Abstract: A pyrometer system for a gas-turbine engine, or the like, has a high-resolution radiation pyrometer that supplies signals to a detector unit. The detector unit includes an inverter that inverts the pyrometer output and supplies these signals via a diode to one electrode of a capacitor. The other electrode of the capacitor is grounded, a resistor being connected across the capacitor so that it is slowly discharged. The charge on the capacitor approximately follows the high-value/low-temperature signals, which are reinverted by a processing unit to give an averaged temperature indication. The diode is short-circuited for periods, approximately equal to the blade rotational frequency. During these periods the charge on the capacitor drops to the instantaneous value of the pyrometer output, producing a low-voltage/high-temperature spike. The detector unit includes a store to which these spikes are supplied after reinversion.