Improving the accuracy of thermocouple temperature measuring circuits

The voltage measurement accuracy in thermocouple circuits used for air/gas temperature measurements in gas turbine aero engines is discussed. A circuit composed of three sections of different cable materials is considered. The voltage output is produced by the addition of three thermocouple voltages. A floating reference junction, where the temperature is measured by a resistance thermometer, is used. The thermal plane is a commercially available uniform temperature reference box with a capacity of 60 thermocouple channels. Readout is by on-line computer. The equivalent resultant accuracy is 0.5 deg up to 480 deg. The use of connectors and sliprings in thermocouple circuits is also discussed.