MEASURING SYSTEM INCLUDING THERMAL CONDUCTIVITY DETECTOR MEANS

摘要

A reference thermal conductivity detector and a measuring thermal conductivity detector are connected in different branches of an electrical bridge circuit. The bridge is excited at one power node by a clamped square wave symmetrical about a base voltage line; and the other power node is excited by a feedback circuit sensing the signal at the signal nodes and maintaining the average value of the common mode signal at zero relative to the base line. The output signal taken from the signal nodes is fed to a demodulator circuit for generating an output signal representative of the thermal conductivity of the sample being sensed. Delay circuits are provided for inhibiting the operation of the demodulator during those periods when the polarity of the bridge input power signal is changing.