INFRARED: FASTER, SMALLER, CHEAPER

Judging by the number of manufacturers prepared to commit a significant slice of their profits to R&D, non-contact thermometry is a dynamic technology. Fast, remote, able to measure temperatures in excess of 3,000srC and to produce output signals which are compatible with virtually any control system, IR sensing devices don’t touch or contaminate the object […]

Judging by the number of manufacturers prepared to commit a significant slice of their profits to R&D, non-contact thermometry is a dynamic technology.

Fast, remote, able to measure temperatures in excess of 3,000srC and to produce output signals which are compatible with virtually any control system, IR sensing devices don’t touch or contaminate the object they’re measuring and…they’re getting cheaper.

`There have, without doubt, been some startling developments in IR in the last 12 months’, says Calex Instrumentation’s applications manager, Dr Fred Ritchie.

`Miniaturisation, smarter electronics and sensing have all played their role in improving the technology while bringing down the cost’.

The trend is towards small, self- contained heads capable of feeding a wide spectrum of data acquisition equipment and being controlled by PC or PLC. When you look at the size of the temperature sensor market, it isn’t surprising that so much has happened so quickly. Precision temperature measurement improves product quality, increases productivity and reduces downtime by ensuring that processes are operating consistently, under optimum conditions. So temperature measurement accounts for an estimated 75-80% of the sensor market, globally. Most are still thermocouples and RTDs, but IR is catching up fast.

Benefits are speed (the response of commercial IR sensors is measured in milliseconds, not seconds), miniaturisation (typically 12 mm in diameter and only 100mm in length) and the ability to output signals in a fashion similar to that of traditional thermocouples (producing an output value linear with the voltage signal – 10mV/srC – or 4-20mA), all, in some circumstances, for less than £200. Not that long ago, similar technology was packaged the size of a battery-operated torch and would have cost ten times that amount.

One of the most significant developments of the last decade has also been the vast increase in accuracy at lower temperatures. Ten years ago low temperature IR devices were noisy and subject to unacceptable stability drift. Now, it is possible to measure to temperatures as low as -100srC with minimal noise and drift – routinely, at temperatures of -50 or -30srC.

Optical resolution has improved as well, with 10:1 availability almost the norm, says Raytek’s general manager Peter Clarke, whose own company offers such a device with 4-20mA output in the £200 range.

The increase in the spectrum of industries in which hand held devices are now used is equally impressive. Portable infrared sensors are used regularly for maintenance, resulting in early detection of problems that could otherwise result in expensive equipment replacement or shut down production completely.

It is used by Formula One motor racing teams to check tyre temperatures, and environmental health officers to ascertain food temperatures. Some 1,500 hand-held units have been purchased by one supermarket alone, says Clarke.

ISO 9000 has given a further impetus to the need to quantify production parameters – including temperature – and this has led to still more use of non-contact technology.

IR is now a real-time closed-loop controlled product, and remote addressability is a positive option.

Thermal imaging has also made its mark in recent years. IR technology affords more than simple single point measurement. Focal plane arrays can provide a snapshot of a thermal image in a single go – no more the time-consuming scanning by a single detector. Equipment typically includes a focal plane array of 70-80,000 individual sensors. It can cost around £40,000, but it can give an immediate thermal picture.

An example of the technology is the ThermaCAM from Inframetrics, and a typical application is for predictive maintenance. Its full-colour viewfinder spotlights potential trouble. Images can be saved to a PCMCIA memory card and analysed on a laptop running Windows software.

Though now in their middle-age, dual-wavelength pyrometers nevertheless continue to make an impact in `dirty’ industries. This is because they provide improved accuracy over standard one-colour instruments in difficult applications where the target is smaller than the thermometer’s field of view, where it’s obstructed or where the energy that reaches the instrument is attenuated because of atmospheric conditions.

Ratio thermometers are more accurate in these conditions because they determine temperature from the ratio of the infrared energy emitted by a target at two separate wavelengths. Improvements in this area mean obscuration of the sensor window up to 90% produces an accuracy deviation of only 1%, typically. The offshore industry loves them. Stack maintenance and cleaning becomes almost an irrelevance.

Non-contact thermomety is these days about detecting the IR radiation, processing the signal and producing an output proportional to the temperature. Equipment can be self-calibrating. Coupled to a PC for control, with all the user-friendly software benefits that entails, it is a trend still in its ascendancy.

IR devices are available for general applications off-the-shelf or from a catalogue. But more and more, as the option to go to non-contact technology offers solutions to measurement problems, specialists are being approached for custom devices. And that, increasingly, means offering the ability to come up with turnkey systems, even to the point of putting data on an ethernet for dissemination to a range of in-house facilities, such as quality records, etc, according to technical director for Land Infrared, Dr Geoff Beynon.

Land’s Tom McDougall agrees. `Part of the market is application-led,’ he told C&I. `Typical requirements demand the equipment should be robust, and this is particularly true in the steel industry, where the environment is especially hostile and reaches exceptionally high temperatures. There is a move here towards the use of fibre optics as opposed to lens-based devices, to eliminate the need for cooling. This prolongs the life of the device and reduces the need for maintenance.’

Building brick production is among the biggest beneficiaries of new non-contact thermometry technology with, according to ACT Controls’ sales manager, Nathan Neal, productivity improvements up to 25%.

ACT is into systems integration. And the customer in this case is the brick producer which is newly discovering the benefits of non-intrusive temperature measurement. `The great benefit of IR devices to this industry is that you can focus on an item in the kiln; you don’t have to rely on air temperature measurements. Also, the new devices can still `see’ through gases and dust, and that’s important in this industry’.

New developments at Land Infrared open up fresh opportunities for process control using the Landscan linescanner, which produces a large array of spot temperature measurements in the form of a thermal map, the data from which is processed by a PC.