Measuring load current involves inserting a meter, typically a multimeter configured as an ammeter, directly into the path of the current flowing through the load. This requires the meter to be connected in series with the load so that the current flows through the meter.
Steps to Measure Load Current with a Multimeter
Using a multimeter to measure current means the circuit must be broken or interrupted to insert the meter. As demonstrated in the reference, you place the meter probes between the components to measure the current flowing between them.
Here's a general approach:
- Prepare the Circuit: Ensure the circuit is powered off. Identify the load (the component you want to measure current through) and the points in the circuit where current enters and leaves the load.
- Break the Circuit: Physically disconnect the wire or connection point on one side of the load. This creates an opening in the circuit.
- Configure the Multimeter:
- Select the current measurement function on your multimeter (usually marked with 'A' for Amperes or 'mA' for milliAmperes).
- Choose the appropriate range. Start with the highest range if you don't know the expected current to avoid damaging the meter, then decrease it for a more accurate reading if necessary.
- Move the positive (red) probe lead to the current input jack on the multimeter. This jack is often labeled 'A', 'mA', or has a maximum current rating (e.g., '10A', '300mA').
- Keep the negative (black) probe lead in the common ('COM') jack.
- Connect the Multimeter In Series:
- Connect the positive (red) probe from the multimeter to the point where the current leaves the power source or enters the load.
- Connect the negative (black) probe from the multimeter to the other side of the break in the circuit, where the current would normally flow from the load back towards the power source or ground.
- Reference Insight: As shown, this might involve "moving the resistor lead over a couple rows. Then connect one probe to the resistor. And one to the LED," effectively placing the meter between the resistor and the LED in series with them.
- Apply Power: Safely turn on the circuit's power.
- Read the Measurement: Observe the current reading displayed on the multimeter screen.
- Turn Off Power: Always turn off the circuit power before disconnecting the multimeter.
- Restore the Circuit: Reconnect the original wire or connection point to restore the circuit to its normal operating configuration.
Important Considerations:
- Series Connection: Ammeters must be connected in series. Connecting an ammeter in parallel across a voltage source or component will likely damage the meter (due to its very low internal resistance).
- Multimeter Ratings: Be aware of the maximum current rating of your multimeter and the selected range. Exceeding the rating can blow internal fuses or damage the meter.
- Circuit Interruption: Measuring current directly requires altering the circuit, which can be inconvenient or impossible in some situations.
Measuring current directly with a multimeter is a fundamental technique for understanding how much current a specific load is drawing from a power source.
