| 摘要 |
1. An arrangement for the continuous determination of physical properties of fluids, especially of the flow rate thereof, comprising a heatable temperature sensor (2, 15) which is exposed to the fluid, and consists of an electrical heating resistor and of an oscillating crystal coupled thermally to the heating resistor and having a temperature-dependent natural frequency, and a digitally operating evaluating device to which, as an essential input variable, a digital signal derived from the oscillating frequency of the oscillating crystal is fed, wherein the difference in the oscillating frequencies is a direct measurement of the property to be measured, especially the flow velocity, which is a function of the heat output of the heatable oscillating crystal to the fluid, characterized in that the heating resistor and the oscillating crystal are coupled thermally in such a manner that both have essentially the same temperature, a second oscillating crystal (1, 13) with a temperature-dependent natural frequency serving as a reference sensor for compensation of the fluid temperature is provided, and is also exposed to the fluid, the difference between the oscillating frequencies of the two oscillating crystals and a digital signal representing the heat output fed to the heating resistor in each case are applied as essential input variables to the evaluating facility (6-10, 8-20), the heat output is regulated to a constant value and the oscillating crystals have the same temperature-dependent frequency response.
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