How To Use A Multimeter

A very handy tool to have in your electronics kit is a Digital Multimeter. Sometimes called a dmm, multimeter or just meter, there are many applications for using this in your maker classroom and workshop.

You can use a multimeter to identify dead or good batteries, find the value of a resistor, measure the amperage in a circuit, determine voltage and polarity, test for continuity and more.

Concepts
Use of tools
Testing for voltage, amperage, resistance

Supplies
Carbon resistors
Potentiometer
A circuit with battery, wire and load such as an LED or motor
Keys or other metallic objects
Bottle or other plastic and glass objects
Wire, stranded or solid core
Batteries of various types
Paper and pencil

Tools
Digital multimeters
Wire strippers or cutters

Time frame
The first parts of this can be covered in well under an hour, but this is a very useful tool with many applications. You will want to review its’ usage through application during projects.

Mastery objective
Students and participants will know how to properly set a digital multimeter so that they can use it to measure for voltage, resistance, amperage and conductivity.

Process
Assemble your tools and supplies.
Have a paper to keep track of the information that the meter helps you find.

Know your meter
There are a few types of meters, manual and Auto ranging. Most modern meters have digital readouts, but older meters have an analog pointer. Your meter should be fused. If the meter stops working, you either blew the fuse or the battery is dead. Many meters have auto turnoff features to save battery life.

With a manual meter , you have a knob with lots of settings, decide the approximate value that you are testing for, then put the indicator to the setting one higher than what you think it will be. If you are too high or too low, it will give an out of range reading, such as 1.

An autoranging meter will find the value for the variable you are testing for. You set it to the variable and put it on a circuit, it will find the value for you. There are only a few settings on an autoranging meter.

Testing for voltage
Volts DC indicated by a bar with three dots below it. This is for measuring direct current voltage. Put the test probes in parallel in the circuit, touch two points on the circuit and it will measure the value between them.

Volts AC indicated by a ~ sine wave symbol. Alternating current voltage. Put the test probes in parallel in the circuit, touch two points on the circuit and it will measure the value between them. Current switches direction 60 times per second North America 50 times/sec in Europe.

What is the resistance?
Resistance indicated by Greek omega symbol. Resistance is measured in Ohms, can be followed by K – x1000 KiloOhms, M – x10,000 MegaOhms. Put the test probes in parallel in the circuit, touch two points on the circuit and it will measure the value between them.

Testing for Amperage
Amperage indicated as A or mA. Amperage is measured in amps or milliamps. Put the test probes in series, disconnect the circuit, bridge the gap with the probes of the meter. Make amperage readings for brief times only. If you leave it connected for longer, you may blow the fuse. If you are measuring a higher amp circuit, you will have to move the red probe from the regular port to the 10a or 20a port. Switch it back when you want to measure volts or amps.

Conductor or insulator?
Continuity indicated as a point with several arcs emanating from it. Put the test probes in parallel with the circuit. The meter will beep to indicate a complete/closed circuit between the two points of the probes.

More:

• Electronic Test Equipment from MAKE, Volume 10
• Multimeter Tutorial – Make: Video Podcast
• Multimeter Tutorial – Make: PDF Podcast
• Free classroom electricity posters
• How-To: CD drive scavenging for parts
• http://www.doctronics.co.uk/meter.htm
• How-To: Free DIY battery holders
• How-To: Quick, cheap soldering stand
• http://www.bobvila.com/FixItClub/Task/Repairing/FIG_Multimeter.html