Multimeter

Table of Contents: 

What is a Multimeter? 

A multimeter is a test equipment device that can be used to measure, diagnose, or troubleshoot electrical circuits and components. This device is a combination of a voltmeter, ammeter, and ohmmeter as it can be used to measure voltage, resistance, and current, as well as other electrical values, for diagnosing and testing purposes. Multimeters can be used to carry out simple tests such as measuring battery voltage, or more complex tests, such as detecting faults in a circuit [1]. Multimeters can be used to diagnose a variety of electrical components found in motors, appliances, power supplies, and wiring systems [2]. 

Multimeters are comparable to oscilloscopes in terms of their main functions, but the key difference between the two is the amount of information conveyed to the user. A multimeter only numerically displays the measurements of various electrical values, whereas oscilloscopes are able to visually display waveforms, revealing the wave shape that includes its frequency and amplitude (voltage), in addition to the numerical value of the measurement [3]. 

Functions of a Multimeter

Multimeters are capable of collecting various readings depending on the model of multimeter and how advanced the specific model is. Most basic multimeters can measure voltage, current, and resistance, while also being able to check for continuity of the circuit. The continuity of a circuit describes the presence of a complete path for current flow around the specific circuit. More advanced models, which can be more expensive, are capable of measuring additional values, such as [1]; 

• • Capacitance (Farads) 
  • Inductance (Henrys) 
  • Conductance (Siemens)
  • Frequency (Hertz) 
  • Gain (Decibels) 
  • Temperature 

Accessories can also be added to more advanced multimeters for additional readings such as light levels and acidity/alkalinity. 

Types of Multimeters

There are two main types of multimeters that exist in industry, digital multimeters and analog multimeters. Both types of multimeter perform similar functions, but the key difference is in the way the information is displayed to the user and the accuracy of the devices themselves [1]. 

Analog Multimeters

An analog multimeter is a needle-based multimeter where the needle moves over a scale to indicate the measured values [1]. In an analog multimeter, a needle moves over a large scale with various electrical values (voltage, current, or resistance) and the user can read off these values based on the location of the needle over the scale [5]. Some downsides to analog multimeters are that they are usually not as accurate as digital multimeters and are hard to read accurately by the user due to the needle/dial moving over a complex scale. Since analog multimeters tend to have higher resistance, they make very good voltmeters as they can detect and display slow voltage changes, which can easily be followed by the slight movements of the needle. Analog multimeters are now becoming legacy devices, and are being rapidly replaced by digital multimeters [6]. 

Digital Multimeter

Digital multimeters are the most common type of multimeter currently in use. The key characteristic of this type of multimeter is the replacement of the moving needle and scale with a LCD screen that digitally outputs the readings [1]. This digital reading provides values which are easier to read when compared to the analog multimeter. The digital reading also has greater accuracy of the electrical values due to the screen having a greater resolution (number of digits displayed). Digital multimeters, like analog multimeters, have flexible test leads that are plugged into the multimeter that act as the conductor when a certain electrical component needs to be tested [9][10]. 

It should be noted that in both analog and digital multimeters, when measuring in the AC Mode (AC Voltage), the value shown is an RMS (root-mean squared) value, also called the "effective value" of the AC current or voltage [12]. This RMS AC voltage/current value represents the equivalent DC voltage or current of this value, which may be a bit inaccurate compared to the true AC value. The use of a RMS value while in the AC mode is to compensate for the the alternating nature of AC current or voltage [13]. 

Parts of a Multimeter 

A typical multimeter consists of four main components that help in testing various electrical components and display the information back to the user. Such components include [14]:

1. Display
2. Rotary range dial 
3. Main connection ports 
4. Probes/leads 

Display 

The display is usually a multi-digit LCD screen that is used to display the measurements being taken and also features a +/- indication. This display is replaced by the needle and scale combination on analog multimeters [9]. 

Rotary Range Dial 

This dial allows the user to select the desired measurement that needs to be made and the range that is required. These rotary range dials differ for each type of multimeter. It is typically good practice to select a maximum range that is above the anticipated value to prevent the multimeter from being overloaded [9].

It is important to ensure the correct measurement range is selected on the dial, based on the desired measurement being taken. Selecting an inappropriate measurement range on the dial, such as measuring voltage while leaving the dial in current mode can cause the multimeter to draw a lot of current from the circuit and melt the built-in fuse of the multimeter, or destroy the multimeter completely [15]. 

Main Connection Ports

These ports are where the flexible leads/probes are plugged into. Depending on the type of measurement being made, the leads will be plugged into different ports. The COM (common) is used with all measurements and is used for the black/negative leads. The voltage, current, resistance port is used for most measurements and is to be used with the positive/red lead. The other port found on the multimeter is for situations with high current measurements. This is used to prevent overloading the multimeter when testing certain components [9]. 

