Over the last 30 years non-contact temperature measurement devices, using infrared technology, have been introduced world-wide into many industries and applications. Consistent product temperature profiles are critical in continuous web and rotating equipment production applications. A variety of detectors with differing spectral response enable users to select sensors depending on the object and application.
Principle of operation
Infrared line-scanners measure multiple temperature points across the surface of the material. A motorised mirror scans the surface at speeds of up to 20 lines per second (20 Hz). A lens assembly collects the infrared radiation from 256 points within a 90° field-of-view, and the energy is transferred through a band-pass filter onto a sensitive photo-detector.
The signal is amplified prior to digitising and then processed in realtime to determine the temperature of the measured points. High scan and data transmission speeds enable rapid online thermal imaging of fast moving extrusion processes. Connection to a standard personal computer allows the temperature data to be visualised as a line graph and a multicolour thermal image simultaneously. Temperature profiles and images can be saved for future analysis or printed out for customer documentation and quality certification requirements.
The graphic software displays realtime profiles and thermal images of edge-to-edge product temperature. Machine operators can zoom into the temperature profiles to get a closer look for instant on-screen analysis. Using these graphical displays, operators can detect process temperature non-uniformities and make immediate adjustments. RS485 communications between the scanner control-room allow remote support and configuration of the device.
Benefits and applications
Compared to thermocouples and RTDs, non-contact thermometers have a response time of milliseconds and can be used from a distance with high accuracy. This means the sensor can be located remotely and protected from the harsh environments encountered in paper and steel production. The MP50 line-scanner from Raytek, with an MTBF of 40 000 hours, has been developed with these criteria in mind. Pre-processing, linearisation, calibration and calculation of true temperature are performed entirely in the scanner. The data is then transmitted via a high-speed serial link for post-processing.
Typical applications for the infrared scanner include high-speed rotating soft calendar rolls, plastic and steel extrusion machinery and slow-speed rotating kilns. Infrared scanners can also be used for area inspections such as monitoring temperature changes in factory areas or in process bins.
Raytek has developed many software applications to run with the MP50 scanner. These include:
* SS100 – to monitor surface temperature and defects on fast rotating soft calendar rolls.
* CS200 – for rotating kilns.
* EC and ES100 – for surface inspection in extrusion processes.
* GS100 – for sheet monitoring in glass production.
* TF100 – for thermoforming applications.
The company also develops custom software packages for unique customer requirements.
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