Cool Tools: Multimeters

A range of multiple functions combined in one device gives the multimeter its name and makes it an essential test instrument for both electrical and integrated systems work.

Basic multimeters work as a voltmeter, ammeter and ohmmeter, easily switching from one function to another. Other capabilities and features are added as models progress to specialty and advanced functions, ensuring technicians can find exactly the right instrument for their needs.

With other testers having some multimeter capabilities, is demand decreasing for the true multimeter? Absolutely not, said André Rebelo, global communications manager, Extech Instruments, a division of FLIR Commercial Systems.

“Far from it,” he said. “At the end of the day, the digital multimeter [DMM] remains the undisputed utility player in the electrical tool bag. In point of fact, a range of features and functions, like data recording, wireless data streaming, and insulation resistance testing, are being added to DMMs to expand their versatility, putting more ‘multi’ in the multimeter.”

Representatives of four established multimeter suppliers share their thoughts on the multimeters available today.

John Olobri, AEMC Instruments director of sales and marketing, said: “For electrical applications, basic multimeters measure [alternating current] AC and [direct current] DC volts and current, resistance, continuity, and diode testing. Some meters are also available with measurement ranges for capacitance, temperature, phase rotation and power.

“Significant changes include the addition of more functions, such as wireless communications, data logging, power measurements and infrared temperature measurements. Improved materials and case over-molding have improved the ruggedness, and accuracies have improved to the 0.1 to 0.3 percent range. Multimeters used primarily for electrical measurements also can be used for testing low voltages of security, alarm and control systems. Continued demand for analog models is based more on preference than need. Digital meters are far more easy to use in interpreting accurate readings. Analog meters provide a better sense of rate of change,” Olobri said.

Extech’s André Rebelo said: “When it comes to diagnostic work, the digital multimeter is a must-have. They are still called voltmeters or volt ohmmeters (VOM) by many users, but they are the same.

“Besides the essential need to measure voltage (V DC and V AC) and current (amperes), multimeter users can reasonably expect a basic DMM to offer a number of capabilities. A ‘sufficient’ set of essential functions to look for include resistance (ohms), duty cycle, capacitance (nF/pF), and frequency (hertz). Open circuit voltage for diode checks and continuity testing also is indispensable.

“Temperature is often a valuable complementary indicator to electrical conditions, and meters can measure temps via Type K (thermistor) probes. For added safety, a built-in, noncontact infrared thermometer or pyrometer helps take some DMMs into another category of multifunctionality altogether.

“There have been a number of improvements in recent years that have expanded the safety and usefulness of DMMs. For example, wireless data streaming permits readings to be transmitted to a remote location away from energized equipment or dangerous machinery. Today’s multimeters can also have a big impact on best practices in a plant’s electrical predictive maintenance. Think about insulation resistance testing. It’s often performed with a megohmmeter—a tool that isn’t always on hand.

“DMMs also are used by installers of security, alarm and control systems. From low-voltage systems ranging from undercabinet LED, xenon or halogen lighting to web- and app-enabled home automation systems, to outside surveillance cameras, today’s DMMs are useful for testing during installation and for troubleshooting to identify problems, such as continuity and grounding, as well as factors related to deterioration from exposure to harsh year-round weather.

“Digital multimeters have effectively taken over the market for electrical contractors. They generally are more accurate with more precise readings, require less manual calculation and decoding by the user, and tolerate more operator errors without damage or danger, and without fragile mechanical components; they are less susceptible to being damaged or decalibrated from accidental drops. They also do not take any parasitic energy from the circuit or device under test,” Rebelo said.

Duane Smith, Fluke Corp. digital multimeter product specialist, said: “A DMM is simply an electronic tape measure for making electrical measurements. It may have any number of special features, but mainly a DMM measures volts, ohms, amperes, and a continuity beeper, followed by FHz, diode test, and min/max. Most important is that the meter be appropriately safety-rated for the electrical environment. Use only meters rated CAT III, 600V and above.

“The biggest single change in DMM capabilities has been wireless communications of live and recorded electrical and temperature measurements between the DMM readout and the point of connection, between multiple DMMs and/or laptops, and to the cloud apps.

“Many multimeters can be used for both medium and low-voltage applications. The key is to check the meter resolution (how many digits/how fine a measurement) and range. By knowing the resolution, you can determine if it is possible to see a small change in the measured signal. For example, if the DMM has a resolution of 1 mV (1/1,000 of a volt) on the 4V range, it is possible to see a change of 1 mV while reading 1V. The most common measurements taken for security installation, commissioning and service are voltage, current, resistance and ground. Most Class 2 and 3 low-voltage systems are 12 or 24V DC, which means meters rated to 10V on the low end can be used for the majority of security, alarm and control applications. We see very little need today for analog meters,” Smith said.

Patrick Elliott, Ideal Industries field sales engineer, said: “Min/max and peak are useful features. The term multimeter has also been used to describe other meter devices, but DMM most often implies the measurements of the meter go through some type of signal conditioner to a microchip, which converts the analog measurements to a digital output, which is read on an LED or LCD display.

“Most DMMs with high impedance of 10 meg-ohms that have 4,000- or 6,000-count displays with a 40V or 60V range should work fine for testing security and alarm systems, and this covers almost 90 percent of common DMMs on the market today. Almost all digital multimeters used today are auto-ranging from 400 mV with 0.1 mV resolution to 600V.

“There have been significant changes to DMMs in safety and operation. One of the most common mistakes made by users of a multimeter is to have the test leads in the wrong port. This can lead to extreme hazards not just to the meter but, in some cases, [could] lead to an arc fault or, worse, an arc blast. Besides improved input protection components, like high-energy fuses, some meters will provide an audible or display warning of incorrect operation.

“In most cases, digital is king with multimeters, but there are a few areas where analog instruments are useful. DMMs normally have very high input impedance where analogs have low to very low impedance. In some cases, like the presence of ghost voltage, a low impedance meter is preferable. Another common issue with digital meters that are battery-powered is that the user ignores low-battery warnings, and the instrument becomes erratic. Most analog testers are passive and derive their energy for the source,” Elliott said.

Ian Bensted, Megger applications engineer, said: “For basic electrical work, ampere, volt and ohm ranges would be required as standard; however, additional frequency and temperature ranges may prove to be useful. In addition, a data hold should be considered as a very useful requirement.

“Modern multimeters have the capacity to measure voltages in both electrical installations and ultra low-voltage systems, such as security, alarm and control systems. There are now a number of clamp meters and voltage testers, which feature certain multimeter functions like continuity, ohms and frequency, but generally, these additional ranges have reduced specifications, which are sometimes useful but lack the full range provided by a true multimeter.

“A large number of multimeters now have a CAT IV safety rating, which allows the user to make measurements in previously ‘DMM unsafe’ areas, such as at the input of an electrical installation. A Trms feature now means accurate readings can be taken on circuits with a distorted sine wave. A number of DMMs now have internal storage of test data.

“Now that the digital age is firmly with us, the need for an analog multimeter seems unwarranted. However, conversations with traditional radar or radio personnel reveal life still breathes in the analog meter world. Both of these industries require the smooth operation of the analog movement to give varying readings. The jerkiness of the digital display does not lend itself to these applications,” Bensted said.

About the Author

Jeff Griffin

Freelance Writer
Jeff Griffin, Oklahoma City, is a construction journalist specializing in the electrical, telecommunications and underground utility construction industries. Contact him at .

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