even more so if gamma thermometers should replace neutron monitors as the primary means of measuring reactor power in pwr 39 s in the preferred embodiment previously described the extra thermocouple junction denoted as t mid serves to provide a reference temperature for comparison with t hot and t cold in an alternate embodiment an external reference temperature that of the reactor coolant may be utilized this is shown schematically in fig7 where a third electrical lead is added to a conventional gamma thermometer thermocouple assembly at tc 1 so that in addition to the differential voltage of the two thermocouples an absolute voltage of one of the thermocouples is obtained the thermocouples are then located as in a conventional gamma thermometer in the embodiment shown in fig7 an alumel lead is added to a chromel alumel thermocouple to obtain the temperature of the thermocouple tc 1 junction the signal processor shown in fig7 consists of logic devices that combine the two thermocouple voltages together with a voltage v c indicative of the core exiting coolant temperature to produce the signal ratio r 2 given by equ4 which is indicative of t 2 t c t 1 t c in this equation r is directly related.