Choosing the Right Multimeter

Chauvin Arnoux analog multimeter

There are two main types of multimeters: analog multimeters, which utilize older technology but are still popular among professionals, and more modern digital multimeters.

Analog multimeters 

These have a dial with a needle and various graduated scales depending on the different electrical values measured by the device and the measurement ranges it allows you to select. They operate like galvanometers, meaning that the movement of the needle on the dial is caused by the current flowing through the device.

They are accurate and reliable instruments, but reading the measurements requires some practice to avoid errors such as parallax error (which occurs when the eye is positioned incorrectly) or reading the measurement on the wrong scale.

Digital multimeters

These use an analog-to-digital converter and have a digital display that directly shows the measurement value. Compared to analog multimeters, measurement readings are more accurate and there is no risk of parallax error or reading on the wrong scale. On the other hand, they make it more difficult to measure values that fluctuate constantly because the analog-to-digital converter reacts more slowly to fluctuations than an analog needle.

As well as being easier to use, digital multimeters require less frequent calibration, are more shock resistant, and can be waterproof and dustproof.

General purpose multimeters

These are intended for use by the general public or simple applications. These inexpensive multimeters can be used to measure voltage, current, and resistance on simple electrical circuits, as long as the aim is not to obtain very precise measurements but simply an approximate value.

Professional multimeters are more resistant and more precise:

Professional handheld multimeters

Lightweight and compact, these offer great freedom of movement to take measurements and detect and solve problems in the field. They are used by professionals in various fields, including electricians.

Gossen Metrawatt handheld multimeters

Benchtop multimeters

These are mainly used by engineers to take precise measurements on electrical or electronic circuits. They offer advanced measurement functions.

B&K Precision benchtop multimeter

The IEC 61010 standard defines overvoltage categories (also known as electrical safety categories) for low-voltage installations (< 1000 V). These categories classify the different parts of electrical circuits according to their risk of overvoltage and consequent level of danger.

There are four overvoltage categories:

• CAT I: Electronic devices
• CAT II: Equipment connected to single-phase outlets, such as household appliances
• CAT III: Three-phase distribution and single-phase commercial lighting
• CAT IV: Power lines

Electrical measuring devices such as multimeters are classified according to the overvoltage category they are intended for, which corresponds to the level of protection they offer.
For example, a multimeter designed for overvoltage CAT II cannot be used safely on a CAT III electrical installation.

The maximum voltage level is also specified for each category. For example, a CAT III 600 V multimeter can be safely used in a CAT III zone with a maximum voltage of 600 V. However, it is not safe to use if the voltage is higher than 600 V, even if in a CAT III-rated part of the installation.

Safety ratings and associated voltages are clearly indicated on the multimeter.

There are therefore CAT I multimeters, CAT II multimeters, CAT III multimeters, and CAT IV multimeters.

Safety ratings marked on a multimeter

A multimeter combines the functions of several electrical measuring instruments in a single device. Multimeters generally measure voltage (voltmeter), current (ammeter), and electrical resistance (ohmmeter). However, there are models offered by manufacturers that incorporate more measurement functions to meet the needs of different professionals.

Multimeter with Metrel thermal imaging camera

A multimeter can also provide other electrical measurements, such as:

• Diode tests
• Continuity tests
• Capacitance measurements
• Frequency measurements
  

It can also have other functions, such as temperature measurement, either by contact, with an external probe, or without contact, by infrared or via a thermal imaging camera.

When buying a multimeter, make sure you choose a model that integrates all the measurement functions you need for your professional activity.

After choosing which type of multimeter you need, it is important to pay attention to the following technical specifications:

RMS or True-RMS: This is an important difference between low-cost multimeters and professional multimeters. When measuring an alternating current, the multimeter displays an “effective” value. RMS multimeters calculate the effective value on the assumption that the signal is perfectly sinusoidal (if it is not, the value displayed will therefore be incorrect). True-RMS multimeters, on the other hand, are more expensive, but they measure the true effective value of the signal. They therefore measure AC signals more accurately.

Accuracy: This is the difference between the actual value measured and the value displayed by the multimeter, expressed as a percentage of the measurement range. The lower this percentage, the more accurate the device. Note that the more accurate the device, the more expensive it will be. There’s no need to choose an extremely accurate multimeter for applications where accuracy isn’t important.

Resolution: This is the smallest increment that the multimeter can display. On a digital screen, this would be the last digit displayed. Like accuracy, the lower the resolution, the better the multimeter.

Measuring range: This is the maximum value that the multimeter is capable of measuring for each electrical measure.