Temperature Measurement


The evolution of infrared line scanning technology

March 2022 Temperature Measurement

Infrared (IR) line scanning has been around for decades, and today this technology is used throughout the process and discrete manufacturing industries. IR line scanners offer an effective online monitoring solution for obtaining a complete temperature profile or image of a moving product. Such scanners are easily integrated into process equipment for continuous temperature monitoring and trend analysis.

An infrared line scanner provides a ‘picture’ of the surface temperatures across a moving product, such as metal slabs, glass, textiles, coiled metal or plastics. The scanner includes a lens, a rotating mirror that scans across the lens’ field of view, a detector that takes readings as the mirror rotates, and a microprocessor to interpret the data.


R&C Instrumentation supplies Raytek’s range of line scanners.

As the mirror rotates, the line scanner takes multiple measurements across the entire surface, obtaining a full-width temperature profile of the product. As the product moves forward under the sensor, successive scans provide a profile of the entire product, from edge to edge and from beginning to end. This data may be processed within the line scanner itself to create alarms or other outputs, or it may be transferred to a PC for higher-level processing.

The computer converts the temperature profile into a thermographic image of the product, with various colours representing temperatures, or it can produce a ‘map’ of the product. The measurement points across the width can be arranged in zones, averaged, and used to control upstream devices such as cooling systems, injectors or coating systems.

The wide field of view of a line scanner allows a 1:2 ratio of distance to product size, which permits continuous fixed scanning of very wide objects such as cement kilns or close-proximity processes such as glass float lines. Unlike lightweight handheld portable IR scanners, fixed-head process line scanners tend to be robust instruments with built-in features such as air purging, water cooling and protective windows. They are often incorporated into monitoring or alarming and control systems with factory-floor interfaces.

Latest technology advancements

In recent years, instrumentation manufacturers have introduced a new generation of infrared line scanners specifically designed for automated, high-speed, discrete and continuous manufacturing processes. These systems feature the latest electronics, optics, communications and mirror mechanisms.

End users can now select rugged line scanners designed with cast aluminium housings and integrated water cooling. Intended for use in highly demanding industrial environments, the scanners also utilise an integral air-purge collar, producing laminar airflow across the scanner window to prevent contamination build-up.

To speed up alignment, some line scanners employ an internal line laser, which indicates the exact line-of-sight of the unit. This laser, protected by the line scanner housing, projects a visible laser line on the target even while the line scanner is collecting data at full speed.

The most advanced infrared line scanners have achieved scan speeds of up to 150 Hz – well in excess of earlier scanner technology – and can deliver over 1000 measurement data points. Increased scan speed allows the IR system to gather high-resolution data from even the fastest manufacturing processes. It also allows rapid detection of temperature variations and hot spots, such as those commonly found in food drying and plastics processing applications.

In addition, thermal images from multiple line scanners can now be combined with related process measurements on a single PC-based system. The scanners’ display formats typically include thermal image, thermal profile, 3D waterfall and sector trending. Facilities can include rolling buffer snapshots, zone/sector alarms, configuration recipes and history review.

Infrared line scanner technology has further benefited from the development of real-time, Windows-based thermal imaging software, contour graphs and thermograms in multiple windows. Users can select a portion of the thermal image and zoom in for a more detailed view, or compare a stored reference image with the current image to ensure consistency. The software automatically triggers an alarm when the temperature falls outside of the desired range and produces a report showing the exact location and time of occurrence.

Adoption of industrial Ethernet

The demand for digital communications challenges instrument manufacturers to offer cost-effective products that do not restrict interface choices. This is not an easy undertaking. Generally speaking, the proliferation of disparate bus structures, dissimilar hardware and different software precludes general connectivity or interoperability.

The major influence driving current network trends emanates not from the industrial sector of our economy, but from the commercial sector – namely, the rapidly growing digital business community fuelled by enterprise-wide Ethernet and Internet, and TCP/IP-compliant systems and software.

When Ethernet first arrived a couple of decades ago, its use for industrial automation networking was dismissed. But usage has steadily increased in the automation environment and Ethernet-ready products for device-level networks continue to expand. Most plant engineers have installed some sort of Ethernet network in their homes, so the technology is already seen as familiar and user-friendly.

The big advantage with industrial Ethernet is the ability to standardise an entire enterprise – from the plant floor to the corporate boardroom – on one network, providing access to data from anywhere around the world. Ethernet networks provide an infrastructure to acquire, view, process and transmit files, graphics and information over a company’s intranet or the Internet. The increased use of industrial PCs on the factory floor reinforces this trend. This, in turn, influences trends in industrial software.

Ethernet reduces installation costs by eliminating the need to run wires for connecting various field devices and computers to a PLC or DCS. The user simply connects an Ethernet-compatible device to the nearest Ethernet hub. This technology also removes the constraints of proprietary network protocols, offering greater openness and accessibility to the network architecture.

Industrial Ethernet is fast becoming a universal networking systems interface for all types of measurement and control devices – including non-contact IR temperature measurement equipment. Unlike the RS-485 protocol, Ethernet supports the increased data flow rates of modern IR line scanners. It also offers the prioritisation and robustness essential for industrial automation networks.

Today’s new breed of IR scanner offers an on-board Ethernet TCP/IP communication capability. Within an existing industrial Ethernet infrastructure, users can connect directly to these scanners without the need to go through manufacturer-specific software or run wiring to proprietary controllers or connection boxes. Just like a network printer, the line scanner can be assigned a unique IP address and accessed from any computer in the factory. This innovation has a considerable effect on the total installed cost, eliminating additional wiring, conduits, etc., while at the same time providing unprecedented access to process data.

Growth of open protocols

Traditionally, large process control manufacturers built significant volumes of interconnected technologies, all communicating using common communication protocols. With equipment (instruments and/or software) provided by any one supplier, the user was ensured that communication would be easy to set up and robust in operation. Picking the best of each sensor type on the market was not possible. Further, smaller niche manufacturers could not provide their technology in a useful format without creating multiple versions, one for each protocol – a process which resulted in extremely high licence fees and huge product complexity.

Industrial end users, who need to run software on their process control systems, now strongly advocate the move to open systems. Object-oriented technology, object linking and OLE (Object Linking and Embedding) for Process Control (OPC) are at the forefront of this trend. OPC provides increased interoperability and facilitates the exchange of information among different sensors, automation devices, control systems and production applications running across an entire manufacturing enterprise. With open network protocols, a user can modify one part of the system without affecting communications to other areas.

For example, plants utilising thermal imaging software with OPC server functionality can integrate infrared line scanners with an OPC-compliant distributed control interface (DCI) or human machine interface (HMI) system. OPC makes it easier to integrate measurement devices into different plant information systems by standardising the interfaces between dissimilar software and hardware. OPC software drivers allow full interoperability with instruments using third-party, OPC-compliant software. The creation of these drivers by instrument manufacturers will help minimise their involvement in software development (at least at the application level), allowing them to focus on sensor and measurement technology.

Conclusion

Like other process measurement technologies, non-contact infrared line scanning has undergone much advancement in recent years – offering users robust new capabilities for controlling fast-moving production processes and eliminating a host of temperature-related problems. Instrumentation manufacturers are responding to industry demands by designing IR scanners that not only provide better online performance, but also greater simplicity and ease of use.

For more information contact R&C; Instrumentation, +27 11 608 1551, info@randci.co.za, www.randci.co.za


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