Apparatus for simultaneous temperature and heat-flow measurements under transient conditions

Abstract

In this paper, it is shown how a heat-flow transducer and a digital electronic unit can be used together for simultaneous measurements of heat flow and temperature. The electrical output of the sensor consists of a voltage generator (whose open circuit voltage is proportional to the rate of the heat flow to be measured). The electrical output of the sensor acts as a single battery and metallic resistors were disposed between the terminals. The open circuit voltage is proportional to the rate of heat flow to be measured. The value of the resistor is controlled by temperature. The procedure for simultaneously measuring heat flow and temperature is made straightforward by including a balanced Wheatstone bridge driven by an ac carrier as an integral part of the design. To solve the difficult problem of precise detection and maintenance of the balance, the classical Wheatstone bridge configuration has been slightly modified by adding a capacitor to smooth the phase variations around the balance. The discrete time feedback loop used for automatically balancing the bridge includes a digital integrator which sums the phase errors and provides the required voltage. As a result, temperature measurements were made with a linearity better than 1% in the measuring range and the digital readout is obtained with a rise time of 10 ms.