How to use a multimeter to measure the quality of the inverter
For personal safety, it must be ensured that the machine is powered off, and the inverter input power lines R, S, T and output lines U, V, W must be removed before it can be operated! 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:
1. 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 display value on the multimeter; then touch the red test lead to N(-), and the black test lead to R, S, T in turn. T, record the display value of the multimeter; if the six display values are basically balanced, it indicates that there is no problem with the inverter diode rectifier or soft start resistor, otherwise the rectifier module or soft start resistor at the corresponding position is damaged, phenomenon: no display.
2. 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 touches U, V, W in turn. W, 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.
1. 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;
2. 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;
3. The minimum frequency can be calculated as follows: (synchronous speed - rated speed) × number of pole pairs p÷60. For example, for a 4-pole motor, the rated speed is 1470 revolutions, the minimum frequency = (1500-1470) × 2 ÷ 60 = 1Hz;
a. 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 with
"+", "-" symbols, and marked with "Dc input", "DC output" words. 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.
b. Distinguishment of input terminal and output terminal: Unmarked solid-state relay, multimeter R×10k range, by measuring the positive and negative resistance values of each pin to distinguish input terminal and output terminal. 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.
