Measuring thermocouple time constants: a new method

The author describes a new method of measuring the instantaneous time constant using two thermocouples rather than one. Previously such an approach was proposed by Strahle and Muthukrishnan. He demonstrates that the use of the cross power spectrum and the auto power spectra of the signals delivered by two thermocouples submitted to the same physical conditions allows the calculation of the mean time constants of these thermocouples. Using this approach, it is possible to calculate first this ratio and then the time constants. The compensation of the thermal inertia of the thermocouples is then a straightforward operation which allows the calculation of the real fluctuations of the temperature.