Five important criteria when choosing a digital multimeter
May 15, 2019 - Working with electricity can always be dangerous. When you’re choosing a handheld digital multimeter (DMM) for maintenance and troubleshooting purposes, you’ll want to be sure to use a device that has been properly tested to withstand hazardous working environments—but it can be difficult to sort through all of the relevant specifications to determine the best tool for the job(s).
The following are five key points to consider when selecting a DMM:
1. The category rating (CAT) for your environment
There is a common misconception that if choose a DMM with a high enough voltage rating, you will be covered in terms of safety. However, the voltage rating does not tell the full story.
A multimeter, after all, may be subjected to much higher voltage than the user thought was being measured, due to a high voltage spike or transient that hits the DMM input without any warning. Your safety depends on the corresponding margin built into your meter—which in turn is based on several specifications beyond the voltage rating.
The International Electrotechnical Commission (IEC) publishes international standards for all electrical, electronic and related technologies, including safety standards in the measurement category, which are the most important with regard to DMMs.
You should make sure any DMM you consider carries the IEC’s category rating (CAT)—which is typically displayed near the multimeter’s input jacks—that is most appropriate for the electrical environment in which you will be using it. Multimeters that are not CAT-rated, on the other hand, should never be used in high-energy, multi-phase electrical work environments. Also, be sure the test leads you use with the meter carry an equal or greater CAT rating.
A CAT II overvoltage rating corresponds to utilization points, including socket outlets and receptacles. CAT III is for the distribution part of the low-voltage mains installation, including commercial lighting. And CAT IV is suitable for the building's low-voltage mains installation (utility connection) and any outdoor conductors.
2. The ‘true’ voltage for the environment
It is also important to make sure your meter has the appropriate voltage rating for the electrical environment in which you will use it.
A higher voltage rating denotes a higher transient-withstand rating. This means the DMM’s input circuitry has been specifically designed to withstand voltage transients commonly found in the given environment, without harming the user.
Indeed, both the CAT rating and the voltage rating should be considered in conjunction with each other. A CAT III 1,000-V rated meter offers superior protection to a CAT III 600-V rated meter, for example, but a CAT II 1,000-V rated meter is not superior to a CAT III 600-V rated meter.
So, when you are looking to replace your multimeter, start your research by analyzing the worst-case working environment for your job and choosing the measurement category for that environment. Then choose a DMM rated for that measurement category, with the highest voltage rating you will need within that category.
3. The degree of ingress protection
If you work outdoors in harsh, wet and/or dusty environments, you will of course need a water- and dust-resistant multimeter.
IEC 60529, Degrees of Protection Provided By Enclosures, defines standards for both water and dust resistance in terms of levels of ‘ingress protection’ (IP) from solids and liquids. Each IP rating comprises two digits.
The first number specifies the size of excluded objects, such that zero indicates no protection, while six indicates the enclosure is dustproof.
The second number specifies the level of protection against water, with zero again indicating no protection and seven representing full protection against continuous, 30-minute immersion in 1-m deep water.
So, the highest possible rating for a DMM is IP67, which means testing shows it is dustproof and will withstand immersion in water to a depth of 1 m for up to 30 minutes.
4. How rugged your meter needs to be
No matter how careful you may be, your DMM is still going to be subjected to rough and tough conditions on a daily basis. So look for a solid, well-built instrument that is free of obvious defects and built to withstand years of use.
The most commonly accepted measurement for ‘ruggedness’ is in IEC 61010, Safety Requirements for Electrical Equipment for Measurement, Control and Laboratory Use. It specifies a product must be able to survive a 1-m drop, at both its highest and lowest specified operating temperatures. (If you’ve ever seen what happens to a multimeter that doesn’t meet that requirement after it falls on a concrete floor, you know how important that specification is!)
5. Independent testing
Look for the symbol and listing number of an independent testing lab, such as CSA, UL or RCM. That symbol can only be used if the product has successfully completed testing to the agency’s standards, which in turn are based on national and/or international standards. UL 61010-1, for example, is based on IEC/EN 61010-1.
Don’t trust multimeters that haven’t been independently tested.
Sean Silvey is a product and application specialist for Fluke, which manufactures electrical test and measurement tools, including multimeters, clamp meters and insulation, earth ground and installation testers. For more information, visit www.fluke.com/en-ca.
This article originally appeared in the April 2019 issue of Electrical Business magazine.
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