Abstract

A pyrometer system for the measurement of the temperature of a primary source of heat which might be contaminated by radiation from a transient spurious source of heat at a higher temperature, and in which the presence of radiation from the spurious source can be detected or identified by spectral discrimination. The received radiation is separated into two spectral components of which a second component comprises a significantly higher proportion of radiation emitted by the spurious source than does the first component. The ratio of, or the difference between, the magnitudes of the radiation in the second and first components is used to identify or detect the presence of spurious radiation and to produce an error, or flag, signal which is used to inhibit operation of the pyrometer or to cause it to hold the last received `good` reading before the occurrence of the spurious radiation.