New thin-film multijunction thermal converters with negligible low frequency AC-DC transfer differences

Abstract

The AC-DC transfer differences of thin-film thermal converters at low frequencies are caused by nonlinearities in the heat transport mechanisms and in the thermal-to-electric conversion process. The resulting power coefficient of the sensitivity has been compensated by adding another nonlinear temperature sensitive component to the thermal-to-electric conversion process. This is a thin-film Ni resistor mounted under the thermocouples and connected to the output of the thermocouples. The Ni resistor together with the internal resistance of the thermocouples forms a resistive divider for the output voltage. The positive temperature coefficient of the Ni resistor in the divider compensates for the negative power coefficient of the sensitivity. As a result, converters used at a rated voltage of 1.5 V or a rated current of 7 mA have an AC-DC transfer difference below 0.3 /spl mu/V/V and 0.3 /spl mu/A/A respectively with a standard uncertainty of 0.3 /spl mu/V/V and 0.3 /spl mu/A/A respectively at a frequency of 10 Hz.