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SA Instrumentation & Control Buyers' Guide

Technews Industry Guide - IIoT 2018

Technews Industry Guide - Maintenance, Reliability & Asset Optimisation


Choosing the correct infrared thermometer
June 2009, Temperature Measurement

After time, temperature is the second most measured physical unit in production – as well as in quality control and maintenance.

Temperature represents an important indicator of product quality, safety and equipment conditions. Knowledge of the advantages and the limitations of this technology is needed if the correct infrared thermometer for the application is to be selected. It is also helpful to know the principal of operation of infrared thermometers.

During the last five years the IR sensor market has seen two major trends:


IR thermometers are significantly lower in cost. The most expensive part of an IR thermometer is the lens and detector. New lens materials and technologies (plastic, Fresnel lenses) and mass production of IR detectors have resulted in lower prices. Together, with the increased demand for industrial IR thermometers, high volume production of standard sensors has resulted in greater manufacturing efficiency for the IR thermometer manufacturers. Some types of IR sensors are up to 50% lower in cost than they were five years ago.


IR sensors are becoming smaller in size. In the past, the measurement of low temperatures made it necessary to use fast lenses with relatively large diameters in order to capture enough emitted energy. Progress in detector technology has helped reduce the dimensions of the IR sensing head dramatically. Because the newer sensors exhibit greater sensitivity they require less input energy to produce a usable output signal. As a result, lenses can have smaller diameters. The diameter of a lens may be only a few millimetres, but the sensor has a temperature resolution as fine as 0,1°C, and can measure down to -40°C.

The advantages of IR thermometers are:

* Fast response time (millisecond range), user gets more information per time period.

* Measure the temperature of objects that are moving, rotating or vibrating.

* Measure high temperatures up to 3000°C. (Contact probes will not work or have a short lifetime at high temperatures.)

* No mechanical damage or contamination of the surface (painted surfaces, food, and soft plastics).

* Measure actual product being manufactured instead of another part of the process or inferred measurement.

IR thermometers have special requirements:

* Must have direct line-of-sight.

* The optics of IR thermometers need to be protected against dust or condensation (a variety of accessories are available).

* In general, IR thermometers measure only surface temperatures and the ability to emit thermal radiation depends on the kind of material and especially on the surface finish.

Choice of IR unit

The operating wavelength of the instrument must coincide with that of the application in order for reliable, accurate measurement. It is best to use the shortest possible wavelength for the temperature range and Figure 1 indicates the common wavelengths used with respect to target temperature and error. From this it can be seen that to measure above 900°C one would not use the common 8-14 μm instrument, but rather one having a sensor rated for 1 or 2 μm wavelength.

Figure 1. Target temperature (°C) with emmisivity assumed to be 10% and the ambient temperature lower than the target. This graph clearly illustrates how the wavelength affects the accuracy of the measurement
Figure 1. Target temperature (°C) with emmisivity assumed to be 10% and the ambient temperature lower than the target. This graph clearly illustrates how the wavelength affects the accuracy of the measurement

These factors are important when choosing the correct IR thermometer. Note that there are many units on the market that quote low error on high temperatures and have the wrong wavelength detector. (For example, a range of -50 to 1500°C with a 8–14 μm wavelength.)

Advances in IR thermometer electronic design

Process industries continue to need sensors with higher accuracy and repeatability as they look for ways to cut costs, maximise their production lines, and monitor quality. Easy installation, use, and maintenance continue to be important, as does the ability to withstand harsh environmental conditions. Field checking and field calibration features are becoming more and more important as companies look to optimise their personnel and equipment resources. Manufacturers need IR sensors with a wide operating temperature range that covers more applications and eliminates the demand for water/air-cooled housing, which keeps the cost down due to less water/air consumption and hardware required.

Advances to detectors and optics of infrared thermometers are helping manufacturers and their customers expand the types of applications where IR can be used effectively, gain speed and accuracy, and get a better return on their investments. Two-colour or ratio measurement and units with built-in visual cameras are some of the recent advances.

