Abstract
A new and sensitive type of infra-red radiation pyrometer has been designed and constructed, one form of which is specifically designed for measuring the temperature of aluminium extrusions in the 400-500°C range, with reduced dependence on the surface emissivity variations of the material. The basic instrument has two novel features. Firstly, it uses optical negative feedback from a semiconductor lamp to its lead sulphide photocell detector in order to give it overall stability, and secondly it uses an efficient infra-red cut-off filter, a water cell, to improve the power law relationship of received energy to temperature, so reducing the effects of emissivity variation. For the temperature measurement of aluminium and its alloys these variations are reduced to about half those encountered with a normal lead sulphide photocell pyrometer. The basic pyrometer is adaptable from narrow to wide angle working (0.75 in. viewing diameter at 7 ft, upwards) and will cover a range of temperatures from less than 300°C upwards, depending on the optical system. Without water cell filtering the minimum measuring temperature on low emissivity aluminium is less than 70°C.