The use of a multimeter for the measurement of good and bad inverters
For personal safety, we must ensure that the machine is disconnected from the power supply, and remove the inverter input power lines R, S, T and output lines U, V, W and then put into operation! First of all, the multimeter to "secondary tube" file, and then through the multimeter's red pen and black pen according to the following steps to detect:
First, the black pen contact DC bus negative P (+), the red pen contact R, S, T, record the display value of the multimeter; and then the red pen contact N (-), the black pen contact R, S, T, record the display value of the multimeter; six times the display value of the basic balance, it shows that the diode rectifier inverter diode or soft-start resistor is no problem, and vice versa, the corresponding position of the rectifier module or soft start Resistor damage, phenomenon: no display.
Second, the red pen contact DC bus negative P (+), the black pen contact U, V, W, record the multimeter display value; and then the black pen contact N (-), the red pen contact U, V, W, record the display value of the multimeter; six display value if the basic balance, it indicates that the frequency converter IGBT inverter module is no problem, on the contrary, the corresponding position of the IGBT inverter module Damage, phenomenon: no output or report fault.
1. Use the inverter to drag a power-matched asynchronous motor running at no load, adjust the frequency f, from 50Hz down to the lowest frequency;
2. In this process with an ammeter to detect the motor no-load current, if the no-load current in the frequency drop process is very smooth, can remain basically unchanged, that is a good inverter;
3. The minimum frequency can be calculated like this, (synchronous speed - rated speed) × pole pair number p ÷ 60. For example, a 4-pole motor, rated speed is 1470 rpm, the minimum frequency = (1500-1470) × 2 ÷ 60 = 1Hz;
a. AC and DC solid state relay discrimination: usually, next to the input and output terminals of the DC solid state relay case, there are marked with
"+", "-" symbol, and marked with "Dc input", "DC output" words. AC solid state relays can only be marked on the input side of the "+", "-" symbols, the output side of no positive, negative points.
b. Identification of input and output: For solid state relays without marking, the multimeter with R×10 k gear can be used to identify the input and output by measuring the positive and negative resistance values of each pin respectively. When the forward resistance of two pins is small and the reverse resistance is infinite, these two pins are the inputs and the remaining two pins are the outputs. In a smaller resistance measurement, the black pen is connected to the positive input, the red pen is connected to the negative input.
If the positive and reverse resistance of the two pins are measured to be 0, it means that the solid state relay has been damaged. If the positive and negative resistance values of each pin of the solid state relay are infinity, it means that the solid state relay has been damaged by open circuit.
