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FEATURE THERMAL IMAGING


TAKING TEMPERATURE OF GLASS T


Temperature is a key measurement parameter in controlling the quality of glass or glass products but current thermal imaging technology is limited in the accuracy it can achieve


emperature is a key measurement parameter in controlling the quality


of glass or glass products. Inline (fixed) thermal imaging cameras or non-contact infrared temperature sensors can be installed that measure the temperature of glass products and surfaces during production as well as glass substrates used in semiconductor processing and for the manufacture of solar cell panels, automotive glass, glass containers/tubes, light bulbs and LCD displays. However, current thermal imaging technology is limited in the accuracy it can achieve.


TEMPERATURE MEASUREMENT OF SHEET GLASS The latest addition to the Micro-Epsilon family of thermal imaging cameras is specifically designed for measurements on any glass objects. With a spectral range of 7.9µm the thermoIMAGER G7 accurately measures the temperature of even very thin glass. Conventional thermal imagers with spectral wavelengths of 8-14µm do not measure accurately the temperature of the glass. At longer wavelengths glass allows transmission of temperature from objects behind or near to the glass which gives inaccurate measurements, normally lower than the true glass temperature. Using the G7 camera at a wavelength of 7.9µm eliminates any transmission from other objects, resulting in very accurate glass temperature measurement. “When measuring at 7.9µm the glass


object becomes a solid body and only emits its own temperature,” comments managing director Chris Jones. “This results in very accurate temperature measurements even on very thin glass or thin walled objects such as glass tubes, bottles and substrates.”


REFLECTIVE COATING ADJUSTMENT Even if the glass has a protective (reflective) coating applied to it an additional reference pyrometer can be set up to provide an adjustment factor to the camera which corrects for this reduction in transmission of infrared temperature from the glass; a feature of the thermoIMAGER software supplied as standard with the G7. In addition, licence-free operating and


analysis software includes process control features such as ‘line scan mode’ which enables the camera to view through a narrow slit (restricted field of view) onto the glass yet still provide a complete


22 NOVEMBER 2015 | FACTORY EQUIPMENT


thermal image of the entire sheet. Powered and operated via a USB 2.0 interface the G7 provides temperature images and profiles of a target area. This plug-and-play unit enables the real time capture (at 80Hz full frame rate) and storage of images or video of an event for slow motion play back or snapshots at a later date; a key feature in many quality, inspection, R&D and failure diagnostics work. The G7 is lightweight (320g) and compact (46 x 56 x 90mm) and operates in ambient temperatures of 0°C to +70°C (+240°C with an integrated cooling jacket).


HIGH PERFORMANCE IR TEMPERATURE SENSOR An alternative method of measuring the temperature of glass and glass products is to use a high precision infrared temperature sensor. Micro-Epsilon’s thermoMETER CT


family of infrared temperature sensors includes the CTLaserGLASS, a non- contact infrared thermometer specifically designed to measure the temperature of glass surfaces or products such as solar panels, flat glass lines, light bulbs, car glass finishing and glass containers. The CTLaserGLASS uses a 5.0µm


wavelength detector to accurately measure temperatures from 100°C up to 1,650°C. The average measuring wavelength of 5.0µm provides a low depth of penetration and enables reflection effects to occur for the infrared measurement of glass. Using shorter wavelengths than this would mean the sensor would measure through the glass rather than measuring the true temperature of the glass itself. In container glass production for example, the operator must obtain the


Even if the glass has a protective coating applied to it an additional reference pyrometer can be set up to provide an adjustment factor to the camera which corrects for this reduction in transmission of infrared temperature from the glass


temperature of the glass gob (molten glass that is poured into a blow mould) to observe the ratio between glass viscosity and gob weight. The mould temperature measurement


is therefore critical for balancing the cooling levels of mould shells. In the production of flat, automotive and construction glass, homogeneity of the complete panel is important, particularly when it comes to bending, annealing and tempering zones. The double laser aiming of the thermoMETER CTLaserGLASS marks the real spot location and spot size up from 1mm at any distance. The 70:1 (or 45:1) optics with selectable focus provide a very small spot size of just 1mm. ThermoMETER CTLaserGLASS has a stainless steel sensor head and can be used in ambient temperatures of up to 85°C without cooling and to protect the laser aiming optics has an automatic laser switch off at 50°C. Cooling and protection accessories are available for harsh environmental conditions. For example, a water-cooled version for ambient temperatures of up to 175°C.


INDUSTRIAL APPLICATIONS Micro-Epsilon’s thermoMETER CT series of compact, inline (fixed) infrared temperature sensors are suitable for use in industrial applications from maintenance and process monitoring tasks to R&D and test laboratories. The series operates with specific wavelengths and is suitable for measuring the temperature of most materials.


Micro-Epsilon T: 0151 355 6070 www.micro-epsilon.co.uk


/ FACTORYEQUIPMENT


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