the amplifier 28 filter 30 or filters and multiplier 32 into a dc equivalent signal that represents the rms noise developed in the tuned circuit 24 which is proportional to the absolute temperature of the sensor 12 this processor noise signal depends on the temperature and the components in the first or preamplifier stage of the signal processor 16 the equivalent noise resistance enr and the temperature of the preamplifier determine the noise contribution of the signal processor 16 the inductors l 2 capacitor c and the preamplifier 26 are all contained in a common isothermal enclosure 34 whose temperature is controlled and is measured using an ordinary thermistor or semiconductor temperature sensor the input section of the noise signal processor 16 contains three remotely actuated switches or relays s1 and s2 that are actuated by relay command signals issuing from the controller 18 these switches which may be called 34 crowbar 34 switches may be actuated to short out s2 either or both sections of the split inductor l 2 or the sensing resistor s1 to produce up to eight different circuit configurations not all of which are independent that provide different noise voltage signals to the input of the differential preamplifier which can then be analyzed to separate the noise signal contributions of the sensor and the preamplifier the switches permit the noise signal output to be measured under at least the following circuit configurations 1 with all switches open the sensor noise temperature in the rlc circuit configuration 2 with the sensor shorted the contributions of the inductor.