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Publication Date: 08/1/2009
Archive >  August 2009 Issue >  Special Features: Test and Measurement > 

Clamp Meters: Getting the Most-Needed Functions
This single clamp-on instrument has multiple built-in functions, replacing several different measuring tools.

When you are responsible for installations, maintenance, repairs, and overhauls of "everything industrial," 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 on pumps, motor controls, and boilers, to heating and cooling measurements, to lift and conveyance systems diagnostics, to furnace, flame signal, and compressor 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 complexity of today's plant systems 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.

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 (Maintenance, Repair, and Operations) 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 input for temperature readings, an IR thermometer can prove handy in a number of situations. Examples include: measuring air temperature from a ceiling duct; taking a reading on a live surface such as a circuit breaker or motor control; performing spot maintenance checks to see if motors or bearings are running too hot; or scanning evaporator coil and suction line temperatures for abnormal readings. Getting a differential temperature reading or "delta T" from two different areas in a refrigeration system determines superheat or subcooling temperatures. These versatile values can help a technician isolate problematic HVAC 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.

If your clamp-meter only has 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 provides 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, 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 — voltage that should be avoided or powered down.

MRO professionals should look for certain specifications when selecting clamp meters and related test equipment. 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 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 adjustable speed motor drives and heating 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.

High resolution: Does the meter offer high-resolution readings? 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.

Specialized measurements: 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.

Load protection: Cat 3 600V ratings ensure sufficient protection on the load side of the service fuses to withstand a 6kV transient over-voltage.

Ruggedness: Is it rugged? All that functionality is useless if the instrument 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.

I-R 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 to +270°C range covers most non-contact measurement scenarios.

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 to +1000°C ensures the thermometer's versatility.

For temperature measurements on pipes 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.

First 5-in-1 Clamp Meter
For effective industrial plant troubleshooting, multiple measuring tools are frequently required. One company is taking a different approach suggesting instead that multiple functions are required on a single tool. Extech Instruments recently introduced its 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 new instrument offers a built-in infrared thermometer (a patented feature) and an integrated non-contact voltage detector. In addition, 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 a lot less room in the toolbox.

By combining key testing functions that a plant MRO technician uses day in and day out with best-in-class specifications, the new instrument has been 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 reflected appealing value in this challenging economic climate.

Technicians must of necessity rely on the versatility, ruggedness and accuracy of their testers and meters. Whether it's 3-in-1 versus 5-in-1, or the indispensable 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, many more are 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.

Contact: Extech Instruments, 285 Bear Hill Rd., Waltham, MA 02451-1064 781-890-7440 fax: 781-890-7864 E-mail: Web:

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