A Complete Guide to Digital Multimeters

What is a digital multimeter?

Digital multimeters - often shortened to DMMs - collectively form a range of versatile and incredibly helpful tools, designed for measuring and displaying various important parameters relating to electronic circuitry.
This will typically include voltage (V), current (as an amperage value, often shortened to amps or A), and resistance (in ohms). 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

You’ll sometimes see one of these gadgets referred to as digital multitester, which in this context is essentially the same thing. All of these tools generally require a variety of probes and test leads to be plugged into them, in order to transfer signals to and from the components, contacts, wires or traces being tested.

Digital multimeter uses and functions

As you might imagine, you can use a multimeter for a huge range of monitoring, detection, analysis and troubleshooting applications, depending on what aspect and stage of electronic prototyping or debugging you’re concerned with, and the specific details of the circuit, component or fault you’re testing.

Thus, in answer to the question ‘what is a digital multimeter used for?’, the simplest response would be ‘any job requiring accurate readouts of device voltages and resistances as an easily measurable output value’. Specific everyday examples might include:

• Electrical testing of plug sockets and lighting setups
• During home renovations and wiring installation
• When conducting device safety tests in the workplace
• General analysis, measurement, debugging and troubleshooting of electronic circuits, devices and components, such as

1. Batteries
2. Household wiring
3. Electric motors
4. Power supplies

How to use a digital multimeter safely

There are numerous different methods for using a DMM to give a meaningful readout on a given type of circuit or component. Precisely how to use a multimeter properly in any specific scenario will depend largely on what it is you’re trying to measure.

Common tasks you might need to carry out include:

• Measuring device or circuit voltage
• Measuring a component’s resistance
• Measuring the current flowing through a circuit
• Measuring continuity - i.e. the presence of a complete and unobstructed path for current flow - on various types of components such as switches, connections and fuses
• Testing diodes

Each of these functions will involve using slightly different methodologies, functions and settings on your digital multimeter. By means of a brief product overview, you can use the image below as a generalised digital multimeter user guide in familiarising yourself with the tool’s basic settings, components and functions:

How to read a digital multimeter

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

Different types of digital multimeters available

Digital multimeters are extremely useful tools, used daily across a broad spectrum of both professional and hobbyist scenarios, and are widely available in various models and form factors.

A majority of the DMM models available on today’s market also provide a range of enhanced features and modes to cover an even broader array of electronics tasks, and to offer full compatibility with a greater number of electrical devices and components. Importantly, the ability to switch between AC and DC current measuring capabilities is largely standard these days. (AC current flows from almost all household sockets, and to some larger appliances, while most common and smaller household device types - as well as batteries, electric vehicles and mobile phones - tend to run on DC current.)

Various brands might also offer additional settings for continuity and diode test functions, often indicating the status of certain readings via an audible alarm. Depending on the exact model you’re considering buying, further optional modes and advanced features you may wish to consider might include the ability to test for capacitance and inductance on relevant electrical components.

Multimeters can be designed either as highly portable handheld devices, ideal for field work and for accessing harder-to-reach circuits and machinery, or else built for semi-permanent installation on a work surface.

The latter type, known as bench meters or bench testers, tend to be bulkier and less easy to move around - however, they’ll typically offer a greater degree of accuracy and detail in their measurements and digital readout displays than their more lightweight handheld counterparts. The main difference between handheld and bench-top models tends to be in their maximum achievable accuracy: broadly speaking, the smaller a device is, the less sensitive (and therefore pinpoint accurate) it will be overall.

It’s important to note that various levelled categories of digital multimeters are available for use on different types of devices and voltages/currents. Depending on the specific application you need a multimeter for, you’ll need to ensure you’re shopping in one of the following general categories:

Types of digital multimeters available

Type of digital multimeter	Best used for
Category I	Testing of general household electronic devices/circuits, and smaller items of electrical equipment (chiefly specially protected secondary circuits)
Category II	Testing larger appliances and domestic loads (i.e. local-level electrical distribution, for example from a standard wall outlet or a typical plug-in load)
Category III	Testing industrial circuits, typically in the small-to-medium size range (hard-wired equipment in fixed installations, distribution boards and circuit breakers)
Category IV	Testing of more heavy-duty circuits and power sources, such as electrical mains and power lines, key electrical components in commercial areas, and domestic mains feeds (origin of installation or utility level measurements, e.g. on primary overcurrent protection devices and ripple control units)

What’s the best digital multimeter?

The best digital multimeter to buy in terms of value, functions and features will vary from customer to customer - in most cases, it will depend largely on what it is you need the unit to measure, and in what sorts of applications and environments.

Some popular subcategories of DMM for both professional and hobbyist buyers include:

What is the difference between analog and digital multimeters?

While you can still buy analogue multimeters - which perform many of the same sorts of functions, but using traditional dials to zero in on voltage, current and resistance settings - they're seen as somewhat primitive these days. As a result, they tend to be much less widely available than modern digital versions, which are generally more efficient, accurate and cost-effective in most day-to-day scenarios.