Inrush Current Measurement: Methods And Best Practices

Inrush current measurement refers to the measurement of the sudden increase in current (usually a peak current within a short period) in a circuit. Inrush current typically occurs during device startup, switch-on, or other instantaneous changes. This peak current can be significantly higher than the normal operating current of the device, making it crucial for the design and protection of electronic devices.

Steps for Measuring Inrush Current:

1. Determine the Measurement Point: Select a point in the circuit where inrush current is likely to occur, such as the power input or a critical location on the circuit board.

2. Choose the Appropriate Measuring Equipment:
- Oscilloscope: An oscilloscope can capture and display the waveform of the inrush current, helping to analyze the magnitude, duration, and shape of the current.
- Current Probe: Use a current probe with the appropriate range in conjunction with the oscilloscope to accurately capture the inrush current.

3. Set Measurement Parameters:
- Time Base: Ensure the oscilloscope's time base is fast enough to capture the rapid inrush current.
- Trigger Settings: Set the oscilloscope's trigger conditions to capture the moment when the inrush current occurs.

4. Perform the Measurement: Power on the circuit, observe the occurrence of inrush current, and record the waveform data.

5. Analyze the Waveform: Analyze the peak value, duration, and potential impact of the inrush current on the circuit. If the inrush current is too large, consider taking protective measures, such as adding surge protection devices (e.g., TVS diodes or varistors).

Considerations

- Protect Equipment: Ensure that both the circuit and the measuring equipment are protected from damage during the measurement, especially when dealing with high-power circuits.

- Inrush Current Standards: Check if the inrush current is within allowable limits based on device or industry standards.

By accurately measuring and analyzing inrush current, you can better design and protect electronic devices, reducing the risk of damage caused by inrush currents.