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 new DMMs also provide a range of enhanced features and modes to cover an even broader array of electronics tasks. This also allows them 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.
Various types might also offer additional settings for diode and continuity test functions, often indicating the status of certain readings via an audible alarm. Depending on the exact model, further optional modes and advanced features 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 fieldwork 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 will 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. Bench multimeters typically also offer the ability to be remote-controlled and to make large numbers of measurements per second. These functions are often used in production test applications.
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.
RMS devices achieve this by calculating the equivalent DC current value of an AC waveform. Therefore, these sophisticated instruments can measure both types of waveforms to a high degree of accuracy. To put this into perspective, standard averaging multimeters may lose up to 40% accuracy when attempting to measure non-sinusoidal waveforms.
The potential for 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.