12.4: Introduction to voltage measurements
Voltage measurements are very easy to make with a DMM. On meters with manual range selection, start with a value one setting higher than expected. An autorange DMM will automatically select the range based on the voltage present. Figure \(\PageIndex{1}\) shows the process.
\[\begin{array}{l}{\dfrac{1}{1000} V=1 \mathrm{mV}} \\ {1000 \mathrm{V}=1 \mathrm{kV}}\end{array}\]
Follow these steps to measure voltage:
- Select the DC or AC volts function by turning the function switch to DC or AC volts.
- Plug the test probes into the appropriate probe jacks.
- Connect the tips of the probes across the source or load.
- View the reading on the display unit. Be sure to note the unit of measurement. If you are testing DC voltage and a negative sign appears in the display, the polarity of your probes is incorrect and needs to be reversed.
Use the one-hand technique. Attach test leads one at a time using only one hand. Put your other hand in a pocket or behind your back. Whatever you choose to do with your other hand, keep it well away from a live circuit or associated equipment. Avoid holding test leads in both hands. The one-hand technique decreases the possibility of a dangerous electrical shock by reducing the chance of current flowing through your body across your chest.
Autoranging units display the unit of measurement in the top right corner (annunciator). In manual ranging units, the meter will use the range selected. Autorange will determine the highest setting and automatically display that unit.