| 摘要 |
<p>1,268,453. Acoustic thermometer. GENERAL ELECTRIC CO. 24 Sept., 1969 [17 Oct., 1968], No. 46911/69. Heading H4D. In a system for sensing the temperature T of a region by detecting the phase shift # of a fluid pressure wave signal in being transmitted through a sensor tube disposed in a medium in the region, fluidic devices are used for the signal generation and phase shift detection and the fluid in the tube is isolated from the medium to avoid contamination by the medium. In the Fig. 1 embodiment fluidic oscillator 15 and amplifier 16 superimpose an oscillatory component on the steady pressure provided by source 12 for the fluid (e.g. air or water) in sensor tube 10. Tube 11 acts as a pre-heater for the fluid. The single-ended pressure signal at the output 18 of tube 10 is converted to a pushpull signal at the output of amplifier 22 by passing it to the control jets of amplifier 22 via resistance 25 and a low-pass filter (resistance 26 plus capacitance 27) respectively. The phase shift detector, 17, comprises rectifiers 20, 21 each receiving at its control jets the input pressure signal of tube 10 and the push-pull signal from one receiver of amplifier 22. Low-pass filters 23, 24 smooth the rectifier outputs to give a differential output pressure #P o dependent on the phase shift. The rectifiers are such that #P o has a null for # = n#/2 (n = 1, 3, 5 ...) and the sensor tube length and oscillator frequency are selected such that there is a null at some reference temperature, i.e. their selection determines n. #P o then represents the deviation of T from the reference temperature. By selecting a high value of n, the apparatus sensitivity d#/dT is increased, but at the expense of useful temperature range (since # must be less than 180 degrees to avoid ambiguity). To overcome this a dual-mode system, Fig. 7, is arranged to operate normally at high-n but to switch to low-n operation if the temperature deviation exceeds a predetermined limit. The high-n operation is provided by oscillator 15b and phase shift detector 17b, the low-n operation by oscillator 15a and phase shift detector 17a. Amplifier 70 or 74 is enabled to pass an output to summing amplifier 73 according to the state of a switch 76 which compares detector 17a output with a threshold set by a pressure P B and switches on amplifier 70 only when the threshold is exceeded, i.e. when there is a large temperature deviation. In alternative dual-mode systems (a) the low-n mode is provided by a Helmholtz oscillator whose frequency is a function of the sensed temperature and this frequency is compared with a fixed high-n mode frequency to determine if the temperature deviation exceeds the predetermined limit (Fig. 8, not shown) or (b) a single oscillator is used to excite two sensor tubes of different length (not shown).</p> |
