Measure electricity

Visualizing electricity with instruments

Measure Voltage

The learning kit includes an voltmeter and an ammeter. Since they operate in very different manners, make sure you use the correct one for the measurements. We start with voltage measurement. To measure voltage, we are going to use the blue voltmeter.

Preparing Device

Before connecting a voltmeter to a circuit, the voltmeter should be set to its maximum range first. For the voltmeter in this experiment, there is a toggle switch at the bottom of the panel. This voltmeter only has two ranges, 0 - 3 V and 0 - 15 V. Switch it to the side with the printed number β€œ15”.

Be Aware to Polarity

It is notable that the voltmeter also has a β€œ+” and β€œ-” symbols. These symbols indicate the default polarity of the voltmeter while interpreting the measured voltages. This means when connecting a voltmeter to a circuit, you are recommended to connect the meter’s positive polarity to the higher voltage terminal of the circuit being measured whereas the negative polarity connects to the lower voltage terminal.

Testing & Reading

Recall our discussion on voltage polarities earlier. Reversing the polarity of measurement may yield a negative reading on the meter, indicating a voltage drop with the opposite sign to the actual measurement. However, some analog voltmeters lack a scale to the left of 0 and are not intended to read negative voltages. In such cases, reversing the polarity of the measured voltage will not cause the needle to move into a negative range. Instead, the needle will either remain at 0 or may deflect slightly due to internal structure, but it does not provide a meaningful measurement.

When using a voltmeter for testing, it is always recommended to start with the highest range setting (15V for our voltmeter) if you are unsure about the possible voltage range being measured. This is to prevent over-ranging, which can potentially damage the meter. Once you have confirmed that the voltage is within a lower range, you can then adjust the voltmeter to that range for a more precise reading.

After connecting the two test probes in parallel to the two terminals of the device to be measured, the readout on the voltmeter is the voltage difference (or voltage drop) across the two terminals you measured.

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