Land Instruments International has developed two new application specific infrared radiation thermometers for monitoring the temperature of optical fibres during pre-forming and drawing.
The success of both processes depends on precise temperature control, which in practice can be achieved only by non contact methods.
For pre-forming, the company has introduced its new Vapour Deposition Thermometer (VDT), which monitors the temperature of the pre-form as it rotates on the lathe.
The new VDT meets two criteria for successful temperature measurement. VDT has a narrow angle field of view (100:1) which allows it to be sighted precisely on to the pre-form; and it operates at a wavelength of 4.8 to 5.2µm, at which the pre-form is opaque and measurement is unaffected by the burner flames.
Two versions of the thermometer are available; a stand-alone instrument (VDT-U) and a system version (VDT-S).
VDT-S is used with a Landmark Graphic signal processor and is intended for multiple pre-forming lines incorporating up to four thermometers per system.
The temperature measurement range for both versions is 1000 to 2500 degrees C.
At the fibre drawing stage the furnace lining temperature is used as the heating control parameter, which can be measured using the new Fibroptic Drawing Tower Thermometer (DTT).
Suitable for measuring temperatures from 800 to 2600 degrees C, the DTT has an operating wavelength of 1µm and a 4mm measurement spot diameter at the focus distance of 450mm (112:1 FOV), which allows sighting on to the furnace lining.
A 2m long fibre optics light guide facilitates access to the target and enables the detector and electronics enclosure to be located remotely from the furnace.