| 摘要 |
<p>1381913 Measuring density electrically ITT INDUSTRIES Inc 30 March 1972 [8 April 1971] 15074/72 Heading G1N A vibration densitometer comprises a probe 10', immersed in a fluid of which the density is required, and having a vane 20' arranged to be vibrated at its resonant frequency, a driver coil 24' actuable to vibrate the vane, a Piezo-electric crystal detector 30' which produces an A.C. signal of which the frequency is equal to that at which the vane is vibrating, the output from the crystal being fed to an input of a tracking filter 91', a control circuit 94' which acts to control the frequency of the pass band of the filter in accordance with the magnitude of the output signal from phase comparator 93' which receives at its inputs signals from the input and output of the filter, the filter also receiving at its input an A.C. signal from an auxiliary oscillator 11, and a power amplifier 92' connected to receive the output signal from the filter and to feed it to control the driver coil, the frequency of which output signal provides a measure on indicator 110' of the fluid density. The oscillator signal amplitude is less than that from differentiator 83' but is sufficient to start the vane vibrating and the oscillator frequency is arranged to be at the midfrequency of the filter pass band.</p> |
