How to measure the quality of soft start thyristor

Soft-start thyristor is a power electronic device used to control the start and operation of the motor. It has the advantages of smooth start, high operating efficiency and convenient control. In practical applications, the measurement of soft-start thyristor is of great significance to ensure the normal operation of the motor and extend the life of the equipment. This article will introduce the measurement method and precautions of soft-start thyristor in detail to help users accurately judge the quality of thyristor.

1. Working principle of soft start thyristor

The soft-start thyristor is a three-terminal bidirectional thyristor device, whose internal structure consists of three PN junctions, namely the anode, cathode and gate. When a positive voltage is applied to the gate, the thyristor is turned on and the current flows from the anode to the cathode; when the gate voltage disappears, the thyristor is turned off and the current stops flowing. The turn-on and turn-off characteristics of the soft-start thyristor make it play an important role in the starting and running process of the motor.

2. Measurement method of soft start thyristor

1. Appearance inspection

First, perform an appearance inspection on the soft start thyristor to see if there are any abnormalities on its surface, such as cracks, ablation, deformation, etc. If any abnormality is found, it means that the thyristor may be damaged and further inspection is required.

1. Measuring forward conduction characteristics

Use the diode measurement function of the multimeter, connect the red test lead to the anode of the thyristor, the black test lead to the cathode, and measure the forward conduction voltage. Under normal circumstances, the forward conduction voltage of the thyristor should be around 0.7V. If the measurement result deviates from the normal value, it means that there may be a problem with the thyristor.

1. Measuring reverse blocking characteristics

Connect the red test lead of the multimeter to the cathode of the thyristor and the black test lead to the anode, and measure the reverse blocking voltage. Under normal circumstances, the reverse blocking voltage of the thyristor should be greater than or equal to 1000V. If the measurement result is lower than 1000V, it means that the reverse blocking performance of the thyristor has deteriorated and it may be damaged.

1. Measuring gate trigger characteristics

Use the diode measurement function of the multimeter to connect the red test lead to the gate of the thyristor and the black test lead to the cathode to measure the gate trigger voltage. Under normal circumstances, the gate trigger voltage of the thyristor should be around 5V. If the measurement result deviates from the normal value, it means that the gate trigger performance of the thyristor has deteriorated and may be damaged.

1. Measuring the on-resistance of thyristors

Use the resistance measurement function of the multimeter to connect the red test lead to the anode of the thyristor and the black test lead to the cathode to measure the on-resistance of the thyristor. Under normal circumstances, the on-resistance of the thyristor should be below 10mΩ. If the measurement result is higher than 10mΩ, it means that the conduction performance of the thyristor has decreased and it may be damaged.

1. Measuring the turn-off time of thyristors

Use an oscilloscope to measure the turn-off time of the thyristor. Connect the probe of the oscilloscope between the anode and cathode of the thyristor, and select the gate voltage signal of the thyristor as the trigger source. Observe the waveform on the oscilloscope and measure the time from the thyristor being turned on to being turned off. Under normal circumstances, the turn-off time of the thyristor should be less than 10μs. If the measurement result is higher than 10μs, it means that the turn-off performance of the thyristor has degraded and it may be damaged.

1. Measuring thermal performance of thyristors

Use a thermal imager to measure the surface temperature of the thyristor under normal working conditions. Under normal circumstances, the surface temperature of the thyristor should be lower than 80°C. If the measurement result is higher than 80°C, it means that the heat dissipation performance of the thyristor has decreased and it may be damaged.

3. Precautions for soft start thyristor

1. During the measurement process, ensure that the range and accuracy of the multimeter and oscilloscope meet the requirements to avoid measurement errors.

2. When measuring the forward conduction characteristics and reverse blocking characteristics of a thyristor, be careful not to apply voltage for a long time to avoid damaging the thyristor.

3. When measuring the gate trigger characteristics of a thyristor, pay attention to controlling the gate voltage to avoid exceeding the rated voltage of the thyristor.

4. When measuring the on-resistance of a thyristor, be sure to select the appropriate resistance measurement position to avoid measurement errors.

5. When measuring the turn-off time of the thyristor, pay attention to selecting the appropriate oscilloscope time and voltage range to clearly observe the waveform.

6. When measuring the thermal performance of thyristors, pay attention to selecting an appropriate thermal imager and measurement environment to ensure the accuracy of the measurement results.

7. During the measurement process, pay attention to safe operation and avoid dangers such as electric shock and short circuit.

Through the above detailed measurement methods and precautions, users can accurately judge the quality of soft start thyristors, thereby ensuring the normal operation of the motor and extending the life of the equipment. In practical applications, users should choose appropriate measurement methods and tools according to specific circumstances to ensure the accuracy and reliability of the measurement results.