Whatever the process, non-contact infrared thermometry allows quick and accurate temperature measurement. Scott R Williams shows how.

Accurate, ongoing temperature measurements are crucial in literally every industry where temperature plays a role in production processes, whether in the manufacture of chemicals, glass, plastics and metals, or in web processes such as film coating, paper and textile printing. The list goes on. Surface temperature is a very good indicator of how well your process and production equipment are running. Regular temperature measurement should therefore be at the top of your list of things to monitor on a continuous basis.

The automatic monitoring and control of process temperatures allows you to immediately detect over- or under-heating of material surfaces, so that you can quickly make in-process adjustments, eliminate scrap and improve efficiency. To accomplish this, there are two basic methods for measuring surface temperatures: contact or non-contact. For the majority of industrial applications, non-contact infrared (IR) temperature measurement is a far better choice, as it ensures safety, minimises material waste and increases productivity.

A contact thermometer, or thermocouple, requires you to come into contact with the surface, which can alter its temperature, or otherwise tear or contaminate the product you are measuring. On the other hand, a non-contact IR thermometer allows safe and accurate temperature measurements of objects that are moving, extremely hot or difficult to reach without affecting the surface. IR thermometers are also unaffected by high target temperatures, which could damage or destroy a contact thermometer.

Compared with thermocouples, non-contact IR thermometers also have an extremely fast response time - within milliseconds - and can be used from an optimal distance with high accuracy. Measuring at a distance from the target also means that the sensor can be located in a more acceptable environment without being compromised by damaging heat, vibrations, and optical interferences like dust, water spray and steam. This extends the life of the instrument and protects a plant's investment in such equipment.

Non-contact, infrared (IR) pyrometers have been used extensively for many years to measure process temperatures. Here's how this non-contact solution works - the infrared energy that is naturally emitted from all objects is measured without coming into contact with these objects. Every form of matter with a temperature above absolute zero emits infrared radiation according to its temperature. The cause of this is the internal movement of molecules. The intensity of this movement depends on the temperature of the object.

An IR thermometer can be compared to the human eye. The lens of the eye represents the optics through which the radiation from the object reaches the photosensitive layer via the atmosphere. This is converted into a signal that is sent to the brain. Very similar to the human eye, when pointed at the measurement target, the IR thermometer captures radiated energy as it passes through the atmosphere, directs it through its optical system, and converts it into an electrical signal. This signal is displayed instantly in degrees Celsius on the unit's LED readout, or in tables or graphs on a PC with the help of software.

These devices are indispensable for monitoring the overall temperature and managing the operating economy of industrial equipment and processes. However, the need to continuously improve operating efficiencies, enhance product quality, and implement more efficient control strategies imposes continuing demands on the capabilities of infrared thermometers.

The latest digital IR temperature sensors have built-in microprocessors, two-way remote digital communications, and easy-to-use analysis and trending software to support detailed tracking of problems that arise in manufacturing and enable product identification and traceability.

Built-in RS-232 or RS-485 serial communications enables the remote control of multiple temperature sensors, placed at critical points along a production line, and the capture of real-time digital temperature data for ongoing analysis and quality control. Using continuously recorded digital output from IR temperature sensors, engineers can pinpoint the time and location in which the process was out of specification and identify the products affected.

There is a variety of IR sensors to select from for reliable, non-contact temperature measurement on the plant floor or in the R&D lab. Fix-mount IR process imaging line scanners and ratio thermometers are used to continuously monitor temperature at critical points along the production line.

Handheld units are used for temperature spot checks of product batches and during routine maintenance inspections of process equipment.

Where edge-to-edge surface temperature profiles are needed to control product uniformity, thermal imaging line scanners provide real-time views of critical surfaces in production processes, and can be installed at strategic points for instant hot or cold spot detection. Using a highly sensitive detector, a line scanner collects infrared radiation from a surface passing under its field of view and presents the data instantly in the form of a 2-D thermal map of the surface. The visual information afforded by such a device allows you to see current status and react quickly to problems.

In high temperatures and production environments with heavy dust, steam or smoke levels, accurate temperature measurement is often a challenge to say the least. High temperatures can damage sensitive electronics, and air laden with particulate can obscure readings. If this is the case, mounted ratio, or two-colour, IR thermometers are necessary for reliable measurements of your process temperatures. The ratio of energy detected in two different narrow spectral bands is used to calculate the true temperature.

A stable reading is possible even under the most challenging of environmental conditions, for example in controlled cooling areas where steam and dust can block up to 95percent of the field of view.

For less challenging ambient conditions, where there is a clear field of view between the target and the instrument, a single wavelength IR sensor is sufficient to do the job.
As with ratio pyrometers, multiple single wavelength sensors can be linked together in a networked multi-drop configuration to measure several spots at once along the production line. Some sensors are so small that they can be easily integrated into equipment to measure temperature in tight spaces.

In addition to fixed-mounted sensors, high-precision handheld IR thermometers are available with advanced features to check product quality or for use in the maintenance of your production equipment. These include data logging, or the ability to capture and store temperature data for multiple locations along an inspection route, photographic documentation and temperature trend analysis supported by software on a PC.

Scott R Williams is European Marketing Specialist at Raytek GmbH in Berlin, Germany, tel +49 30 478 008 805, email swilliams@raytek.de. More information is available from Raytek in Germany on +49 30 478 00 80, or the UK on +44 1908 630800.