Finding the Right Clamp Meter: Smart Tool, Smart Buy

When you are responsible for installations, maintenance, repairs, and overhauls of "everything utility," your toolbox can fill up pretty quickly with all the tools and test equipment needed to constantly change gears from job to job.

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By Andre Rebelo

When you are responsible for installations, maintenance, repairs, and overhauls of "everything utility," your toolbox can fill up pretty quickly with all the tools and test equipment needed to constantly change gears from job to job. Jobs can range from electrical testing, to operating temperature measurements, to system diagnostics and general troubleshooting. For many of these jobs, a multi-function clamp meter designed for the industrial setting can help you with essential electrical readings such as current, voltage, and temperature. For most clamp meters, "multi-functionality" means having these three essential functions in one tool: a clamp meter, a multimeter and a thermometer capable of readings via an external Type-K probe. But the truth is, the complexity of today's utility infrastructure demands other functions as well, such as non-contact voltage detection, non-contact infrared temperature readings, and thermometry capabilities to take temperatures at two different spots.

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You quickly realize that besides carrying a 3-in-1 clamp meter, you need numerous other test devices to get your job done effectively and safely. Ideally, your clamp meter should be equipped with additional functions to help you save on equipment spending and to get more done with less equipment.

Here are examples of other important testing functions that an industrial MRO professional uses day in and day out:

Infrared Thermometer
An infrared (IR) thermometer is indispensable if you need to measure temperatures at a distance due to limited access or safety issues. With a built-in laser beam to ensure precise targeting of the desired measurement spot, an IR thermometer is as quick as it is useful. While a 3-in-1 clamp typically does offer Type K one input for temperature readings, an IR thermometer can prove handy in a number of situations. Examples include: measuring air temperature from a cooling vent; taking a reading on a live surface such as a breaker panel or motor control; performing spot maintenance checks to see if equipment is running too hot; or scanning coolant temperatures for abnormal readings.

Differential Temperature Type K Thermometer
On the subject of temperature, getting a differential temperature reading or "delta T" from two different areas in a coolant system determines superheat or subcooling temperatures. These versatile values can help a technician isolate problematic cooling issues such as under- or overcharge, an overfeeding metering device, restricted or misdirected airflow, restrictions in refrigerant liquid lines, or insufficient condenser cooling from poor air or water flow. To get a delta T measurement, you need to perform two temperature measurements.

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If your clamp-meter only features one Type-K thermocouple input, you'll need another device such as a multimeter or a separate Type K thermometer to get that second simultaneous reading. In some cases, technicians use a dual type-K thermometer to take both readings. With dual temperature probe inputs and a built-in T1 minus T2 function, a dual thermometer automatically gives you a differential value that is useful in determining the superheat or subcooling temperature for a refrigeration system without temperature charts and without a calculator.

Non-Contact Voltage Detector
One safety and diagnostic must-have is a non-contact voltage detector. If you are on a site where vital equipment is down for example, and you need to check quickly and easily for the presence of voltage around an area where repairs need to be performed, a non-contact voltage (NCV) detector is invaluable. With an NCV detector, this vital first-step safety check easily alerts you with visible and audible alarms if live voltage is nearby that should be avoided or powered down.

Finding Best-in-Class Functionality

Utility MRO professionals should keep the following specifications in mind when selecting clamp meters and related test equipment:

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Clamp Meter

  • Most clamp meters measure AC current. Look for a clamp meter with the added ability to measure DC current. This offers significant convenience when working on increasingly prevalent DC components in alternative energy systems.
  • In addition to AC/DC current versatility, clamp meters are as useful as their current and voltage rating. Selecting a 400A and 600V clamp meter at a minimum assures safety and usefulness in a variety of applications.
  • At its heart, a clamp meter is a multimeter with amperage-measuring capabilities. As such, industrial users should ensure their clamp meter offers advanced multimeter capabilities. What makes a multimeter advanced?
    • True-RMS test tools ensure readings from non-linear loads are accurate. As power semiconductors and rectifiers make their way into newer components and controls, a meter must compensate for current being drawn in short pulses instead of a clean sine wave. A meter that is not true-RMS can be off by as much as 40 percent when measuring such line side currents.
    • Does the meter offer high-resolution readings? In other words, how fine are the differences that can be read by the meter? Some clamp meters offer voltage and current resolution as granular as 0.01mV and 10mA, as well as 0.01nF for capacitance, and 0.001Hz for frequency.
    • Does the clamp meter support specialized tasks such as a DC MicroAmp (µA) mode (useful for flame rod system testing)? If so, look for 0.01µA resolution.
    • Cat 3 600V ratings ensure sufficient protection on the load side of the service fuses to withstand a 6kV transient over-voltage.
  • Is it rugged? All that functionality is useless if it breaks when dropped. Look for designs that are built to handle rough use such as a housing that is double-molded, effectively providing two layers of protection.

Infrared and Type K Thermometers

  • When selecting an infrared thermometer, it's important to find a temperature range that accommodates your typical measurements. For pros, a -50°C to 270°C range covers most non-contact measurement scenarios.
  • As mentioned above, having a thermometer with two Type K thermocouple inputs and an automatic delta T differential temperature function eliminates the hassle of calculating temps from two devices. A wide measurement range from -50°C to 1000°C ensures the thermometer's versatility.
  • For temperature measurements on pipes, lines, or tubing, having equipment that supports the option to use a clamp-style pipe probe for easy, hands-free temperature measurements without tape or Velcro fasteners is a must-have.

A Newer, Economical Alternative: Industry's First 5-in-1 Clamp Meter

It's clear from this buyer's guide that, for effective utility and industrial troubleshooting techniques, multiple tools are frequently required. One company is taking a different approach suggesting that multiple functions are required, but not always multiple tools. Extech Instruments recently introduced their EX623, the industry's only 5-in-1 clamp meter. In addition to standard 3-in-1 capabilities found in most clamp meters (clamp meter, true-rms multimeter, and Type K thermometer), the EX623 offers a built-in infrared thermometer (a patented Extech feature) and an integrated non-contact voltage detector. Additionally, its thermocouple-based thermometer is upgraded to two Type K inputs and offers an automatic differential temperature function. The EX623 costs significantly less than a set of similar, separate tools and also takes up less room in the toolbox.

By combining key testing functions that a maintenance-repair-operations technician uses day in and day out with best-in-class specifications, the Extech EX623 is receiving many positive reviews around the world. The 5-in-1 was recently awarded the Gold Industrial Electronics Innovation and Technology Award at the Hong Kong Electronics Fair, Asia's biggest electronics event. Judges at the competition remarked that award winners not only demonstrated sophisticated product designs, but also offered appealing value in this challenging economic climate.

Smart Techs Looking for Smart Tools, Smart Buys

It's easy to see why technicians rely on the versatility, ruggedness and accuracy of their testers and meters. Whether it's 3-in-1 versus 5-in-1, or the indispensible use of non-contact tools such as IR thermometers and voltage detectors, the test equipment market has changed dramatically in recent years. While some buyers will always shop by brand, the current economic climate has tightened budgets around the world. Many more utilities and individual techs are now taking a closer look at side-by-side comparisons of product specifications before opening their wallets. With this multifunction clamp-on meter guide in hand, buyers can identify key functions and specs that should be on everyone's must-have list. After all, for many technicians, shopping for new test equipment not only means finding a smart tool but a smart buy.


About the Author:
Andre Rebelo, Global Communications Manager, Extech Instruments, a FLIR Company, enjoys talking with customers to learn more about how they are using Extech testers and meters in their day-to-day job. Follow him on Twitter: arebelo.

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