Welcome To G-TV Today I will be showing you how to use a digital
multimeter.
This style of multimeters has also been referred to as a DMM or as a DVOM in the case of digital
volt ohmmeters.
Typically multimeters can be used to measure voltage, current, and resistance with many
multimeters also including additional test functions for diodes and continuity.
Other multimeter measurement functions may include capacitance, conductance, decibels,
duty cycle, frequency, temperature, and inductance.
There are also multimeters with settings for light, pH levels, and relative humidity of
a room.* To best demonstrate these functions, I will
use a digital multimeter here from Fluke.
These digital multimeters have a dial to select the appropriate test functions.
First I will show voltage measurements by going to the V symbol.
There may be two of them, one for AC and one for DC.
The symbol with one solid line and a dotted line parallel to it is for DC voltage and
the V with a wave over it is for AC voltage.
Some meters may have an mV setting to check for millivolts and some may have numbers to
define a specific range for testing.
These ranges can be adjusted for allowing a more accurate reading.
Testing is usually conducted by test probes with the black being in the common and the
red plugging to the voltage port.
For DC testing, I will use the red probe on the positive side and the black probe on the
negative.
Using a battery as a reference where the positive and negative polarity is more distinct, I
can see how my reading can be made in this way.
Multimeters may also include a toggle function or mode button to access more functions on
a given selection.
To give an example, I will use a multimeter that has only one setting on the dial for
current, which is labeled with the letter A. I can set the dial here and my display
shows a value in DC current.
I can push the mode button to toggle to AC current measurements.
The settings that can be toggled may change from unit to unit, but are usually listed
next to or below the default setting.
. My next setting would be for resistance, which
is measured in Ohms and indicated by an Omega symbol from the Greek alphabet.
This setting can be used to check individual resistors or potentiometers.
I can place my test leads across the resistor to get a reading.
For checking a speed pot, I could use hook leads and measure across two ends of the speed
pot.
Next I will use the continuity setting which appears kind of like a sonar wave or a sound
wave such as in a computer’s volume control.
Devices should not have any powered applied when testing in order to make sure that the
test is accurate.
This can help determine if an electrical connection is made properly.
I can use this circuit board that has a new connection that had just been soldered in.
I will touch two points to see if the connection was made well.
If I get an OL or no reading, then I know that the connection was not mage or that the
two points are not electrically connected.
Diode testing is displayed by a diode symbol.
Testing a diode requires finding the anode and cathode of the diode and ensuring that
the diode disconnected from a power source.
I can then use the red probe on the anode and the black probe on the cathode.
There should be a voltage drop displayed and a numerical value on the display.
I will then reverse the probes and conduct the test again.
There should be no voltage drop and an OL should display.
This indicates the diode is working properly with voltage going in one direction and not
the other.
For more in-depth testing and understanding of digital multimeters, please check out our
other videos on G-TV.
Multimeters along with thousands of products and services are available at galco.com.
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