Circuit arrangement for measuring low thermal powers

摘要

An electronic calorimeter is intended to permit efficiencies, flow rates and thermal conductivities to be determined by measuring low thermal powers. According to Fig. 1, a temperature-dependent resistor (11), (e.g. PTC resistor) is situated in a bridge circuit and is heated up by the bridge current. By controlling the bridge current, a controller (16) keeps the bridge in balance and thus maintains the temperature of the PTC resistor (11) constant via the ambient temperature. The electric power converted in the process in the PTC resistor (11) is determined in a multiplier (18) by current and voltage measurement (I, U). When the PTC resistor (11) is brought into thermal contact with a heat source or heat sink (12), this converted electric power (P) varies precisely by the value of the thermal power absorbed or released, i.e. the thermal power is compensated for by an electric power if measurement is made in each case in equilibrium (in the steady state). The compensated thermal power can be used to measure efficiencies or quantum efficiencies of opto-electronic and Peltier components as well as of laser crystals, or else thermal conductivities and flow rates of fluids. <IMAGE>