Before the use of low emissivity glass it was relatively easy to measure the temperature of the glass as it exited the Glass Tempering oven by using a 5µm waveband thermal linescanner.

Low emissivity glass, sometimes referred to as soft coated Low E glass is coated on one side. It is processed through a tempering/toughening oven with the soft coated side up to prevent damage to the coated side from the support rolls underneath. This makes measuring the glass surface temperature with a top mounted linescanner almost impossible. There are many grades of low emissivity coated glass and their emissivity values are very low and each grade has a different emissivity value.

There simply isn't enough room under the glass to mount a scanner to view the uncoated underside. A solution had to be found.

Solution

Using a LAND LSP-HD 50 infrared linescanner scanning from above is supplemented by a secondary sensor under the line. This sensor is usually a LAND Solonet 5 (SN5) with laser alignment. The Solonet is positioned to measure a narrow stripe along the underside of the glass. The location of this stripe is matched to a compensation zone for the LSP-HD 50 scanner above. The LSP-HD 50 temperature profile is amplified to match the underside temperature from the SN5. The remaining profile is amplified by the same percentage to achieve a fully corrected thermal image of the low emissivity coated glass.

Result

This customer has stated that their production of high quality tempered low emissivity glass has increased significantly.

The key advantages of this measurement are:

• The customer makes products right the first time  - more products can be made in a day
• Visual distortion, caused by uneven tempering in some windows is eliminated. (this is very important in many buildings where the windows go from floor to ceiling - as you look upwards and downwards through a badly tempered window the scene will distort making you feel dizzy - this can be very bad in a large office environment).
• Profits increase.
• The customer can demonstrate low distortion windows to potential customers.

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