The skill of measuring the quality of the frequency converter with a multimeter
It should be noted that for personal safety, the machine must be powered off, and the inverter input power lines R, S, T and output lines U, V, W must be removed before operation! First turn the multimeter to the "secondary tube" file, and then use the red and black test leads of the multimeter to detect according to the following steps:
The black test lead touches the negative pole P (+) of the DC bus, the red test lead touches R, S, T in turn, and records the displayed value on the multimeter. Then touch the red test lead to N (-), and the black test lead to R, S, T in turn, and record the display value of the multimeter. If the six display values are basically balanced, it means that there is no problem with the diode rectification or soft-start resistor of the inverter, otherwise the rectifier module or soft-start resistor at the corresponding position is damaged. Phenomenon: no display.
The red test lead touches the negative pole P (+) of the DC bus, the black test lead touches U, V, W in turn, and records the displayed value on the multimeter. Then touch the black test lead to N (-), and the red test lead to U, V, W in turn, and record the display value of the multimeter. If the six display values are basically balanced, it indicates that there is no problem with the IGBT inverter module of the frequency converter. Otherwise, the IGBT inverter module at the corresponding position is damaged. Phenomenon: no output or a fault is reported.
Use the frequency converter to drive an asynchronous motor with matching power to run without load, adjust the frequency f, and start to drop from 50Hz to the lowest frequency.
During this process, use an ammeter to detect the no-load current of the motor. If the no-load current is stable during the frequency drop process and can remain basically unchanged, it is a good inverter.
The minimum frequency can be calculated like this, (synchronous speed - rated speed) × number of pole pairs p÷60. For example, for a 4-pole motor, the rated speed is 1470 revolutions, and the minimum frequency = (1500-1470) × 2÷60 = 1Hz.
Discrimination of AC and DC solid state relays: Usually, beside the input and output terminals of the DC solid state relay casing, there are marked "+" and "-" symbols, and the words "Dc input" and "DC output" are marked. The AC solid state relay can only be marked with "+" and "-" symbols on the input end, and the output end has no positive and negative points.
Discrimination of input and output terminals: unmarked solid-state relays, multimeter R×10k files, by measuring the forward and reverse resistance values of each pin to determine the input and output terminals. When the forward resistance of a certain two pins is small and the reverse resistance is infinite, these two pins are input terminals, and the other two pins are output terminals. In a measurement with a small resistance value, the black test lead is connected to the positive input terminal, and the red test lead is connected to the negative input terminal.
If the measured forward and reverse resistances of a certain two pins are both 0, it means that the solid state relay has been broken down and damaged. If the measured forward and reverse resistance values of each pin of the solid state relay are infinite, it means that the solid state relay has been damaged by an open circuit.
