Abstract: A radiation thermometer comprises an optical objective through which radiation to be detected passes. A beam splitter has a central region through which a central portion of the radiation which has passed through the objective passes undeflected and an outer region which reflects radiation surrounding the central portion. An eye piece receives radiation passing through the beam splitter; and a radiation detector receives radiation reflected by the beam splitter.

Abstract: A purge assembly for mounting to a radiation thermometer, comprises a purge tube for mounting in front of the radiation thermometer. At least two axially spaced chambers are positioned about the purge tube, each pair of chambers being linked by a respective restrictive opening such that a difference in pressure exists between adjacent chambers in use. An upstream chamber with respect to the flow of purge fluid is connected to source of purge fluid such as air in use and a downstream chamber with respect to the flow of purge fluid opens into the purge tube via a swirl reducing system whereby purge fluid is emitted into the purge tube in use. The chambers are positioned such that fluid flows through the chambers generally towards the lens and then through the downstream chamber opening towards an outer end of the purge tube away from the lens.

Abstract: Method and apparatus for monitoring the quality of a weld performed with an electrode mounted on an automatically controlled electrode support arm which moves between a rest position and a series of spaced operative positions in each of which a weld operation is performed. The apparatus includes a radiation detector for connection to a monitoring system and a radiation collector attached to the support arm adjacent the electrode and coupled to the radiation detector by optical fibers to receive in use a first level of radiation from electrode and a second level of radiation from the weld zone when the arm is in its operative position. A reference source of radiation is also provided that is located such that when the support arm is in its rest position, the collector receives a third level of radiation from the reference source, whereby the radiation detector generates three signals corresponding to the three levels of radiation impinging on the detector for supply to the monitoring system.