| 摘要 |
<p>28 In the direct measurement of thermal energy transferred in heating or air conditioning installations, a reference voltage is generated across a capacitance connected to one input of an integrating circuit by feedback from the output of the integrating circuit when the voltage across the temperature sensor in one of the outflow or return lines is applied to the other input of the integrator circuit. First and second timing periods initiated by impulses from a volume flow sensor cause successive application of voltages from the other temperature sensor and a constant current source to the other input of the integrator circuit whereupon the integrator circuit charges an integrating capacitance in accordance with a difference between the voltages produced by the temperature sensors during the first timing interval and discharges the integrating capacitance at a constant rate during the second timing interval. A gate is enabled during the second interval to pass clock pulses proportional to the charge on the integrating capacitance. During the first and second timing intervals, a switch in the feedback circuit for the reference capacitance is open.</p> |
