What is a Digital Multimeter & How to Use One

A digital multimeter (DMM) is an electronic device that is used to measure various electrical properties, such as voltage (V), current (A), and resistance (in Ohms). Digital multimeters also display measurements on their digital screens, making it easy for users to read results accurately. In short, a DMM combines the functions of a voltmeter, an ammeter, and an ohmmeter into a single handy unit.

• Voltage is the difference in electrical potential between two points, expressed as the potential energy of an electric field to cause current flow through a conductor or circuit.
• Current is the active rate of electrical charge flow through a component or circuit, measured as it passes a designated point or region on the circuit (for most circuit types, this charge flow is typically carried by electrons moving through a wire).
• Resistance is a measurement of the extent to which the properties of a specific device or material limit the rate of electrical current flowing through it.

In New Zealand, these devices are also known as digital multitesters. All of these tools generally require a variety of probes and test leads to be plugged into them to transfer signals to and from the components, contacts, wires, or traces being tested.

What does a digital multimeter do? Multimeters can be used for a wide range of monitoring, detection, analysis, and troubleshooting applications. This will depend on what aspect and stage of electronic prototyping or troubleshooting you are concerned with and the specific details of the electrical circuit, component, or fault being tested.

In short, they can be used for any job requiring accurate readouts of device voltages and resistances as an easily measurable output value. Specific examples might include:

• Electrical testing of plug sockets and lighting setups
• During wiring installation
• General analysis and measurement of devices and components such as batteries, electric motors, and power supplies
• Fault-finding and troubleshooting of electronic circuits

The main parts of a standard digital multimeter typically consist of a:

• Display Screen: Shows the measurement readings and other information.
• Rotary Switch: Selects the measurement function (voltage, current, resistance, etc.) and range.
• Input Jacks: To connect the test probes to the meter. Different jacks are used for different measurement functions.
• Test Probes: To connect to the circuit or component being measured. They typically have red and black leads with pointed tips or alligator clips.

How To Use A Multimeter:

Using a digital multimeter is straightforward, but following these steps will ensure safe and accurate measurements:

1. Inspection: Before use, visually inspect the digital multimeter and the device under test (DUT) for any signs of physical damage that could compromise safety or accuracy.
2. Probe Connection: Connect the appropriate probes to the color-coded input jacks on the multimeter. The red probe is typically connected to the positive terminal, and the black probe to the negative terminal.
3. Mode Selection: Configure the digital multimeter settings to the desired mode (resistance, voltage, or current) and range using the rotary switch.
4. Functional Verification: Verify the functionality of your digital multimeter by testing it with a known voltage source, such as a battery. This confirms that the meter is working correctly.
5. Measurement: Use the probes to measure the desired electrical property by placing them on the appropriate test points of the DUT.
6. Safety Monitoring: While working, keep an eye on the digital multimeter's display screen for any safety warnings or overload indications.

Understanding the function and uses of digital multimeters is essential for effectively utilising this versatile tool in various electrical and electronic applications. It's important to note that the steps above cover the basics of how to use a digital multimeter, but users should always consult the model-specific instruction manual before operating a digital multimeter to ensure practices are safe. Additionally, there are numerous methods for using a DMM to give a meaningful readout on any circuit or component. However, it will largely depend on what you are measuring.

Common uses include:

• Device or circuit voltage measurement
• Component resistance measurements
• Measuring the current flowing through a circuit
• Measuring continuity on components such as switches, connections and fuses
• Testing diodes
• Measuring a capacitor's value
• Measuring the frequency of an AC signal
• Temperature measurement (provided that the particular multimeter has the correct input)

Each function will involve using slightly different methodologies, functions and settings on your digital multimeter.

You can use the image below as a generalised digital multimeter user guide to familiarise yourself with the tool’s basic settings, probes and functions:

Using a digital multimeter safely is essential for all work sites across New Zealand. As with all electrical test equipment, you should always ensure your multimeter is in proper working order and safe to use before taking measurements.

Safety checks include:

1. Ensure you are wearing the appropriate PPE
2. Perform a visual inspection, checking for any damage, cracks, and other potential hazards
3. Verify that the multimeter is operating as it should, using a proving unit or known voltage source
4. Monitor the instrument carefully during use in case warnings or irregularities are detected

Other important safety considerations include:

Fused vs Non-Fused Multimeter Test Leads

Fused test leads provide an additional level of protection to users. However, there are also some negatives to using fused test leads that you should keep in mind. For instance, a blown fuse may suggest that a measured circuit is dead when it is actually live. This can be addressed with safe working practices such as using a proving unit.

These leads can also introduce additional resistance into the test lead, potentially affecting reading accuracy for resistance, for example. It is recommended to carry out a risk assessment to identify whether fused or non-fused leads are the most suitable for a given application.

Built-In Fuses

Any multimeter that measures current must have an internal fuse to protect both the user and the meter from excessive currents. This is essential if the meter is connected to a live voltage source, where a short circuit will be applied. It is critical that such a fuse is replaced with another of the same specification to ensure ongoing protection against short circuits. Failure to do so could lead to significant injury.