Raytek and Ircon, suppliers in the infrared measurement industry, design, manufacture, and market a complete line of online and portable noncontact thermometers (IS units included) and line scanners for industrial, maintenance, and quality control applications.

R&C Instrumentation is offering a simple handbook which explains the principles and types of measurement. The handbook covers important factors like different frequencies for different temperatures and single and two colour (ratio) operations. (For a free copy of this handbook e-mail R&C Instrumentation at the address below.)

Supplied By: R&C Instrumentation
Tel: +27 32 946 2805
Fax: 086 622 6050
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Further reading:

  • Paper mill saves with IR window program
    December 2018, R&C Instrumentation, Maintenance, Test & Measurement, Calibration
    In search of alternate methods for conducting safer inspections, the reliability engineer investigated how infrared inspection windows (IR windows) might be utilised.
  • Temperature measurement within the plastics industry
    December 2018, Instrotech, Temperature Measurement
    Temperature is an important measurement parameter for many process techniques used in the plastics industry. Non-contact temperature measurement using an infrared sensor system is therefore an effective ...
  • Emerson’s compact new hygienic transmitters
    December 2018, Emerson Automation Solutions, Temperature Measurement
    Emerson has unveiled a new line of compact transmitters. Designed specifically for hygienic applications in the food and beverage industry, they will enable manufacturers to minimise downtime and lower ...
  • IRt/c setup with auto-tune ­temperature controllers
    November 2018, Temperature Controls, Temperature Measurement
    In many applications, heating elements are employed to heat a product in an oven, furnace, or with jets of hot air. Conventional control devices using contact thermocouples, measure and control the oven ...
  • SpotScan gives pyrometers ­scanning ability
    November 2018, R&C Instrumentation, Temperature Measurement
    Fluke Process Instruments recently introduced the SpotScan line scanning accessory for the Endurance, Marathon, and Modline ranges of IR non-contact temperature measurement sensors. The accessory features ...
  • Safety temperature measurement device for boilers
    October 2018, GHM Messtechnik SA, Temperature Measurement
    The Safety-TL4896, a SIL2 rated temperature measuring device from Martens, conforms to international boiler regulations and offers a unique front panel installation. Certified to DIN EN14597 and DIN EN61508, ...
  • Raytek pyrometer sensor now in 4-20 mA
    October 2018, R&C Instrumentation, Temperature Measurement
    About a decade ago, Raytek introduced the CM, a compact, integrated IR non-contact thermometer intended for quick and seamless replacement of J and K-type thermocouples. The CM, still an industry favourite, ...
  • Temperature sensor with drift monitoring
    October 2018, ifm Electronic RSA, Temperature Measurement
    The sensors of ifm electronics’ TAD series have two resistance elements with different characteristics (PT and NTC) that monitor each other permanently in the process. Drift is immediately detected and ...
  • Resistance thermometer for harsh conditions
    September 2018, Instrotech, Temperature Measurement
    Due to their extreme insensitivity to vibration, impact and shock load, Kobold’s TNK resistance thermometers are particularly suitable for monitoring the temperature of diesel engines. The extremely robust ...
  • ThermoView for industrial thermal imaging applications
    September 2018, R&C Instrumentation, Temperature Measurement
    Fluke Process Instruments recently announced the ThermoView TV40, a high-performance industrial thermal imager designed for the most challenging environmental conditions. Supported by intuitive and powerful ...
  • Temperature transmitter with new HART protocol
    September 2018, WIKA Instruments, Temperature Measurement
    The T32.xS temperature transmitter from WIKA is now also available in a version that communicates via the new HART 7 protocol. Another new function is an extended measuring point description (Long Tag). ...
  • Smart pyrometers for factory ­automation
    August 2018, R&C Instrumentation, Temperature Measurement
    Fluke Process Instruments has launched the Thermalert 4.0 spot pyrometer series for automatic non-contact temperature monitoring between -40 and 2250°C. The series currently comprises 13 models with varied ...

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