Circuit Testing with a Multimeter
A Multitester Performs Analog and Digital Electrical Troubleshooting
For circuit board testing or electronic testing, a multimeter is the test equipment of choice. Also called a volt ohm meter, the analog model needs a meter calibration.
When doing any kind of electrical troubleshooting, part of the procedure is circuit testing with a multimeter. Sometimes called a multitester, this tool performs many different types of diagnostic testing. They are now so commonplace and there are so many manufacturers that any DIYer should have one in the tool box.
Types of Multimeters
There are two basic types – the earlier analog multimeter, and the more modern digital multimeter. Some call this tool a volt ohm meter. The many different names indicates that in fact, it's capable of performing many different tasks; and all in a small package!
This article describes these two types of test equipment, and walks through two common types of electronic circuit tests.
Analog Multimeter
Analog multimeters are very easy to recognize – There's a large square or rectangular gauge with various scales on it. A needle centered at the bottom sweeps from left to right to give a reading on the test being conducted.
An analog meter must undergo a meter calibration before use. First, connect the black cable to the negative (common) jack on the meter. Then connect the red cable to the positive jack. Touch the two probes together. The idea is for the gauge needle to sweep across to the right and center over ZERO. If it doesn't, simply use the adjustment dial. If it still won't calibrate, change the batteries.
Digital Multimeter
The digital multimeter isn't as classically science fiction-looking as its analog cousin; think modern. The display looks similar to an appliance clock. There usually isn't any meter calibration to do; if anything, check the documentation.
Whichever type of multitester is being used, both perform various electrical troubleshooting tests.
Meters as Continuity Testers
The continuity test is arguably the most basic electrical test done with this diagnostic tool. Continuity just means that there is no break in a part of the electrical circuit; the juice is getting from point A to point B as designed.
With an analog multitester, set the selector control knob to RX1. Touch one probe to point A and the other to point B. If the needle swings to zero ohms, there is continuity. If it stays on infinite ohms, there isn't.
With a digital unit, put the function control on OHMS and the range control to the lowest setting. Touch the probes as above. If it beeps or the display says 0.00, continuity exists.
Meters as Voltage Testers
When testing a motor not connected to a circuit board or a transformer with an analog unit, the selector control should be set at 50 ACV. (DCV if testing a thermocouple or motor hooked up to a circuit board.) Turn off all power on the unit to be tested.
Use the cables configured with alligator clips; clip them to the terminals. Turn on the juice and the multitester needle will peg on the voltage.
When testing a transformer with a digital multimeter, set range control to 30 and function control to ATV. Turn off power to the transformer, connect the alligator clips, turn on the juice, and the power will be displayed.
