Cool Tools: Multimeters
Published: December 2010
Multimeters have been described as electronic tape measures for taking electrical measurements. Digital multimeter (DMM) instruments available today may include a few or many special features, but their basic purpose is to measure volts, ohms and amperes.
The trend over the past few years is to add functions and capabilities to testing instruments, raising the question: have other multifunction instruments replaced the need for multimeters? No, say most multimeter manufacturers.
By their nature, multimeters are general purpose and designed to cover a wide range of potential measurement situations, said Dan Wright, multimeter marketing communications manager for Fluke Corp. But taking a basic tester and adding multiple functions rarely produces the same results as a DMM.
In a highly digital world, analog -multimeters remain in use. There are electricians who used analog meters as apprentices, and still are comfortable with them. Analog meters provide a more graphic “feel” to the measurement being made, said UEi’s David Wheaton. Modern DMMs include an analog bar graph to represent the quick changes that, in the past, only had been available on an analog meter. However, the update rate of this bar graph must be quick enough to replace the information sometimes only available with an analog meter, he added.
An analog meter is more of a preference than need. Digital meters are easier to use in interpreting accurate readings. Analog meters can provide a good sense of the rate of change.
The one key application where an analog meter makes sense for a professional is where cold temperatures may affect the performance of the liquid crystal display of a digital meter, said Extech’s Andre Rebelo. Refrigeration-intensive environments such as cold-chain warehouse and logistical centers come to mind. Wintry outdoor settings may also qualify but analog meters without a CAT IV rating would jeopardize the user’s safety.
“Analog tools are really only used now when supporting legacy electrical systems or products,” Fluke’s Duane Smith said. “Even then, there are serious concerns regarding CAT rating and fusing for transient protection. Otherwise, analog tools have variable input impedance, which is not necessarily compatible with an increasing number of modern circuits and systems.”—J.G.
“Electrical testers tend to focus on the task for which they were originally designed,” Wright said. “Adding specialized features can help create a dedicated, special-use tester but rarely produces a compromise-free, versatile multimeter.”
Below, manufacturer representatives describe current multimeter trends.
John P. Olobri, AEMC Instruments (www.aemc.com) director of sales and marketing, said: “Users of multimeters want them to provide measuring ranges for AC and DC volts, AC and DC current, resistance, continuity, and diode testing. Accuracies have improved to the 0.1 to 0.3 percent range. Some meters also can measure ranges for capacitance, temperature, phase rotation and power.
“Many meters today have added functions, such as wireless communications, data logging, power measurements and infrared temperature measurements.
Improved materials and case over-molding has enhanced the ruggedness.
“The major difference between a true multimeter and a clamp meter is the integral current-measuring probe on the clamp meter. Over the last few years, the measurement functions of both have evolved.”
Extech Instruments (www.extech.com/instruments), Andre Rebelo, global communications manager, said: “Probably the most innovative new feature among multimeters is wireless data transmission. Indeed, DMMs have entered the world of wireless. DMMs available now can wirelessly transmit real-time or data-logged readings to a laptop or PC, with a 30-foot range—consistent with prevailing Bluetooth standards. Beyond remote monitoring of readings, this is also useful for analysis, trending and archiving.
“Voltage and current testing remain the key testing factors, but DMMs today come with a number of convenient data functions that expand their ability to measure by also capturing or calculating key values during testing. For example, one-button access to minimum and maximum values can help identify problems. An averaging function can help deliver a big-picture perspective. Hold, relative value and peak-hold functions are very useful diagnostic tools to capture instances that fall out of the normal range.
“These days, less and less sets clamp meters apart from DMMs. One key differentiator is that accuracy is generally better on DMMs, which rely solely on contact measurements using test leads, whereas the advantage of noncontact current measurements done by a clamp meter may trade off some accuracy that is not essential for certain tasks.”
Klein Enters the Tester Market
A recent trend among tool manufacturers is to add product lines that are a departure from their established market niche.
A good example is Klein Tools’ (www.kleintools.com) recent introduction of a line of testing equipment, which includes two digital multimeters.
Bruce Kuhn, Klein product manager, said Klein research found most electricians are not looking for multimeters that do more than measure voltage, resistance and continuity; that meet CAT IV safety standards; and that have exceptional input protection.
“It is not so much about how many things a meter does,” Kuhn said. “It is more about how well it can do the few items it needs to do.”
Beyond capabilities, Kuhn said Klein found users are looking for lighted displays, easy-to-read digits, low-impedance settings, hold buttons and other convenience features.
“Ease of use and the ability to change settings while wearing gloves are also important to users,” Kuhn said. “The meter needs to survive the tough environment that the average worker will be in every day.
inally, in this tough economy, an affordable meter is very important.”
Taking these factors in consideration, Klein Tools set out to create an affordable meter with the features that matter most to the electrician.
“The MM1000 and MM2000 meters offer 1,000V measurements, CAT IV safety ratings, large lighted displays, high energy fuses and a durable rubber boot. The MM2000 also features true RMS readings and a low-impedance setting.” —J.G.
Fluke Corp. (www.fluke.com), Duane Smith, digital multimeter support engineer, said: “The wireless display is the single biggest advancement in the last two years, bar none. Second is the advancement in on-site logging and graphing. Overall, advancement continues every year in accuracy, durability, safety and ease of use.
“DMM wireless display allows the user to connect to a measurement point, disconnect the display and move as far as 30 feet away while taking live readings. Now the user can connect to a test point that is inside a safety lockout door, close that door, and view readings while operating the controls outside that door. Other applications include situations where one technician was required to work in a tight cabinet or suspended ceiling, while shouting out readings to an assistant that was operating controls and jotting down numbers. This new DMM feature allows one man to perform two-person jobs more safely and more accurately.
“The newest generation of clamp meters offers many advanced functions, but even these advanced clamps don’t offer full ohms ranges or diode test, they’re still not as scalable, and they lack the measurement range and accuracy that multimeters offer.”
Megger (www.megger.com), Jeff Jowett, senior applications engineer, said: “Safety and durability are prime advances in new multimeters. A large number of multimeters are now used in on-site applications, and demand is for a rugged digital CAT IV TRMS multimeter where great accuracy is not paramount. The CAT IV rating provides a high safety specification for high-voltage testing, while the need for a sensitive instrument for precision work can still be met.
“In the modern electronic servicing world, the use of large-scale integrated circuits has nudged most multimeters into the shadows, so a number of instruments have been redeveloped for more harsh environments. While tough digital units are now found in mines and on oilrigs, analog and high-accuracy meters still have their place in different markets.
“The trend is for testers to include multiple functions and insulation testers, for example, may come with full -multimeter capabilities. However, multimeters and clamp meters have their own applications. Generally, the accuracy at very low currents on a multimeter will be vastly more accurate. Even when a true RMS clamp is utilized, below 0.5A, the reading can be suspect. Clamps are perfect for reading higher currents flowing through cables but useless for circuitboard current readings.”
UEi (www.ueitest.com), David Wheaton, said: “Accuracy and safety have all been improved, with advances in display technology making it easier to read the measured parameter.
“The trend we have observed is that clamp-on meters are now including digital multimeter functions such as full-range voltage and resistance in addition to the clamp current measurement capabilities.
“However, a true multimeter has the ability to measure current directly through the meter up to 10A in most cases. Clamp meters have traditionally used the clamp for current measurement and have not included the ability to measure less than 10A with the resolution and accuracy available on a true multimeter.”
GRIFFIN, a construction and tools writer from Oklahoma City, can be reached at firstname.lastname@example.org.