments of the line.
The point where the current changes indicates the location of the short circuit.
21. Testing Thyristor Rectifier Devices
To test thyristor rectifier devices, use a clamp meter. Connect the clamp to the anode connection and observe the current reading. A reading of zero indicates the component is not functioning.
For three-phase components, the current values should be balanced. Significant imbalance indicates phase shifting issues. If there are faults in the AC section, the rectifier transformer may be missing a phase.
22. Detecting User Phase Theft
If a user’s single-phase energy meter shows low or no readings, use a clamp meter to check before and after the meter. If the clamp is around the phase and neutral wires, the reading should not be zero.
If the readings differ significantly between the phase and neutral wires, it indicates phase theft, typically one phase stealing from the ground.
23. Safety Regulations When Using an Insulation Resistance Tester
When using an insulation resistance tester, adhere to safety regulations. Testing high voltage equipment must be done by two people. Ensure the equipment is fully powered down and properly discharged.
When measuring insulation on lines, obtain permission from the other party. Both circuits must be powered down, and testing should not occur during thunderstorms. Maintain a safe distance from live equipment.
Ensure adequate safety measures are in place to prevent electric shock.
24. Correct Use of an Insulation Resistance Tester
When using an insulation resistance tester, select the appropriate voltage level. Ensure the equipment is powered down and properly discharged before testing. Clean the surface of the equipment to remove any dirt or contaminants.
Position the tester appropriately, away from electric and magnetic fields. Keep it level and perform both open and short circuit tests. Use two insulated single-core leads that do not tangle.
Ensure the connection terminals are clearly identified and connected correctly. Rotate the handle clockwise to gradually reach a constant speed. There is no fixed time for testing; record the reading when the needle stabilizes.
25. Important Considerations When Using an Insulation Resistance Tester
When using an insulation resistance tester, remember these eight important considerations. Do not touch the connection terminals during testing. Avoid cleaning the meter’s glass during the testing process.
When testing insulation to ground, connect the ground terminal to the outer casing. For large capacitive devices, disconnect at rated speed. When testing electrolytic capacitors, connect the ground terminal to the positive terminal.
For repeated tests on the same device, it is best to use the same meter. Record the temperature during insulation testing. Do not test resistances below one hundred kilo-ohms, and do not use the meter for continuity testing.
26. Connecting a Diode in Series to Prevent Discharge from the Device Being Tested
To prevent the device being tested from discharging the insulation resistance tester, connect a diode in series with the tester. This will help stabilize the reading and ensure accurate measurements.
After testing, stop rotating the handle to avoid damaging the instrument.
27. Methods to Increase the Voltage of an Insulation Resistance Tester
For low voltage insulation resistance testers, connect them in series to increase the testing voltage. The total voltage will be the sum of the individual testers.
28. Insulation Absorption Ratio of Power Transformers
The quality of transformer insulation can be assessed using an insulation resistance tester. At a standard temperature of around twenty degrees Celsius, start timing from the moment of measurement: check the reading at fifteen seconds and stabilize the value after a few seconds.
The ratio of the two insulation resistance values is called the insulation absorption ratio. A value greater than 1.3 is considered good, while a value below 1.3 indicates moisture.
29. Quickly Assessing the Condition of Low Voltage Motors
To quickly assess the condition of low voltage motors, open the junction box for testing. Use an insulation resistance tester to measure the minimum insulation resistance value, using thirty-five degrees Celsius as a reference, reducing by half for every ten degrees increase.
For every ten degrees decrease, double the reading to determine if it is acceptable. Set the multimeter to the milliamp range and use the star connection method. Connect the probes to any two phase terminals and slowly rotate the shaft.
If the needle swings significantly, repeat the test three times for consistent results. If the motor is good, it will function; otherwise, it is faulty.
30. Testing the Condition of High Voltage Silicon Stacks with an Insulation Resistance Tester
To test the condition of high voltage silicon stacks, use an insulation resistance tester. Connect the two leads to the silicon stack terminals. Measure the forward and reverse resistance; a significant difference indicates a good stack.
If the readings are close, the silicon stack is likely faulty. If both readings are infinite, the stack is open. If both readings are close to zero, the stack has shorted.
31. Testing the Condition of Self-Ballasted High Voltage Mercury Lamps with an Insulation Resistance Tester
To test the condition of high voltage mercury lamps, use a kilovolt insulation resistance tester. Connect the leads to the lamp terminals. Test in a dim environment, gradually increasing the speed of the tester.
A reading below half a megaohm indicates the lamp is functioning. If the lamp does not light, the reading will be zero, indicating a short circuit. An infinite reading indicates an open circuit fault.
32. Testing the Quality of Fluorescent Tubes with an Insulation Resistance Tester
To test the quality of fluorescent tubes, use a kilovolt insulation resistance tester. Set the multimeter to the voltage range with a setting of 500V DC. Connect the multimeter in parallel, ensuring the polarity is correct.
Connect the leads to the ends of the tube. The lamp should light at rated speed; below three hundred volts is normal. If the lamp glows slightly, it indicates aging above three hundred volts.
If the lamp does not light at all, it indicates the tube is damaged.
33. Testing the Quality of Fluorescent Lamp Starters with an Insulation Resistance Tester
To test the quality of fluorescent lamp starters, use an insulation resistance tester. Connect the leads to the starter terminals. Slowly and gently rotate the handle; the neon bulb should flash red.
If the starter is functioning well, it will work; otherwise, it is faulty.
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