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How to measure the inverter with a multimeter
Aug 10, 2018

As we all know, the inverter has many protection functions, such as overcurrent, overvoltage, overload protection and so on. With the continuous improvement of industrial automation, inverters have also been widely used.


In the design process of electronic circuits, engineers inevitably need a multimeter to measure some measuring instruments. Engineers know that the multimeter can measure DC current, AC voltage, DC voltage. The inverter is a device that controls the AC motor by modifying the operating power frequency of the motor. This article will explain to you how to use a multimeter to measure the quality of the inverter.


It should be noted that for personal safety, it is necessary to ensure that the machine is powered off, and remove the inverter input power lines R, S, T and output lines U, V, W to operate! First, hit the multimeter into the “secondary tube” file, then use the red test pen and black test pen of the multimeter to check the following steps:


The black test lead contacts the negative pole P(+) of the DC bus, and the red test lead contacts R, S, and T in sequence to record the displayed value on the multimeter. Then touch the red test lead to N(-), and the black test lead touches R, S, and T in turn to 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 rectification or soft-start resistance, otherwise the rectifier module or soft-start resistor at the corresponding position is damaged. Phenomenon: No display.


The red test lead contacts the negative pole P(+) of the DC bus, and the black test lead contacts U, V, and W in sequence to record the displayed value on the multimeter. Then touch the black test lead to N(-), and the red test lead touches U, V, and W in sequence to record the display value of the multimeter. If the display value of the six times is basically balanced, it indicates that there is no problem with the IGBT inverter module of the inverter, and vice versa, the IGBT inverter module of the corresponding position is damaged. Phenomenon: no output or failure.


Use the inverter to drag a power-matched asynchronous motor to run at no load, and adjust the frequency f from 50 Hz to the lowest frequency.


In this process, the current meter is used to detect the no-load current of the motor. If the no-load current is stable during the frequency drop and can be kept basically unchanged, it is a good inverter.


The lowest frequency can be calculated in this way (synchronous speed - rated speed) × pole pair p ÷ 60. For example, a 4-pole motor with a rated speed of 1470 rpm and a minimum frequency = (1500-1470) × 2 ÷ 60 = 1 Hz.


There is no problem with the soft start resistor, but the rectifier module or soft start resistor at the corresponding position is damaged. Phenomenon: No display.


The red test lead contacts the negative pole P(+) of the DC bus, and the black test lead contacts U, V, and W in sequence to record the displayed value on the multimeter. Then touch the black test lead to N(-), and the red test lead touches U, V, and W in sequence to record the display value of the multimeter. If the display value of the six times is basically balanced, it indicates that there is no problem with the IGBT inverter module of the inverter, and vice versa, the IGBT inverter module of the corresponding position is damaged. Phenomenon: no output or failure.


Use the inverter to drag a power-matched asynchronous motor to run at no load, and adjust the frequency f from 50 Hz to the lowest frequency.


In this process, the current meter is used to detect the no-load current of the motor. If the no-load current is stable during the frequency drop and can be kept basically unchanged, it is a good inverter.


The lowest frequency can be calculated in this way (synchronous speed - rated speed) × pole pair p ÷ 60. For example, a 4-pole motor with a rated speed of 1470 rpm and a minimum frequency = (1500-1470) × 2 ÷ 60 = 1 Hz.


Discrimination of AC and DC solid-state relays: Generally, the input and output ends of the DC solid-state relay housing are marked with the "+" and "-" symbols, and the words "Dc input" and "DC output" are marked. The AC solid state relay can only mark the "+" and "-" symbols on the input end, and there is no positive or negative output at the output end.


Discrimination between input and output: solid-state relay without identification, multimeter R × 10k file, determine the input and output terminals by measuring the positive and negative resistance values of each pin. When the forward resistance of a certain two pins is measured and the reverse resistance is infinite, the two pins are the input terminals, and the other two pins are the output terminals. In a measurement with a small resistance, the black meter is connected to the positive input, and the red meter is connected to the negative input.


If the positive and negative resistances of a certain two pins are both 0, the solid state relay has been broken and damaged. If the positive and negative resistance values of each pin of the solid state relay are measured to be infinite, the solid state relay is open circuit damaged.


This article tags: Elevator Elevator knowledge Elevator safety Elevator repair Elevator inverter

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