Troubleshooting electric drive control circuit with multimeter
1. Measure the DC resistance value of components
In the electric drag control circuit, commonly used components are AC contactors, various relays, fuses, circuit breakers, control buttons, etc. We need to measure and record the DC resistance of AC contactor coils and various relay coils used in the circuit (the specific values are quite different for different types of contactors, such as the DC resistance of commonly used AC contactor coils is about 2000Ω, while the model is relatively small The new coil DC resistance is only a few hundred ohms).
2. Measure the continuity of the line
Before using the resistance method to find the fault point, first disconnect the two ends of the control circuit from the control power supply, and then place the multimeter in the R´10W or R´100W block for measurement. Generally, the method of section measurement is used to check whether the line is faulty.
3. Inspection of the control loop
Generally, the two test leads of the multimeter are respectively connected to the starting point of the control circuit, that is, U11 and V11 of FU2 (or the outlet points 0 and 1 of FU2), and press buttons, contactor position switches and other components to simulate control components. According to the on-off of each branch, the controlled contactor coil and relay coil are connected in parallel or disconnected, and the line is judged from the change of resistance indicated by the multimeter to determine whether the line is normal.
The button function, contactor self-locking function, contactor interlocking function and the main circuit can be measured separately. Connect the two test leads of the multimeter to the starting point of the control circuit, which is U11 and V11 of FU2. The reading of the multimeter is indicated as ∞ (If the resistance is 0Ω, there is a short circuit in the circuit; if the resistance is 2000Ω or 1000Ω, the self-locking contact or the start button may be connected incorrectly).
4. Inspection of the main circuit
Generally, it is carried out after the control circuit is checked. The main purpose is to check whether there is a short circuit in the main circuit. When checking the main circuit, because the DC resistance of each phase winding of the motor is small, generally below 10Ω, the resistance block should be selected as ×1Ω. After connecting the motor, press the contactor contact bracket according to the working order of each contactor to simulate the contactor work, and at the same time use a multimeter to measure the resistance between the outlet points U11, V11 and W11 of the main switch. The resistances should be equal and belong to the motor. Resistance between any two power leads. If the resistance is zero, it means that there is a short circuit in the main circuit; if the resistance is large or ∞, it means that the main circuit has poor contact or open circuit.
After measurement, if the resistance value conforms to the above rules, the circuit wiring is basically correct and there is no serious fault (short circuit), and the success rate of power-on is very high. At the same time, the level of analysis and judgment of the circuit is also improved during the measurement process.
Choose the appropriate gear for the multimeter. If the gear is too high, the reading will be too small, and it will be misjudged as a short circuit. If the gear is too small, the reading will be large, and it will be misjudged as an open circuit, which will seriously affect the accuracy of the measurement. Generally, choose ×10Ω block or ×100Ω block.
After turning on the power and before turning on the power for a test run, you should use the voltage measurement method to measure whether the output voltage of each fuse is normal. If it is not normal, find out the reason; when the control circuit can be controlled normally, you must measure the output voltage of the power output terminal connected to the motor. Check whether the voltage is normal to avoid phase loss when the motor is energized.