Probes/Leads 

These flexible leads have a pointed tip at one end to touch against the electrical component being measured, while the other end is plugged into the connection ports on the multimeter. It is important to plug the probes into the correct ports on the multimeter to prevent overloading the multimeter from high current, which can lead to a broken fuse or multimeter entirely [14]. 

How to Use a Multimeter?

Using a multimeter is quite simple if the user has knowledge on how to take voltage, current, and resistance measurements. The following steps outline how to setup and use a multimeter [9]: 

1. Turn on the multimeter and plug the leads into the correct connection ports based on the type of measurement being taken. Only two ports are needed to be in use at one time. 
2. Set the switch to the desired type of measurement and range that the measurement needs to be taken in.
3. Make sure the range is optimized for the best readings, so that the greatest number of significant digits can be displayed.
4. Touch the leads to the corresponding ends of the electrical device/component being measured.
5. Take the reading on the LCD display (or needle and scale for analog multimeters).

References

[1] J. Rodriguez. "What Is a Multimeter?" The Balance Small Business. 26-Nov-2018. [Online]. Available: https://www.thebalancesmb.com/multimeter-what-is-a-multimeter-844780. [Accessed: 05-April-2021].

[2] "What is a Digital Multimeter?" Fluke. 12-Jan-2021. [Online]. Available: https://www.fluke.com/en-ca/learn/blog/electrical/what-is-a-digital-multimeter. [Accessed: 05-April-2021].

[3] "Oscilloscope vs. Multimeter Comparison." Fluke. 08-Mar-2021. [Online]. Available: https://www.fluke.com/en-ca/learn/blog/oscilloscopes/oscilloscope-vs-multimeter#. [Accessed: 13-April-2021].

[4] "Digital Multimeters - Hand Held." Newark. [Online]. Available: https://canada.newark.com/duratool/d03124/digital-multimeter-hh-10a-600v/dp/21AH3208. [Accessed: 05-April-2021].

[5] "How to Use a Multimeter." Sparkfun. [Online]. Available: https://learn.sparkfun.com/tutorials/how-to-use-a-multimeter/all. [Accessed: 05-April-2021].

[6] "Analog Multimeters." The Electricity Forum. [Online]. Available: https://www.electricityforum.com/iep/electrical-test-equipment/analog-multimeters. [Accessed: 05-April-2021].

[7] "Analog Multimeter." AliExpress. [Online]. Available: https://tr.aliexpress.com/item/32895132282.html. [Accessed: 05-April-2021].

[8] "Analog Multimeter Reading." ShutterStock. [Online]. Available: https://www.shutterstock.com/video/clip-24149656-analog-multimeter-reading-basic-meters-usually-have. [Accessed: 05-April-2021].

[9] "What is a DMM, Digital Multimeter?" Electronics Notes. [Online]. Available: https://www.electronics-notes.com/articles/test-methods/meters/dmm-digital-multimeter.php. [Accessed: 06-April-2021].

[10] "How a Digital Multimeter Works." Electronics Notes. [Online]. Available: https://www.electronics-notes.com/articles/test-methods/meters/how-a-dmm-digital-multimeter-works.php. [Accessed: 08-April-2021].

[11] "Professional Digital Multimeter." Schniebel Trading. [Online]. Available: https://schniebel.com/UT-139E/en. [Accessed: 06-April-2021].

[12] "How an Analogue Multimeter Works." Electronics Notes. [Online]. Available: https://www.electronics-notes.com/articles/test-methods/meters/analogue-multimeter-how-does-it-work.php. [Accessed: 08-April-2021].

[13] "What's the Difference between RMS and "True" RMS?" Pass. 12-Oct-2021. [Online]. Available: https://www.tester.co.uk/blog/electrical/multimeter-jargon-busters-true-rms/. [Accessed: 13-April-2021].

[14] "How to Use a Multimeter?" DenGarden. [Online]. Available: https://dengarden.com/home-improvement/Using-a-Multimeter. [Accessed: 07-April-2021].

[15] "What will happen if we try to take a voltage reading by keeping it in current mode in a multimeter?" Physics StackExchange. [Online]. Available: https://physics.stackexchange.com/questions/574888/what-will-happen-if-we-try-to-take-a-voltage-reading-by-keeping-it-in-current-mo#. [Accessed: 13-April-2021].

Contributors: 

Faculty Advisors: Kim Pope, John Thistle, Vincent Gaudet, Michael Lenover (alumni), Allyson Giannikouris