Multimeter

A multimeter, also known as a Volt-Ohm-Milliameter, is an electronic measuring instrument that is typically used to measure voltage, current, and resistance. There are analog multimeters that operate by moving a pointer to display the measurement, but today most multimeters are digital with an LCD that is used to display exactly what the measurement is.

A multimeter can cost as low as USD $10 and up to USD $400 for a really nice Fluke 87V. Unless you are planning on using the multimeter for professional purposes, I would recommend getting a low-cost multimeter like the ones shown in the following photograph:

The digital multimeter has three main parts, which are the display, selection knob, and the probe ports.

The display will show what the measurement is. Some of the higher-end multimeters have a backlit display to make it easier to read in low light.

The selection knob is used to select what we wish to measure. Most multimeters will read resistance (ohms), voltage (volts), and current (amps). Some of the higher-end meters will have the ability to measure additional items and have additional features.

Probes are plugged into the probe ports, which are usually located on the front of the meter. The black probe should be plugged into the port labeled COM and the red probe will be plugged into one of the other ports depending on what is being measured. Really there is no difference between the red and black probes; however, it is good practice to always connect black probes and wires to common/ground and the red probes and wires to power since this is the standard.

Digital multimeters are very easy to use. We start off by selecting what we wish to measure using the selection knob. Then connect the black probe to one end of the circuit and the red probe to the other and the multimeter will display the measurement. The following photograph shows how we would measure the remaining voltage of a 9V battery:

You will notice that the selector knob is set to 20V, therefore, the meter will measure up to 20V. The following photograph shows how we could measure the resistance of a resistor:

In this photograph, we are measuring a 330K Ohm resistor. If we happen to set the selection knob to low, we would overload the multimeter but almost all meters have protection, therefore, they will not be damaged by overloading them. When you overload a meter they typically show a 1 all the way to the left of the display as the following photograph shows:

In the preceding photograph, we are trying to measure a 330K Ohm resistor with the selection knob set for a maximum of 200K Ohms. If you are not comfortable using a multimeter I would recommend searching for multimeter video tutorials and watching a couple videos on how to use them.