Measurement Categories

It is important to note that levelled categories of digital multimeters are available for use in different locations, voltages and circuit types. You will need to choose the appropriate category for your specific application.

• Measurement Category I: Best used for testing circuits that are not directly connected to the mains or specially-protected internal mains-derived circuits.
• Measurement Category II: Best used for testing circuits that are directly connected to low-voltage installations. Examples include domestic appliances and smaller, portable tools.
• Measurement Category III: Best used for testing circuits involved with building installation, such as wiring, circuit breakers, and distribution boards, as well as industrial equipment.
• Measurement Category IV: Best used for testing at the source of low-voltage installations, including electricity meters, ripple control units, and overcurrent protection devices.

In terms of knowing how to read digital multimeters properly, you will need to be familiar with the basic symbols found on standard electronic schematics to fully understand all of the various output readings from your DMM.

Digital Multimeter How-to Guide

Digital multimeters (DMMs) are handheld tools that can measure capacitance, voltage, electrical current, and resistance using diode and continuity checks.

Watch our handy video to find out more!

As covered in the video above, this multimeter can measure both current and voltage. When measuring current, it's important to exercise caution, as the multimeter becomes part of the circuit, and there's a chance of shorting it if it is not used correctly.

This multimeter is also auto-ranging for voltage measurements, meaning it automatically selects the appropriate measurement range. It also features a resettable fuse for protection, and the probes are rated to 10 amps. For added convenience, it has an auto-shutoff feature and a built-in flashlight. Importantly, it is CAT 4 rated, meaning it can be safely used to measure up to 600V.

When testing for continuity, you would touch the probes together. If the reading is zero, it indicates a closed circuit, meaning there is a continuous path for the current to flow. If the reading is not zero, it indicates an open circuit, meaning there is a break in the circuit and current cannot flow.

Explore RS Pro Digital Multimeters

Take a look at this handy video for an in-depth look at one of our RS Pro digital multimeters. With a wide range of features, multiple functions, and powerful testing capabilities, the benefits of choosing an RS Pro digital meter are clear to see.

Watch the video to learn more, or click below to browse our full range of RS Pro digital multimeters.

Digital multimeters are useful tools that are used daily across a broad spectrum of professional scenarios. They are widely available in various models and form factors.

Many modern DMMs also provide a range of enhanced features and modes to cover an even broader array of electronic tasks. These include:

• The ability to switch between AC and DC measuring modes
• Diode and continuity testing
• Advanced models may also include the ability to test for capacitance and inductance

Multimeters can be designed either as highly portable handheld devices or built for semi-permanent installation on a work surface. The characteristics of each are as follows:

Handheld Multimeters:

• Ideal for fieldwork or accessing confined spaces
• May be less accurate than fixed models due to physical constraints limiting measuring components
• Typically can only take one measurement at a time

Benchtop Multimeters:

• Intended for stationary use or on a workbench in production test applications
• Offers greater accuracy than handheld models
• May have the ability to be remote-controlled
• Can take multiple measurements at once

Spotlight: True-RMS Digital Multimeters

A true-RMS (TRMS) digital multimeter is a specific type of multimeter. RMS stands for root mean square, and these devices are often preferred to their standard counterparts. This is because true-RMS multimeters are the only type that can accurately measure both sinusoidal and non-sinusoidal AC waveforms.

Key Information:

• True-RMS devices accurately measure both sinusoidal and non-sinusoidal AC waveforms by calculating the equivalent DC current value of an AC waveform. This leads to a high degree of accuracy, unlike standard averaging multimeters, which can lose up to 40% accuracy when attempting to measure non-sinusoidal waveforms.
• The prevalence of non-sinusoidal waves in circuits has increased significantly over recent years. This means that true-RMS has become a much greater necessity, and these types of multimeters have become more widely used.
• Some examples where measuring true-RMS could be useful include electronic ballasts, HVAC systems, variable-speed motor drives, and solid-state environments, where non-sinusoidal waveforms are common.

Analogue multimeters perform many of the same functions as their digital counterparts but use traditional dials to zero in on voltage, current and resistance settings. While you can still buy analogue multimeters, you are more likely to use digital nowadays. As a result, analogue multimeters tend to be much less widely available than modern digital versions, which are generally more efficient, accurate and cost-effective.

To effectively use either type of multimeter, it is important to know how a digital and analogue multimeter works. You must also understand what a multimeter can measure and how to interpret the readings correctly, whether it's displayed on a digital screen or an analogue dial.

Analogue meters can be useful on rapidly fluctuating circuits as the needle can be observed more easily than a rapidly changing digital display. In addition, analogue meters tend to have a lower input impedance (DMMs are typically 10 Megohms), which is useful for measuring voltages in certain types of circuits. However, digital multimeters help to address these needs. Some offer an analogue bar graph to simulate an analogue dial. Certain models also include a low impedance (low Z) mode to reduce the possibility of false readings due to ghost voltages and improve the accuracy of measurements.