FLUIDIC TEMPERATURE SENSOR AND ITS USE

Abstract: A temperature sensor comprises a pneumatic fluidic bistable amplifier (16) whose control ports (26, 28) are interconnected by a tube (34) to form a fluidic oscillator. The tube (34) is exposed externally to a hot gas stream, such as the turbine inlet gases in a gas turbine engine, so that the speed of sound in the tube (34) varies with variations in the temperature of the gases. This results in a corresponding variation in the oscillation frequency. The signal from the oscillator (16) is then amplified by a fluidic buffer amplifier (42) and converted to an electrical frequency signal by a transducer (62).

Description: "PLUIDIC TEMPERATURE SENSORn Field of the invention This invention relates to temperature sensors, and particularly but not exclusively to sensors for sensing the turbine inlet temperatures in gas turbine engines. It is desirable to have a signal representative of turbine inlet temperature so that the fuel control system can supply the right quantity of fuel to keep the turbine inlet temperature at the maximum permissible, and thereby obtain the best performance from the engine. Such sensors may be required to operate at temperatures as high as 11000C. The prior art Previously-proposed sensors for this purpose have used thermoelectric devices which either are limited in life by the relatively low operating temperature capability of the materialsbecause of oxidation and corrosion problems in hot gas atmospheres or are extremely costly due to the use of noble elements in their construction. Also, these previously-proposed sensors measure temperature at what is virtually a point, rather than over a greater area, so that the measured temperature may not be truly representative of the gas stream. Summary of the invention According to the X sent invention, a temperature sensor is characterised a fluidic oscillator whose oscillation depends on the propagation of pressure waves through a space, the space being constructed to maintain the fluid therein at a temperature related to the temperature to be sensed, whereby the propagation time of a pressure wave through the space and hence the frequency of the oscillator is dependent on the temperature to be sensed. More specifically, in the preferred embodiment, the fluidic oscillator comprises a fluidic bistable amplifier having a jet nozzle, a pair of opposed control ports for deflecting the Jet produced by the nozzle, and a plurality of outlet ports for receiving the Jet, the control ports being interconnected by a passage, switching of the Jet from one outlet port to another to produce the oscillation being effected by a pressure wave propagating through the passage from one control port to the other. The passage may be constituted by a tube exposed externally to a fluid, such as the combustion gases supplied to the turbine of a gas turbine engine, whose temperature is to be measured. Such a construction provides measurement of the gas temperature over an extended area, and may allow the use of noble metals to be avoided. The temperature sensor may also include buffering means, such as a fluidic buffer amplifier, for receiving the output signals from the oscillator and providing output signals at the same frequency as the oscillator; preferably, the buffering means is situated close to the fluidic oscillator. Such an arrangement allows the fluidic frequency signals to be transmitted to a remote location, without the impedance variations which may occur in long connecting conduits affecting the oscillator; this may be important because of the sensitivity of fluidic oscillators to impedance variations. Where the fuel control system of the gas turbine engine is electronic in operation, an electrical signal representative of temperature will be required, and this can be provided by a transducer receiving the output signals from the fluidic oscillator. Where a buffer amplifier is provided close to the fluidic oscillator, the transducer can then without difficulty be positioned remote from the fluidic oscillator, and receive the fluidic frequency signals from the buffer amplifier. Description of the preferred embodiment Figure 1 is a schematic block diagram of a fluidic temperature sensor embodying the present invention; Figure 2 is a schematic structural view of a fluidic bistable amplifier used in the sensor of Figure 1; and Figure 3 is a graphical representation of a atypical frequency versus temperature characteristic for a sensor of the type shown in Figure 1. Referring first to Figure 1, the temperature sensor embodying the invention is indicated by the reference numeral 10, and is arranged to sense the temperature of a fluid flowing in a conduit 33. In essence, the temperature sensor comprises a first fluidic bistable amplifier 16, which is connected in a self-oscillating configuration, to oscillate at a frequency which is dependent on the temperature of the fluid in the conduit 33. The output signals from the amplifier 16 are amplified by a fluidic buffer amplifier 42, and the resulting amplified signals are converted into electrical signals by a piezoelectric ceramic transducer 62. These electrical signals constitute the output of the sensor and can be used, for example, for instrumentation or for control purposes. The fluidic amplifiers 16 and 42 have pressure supply ports 14 and 48, respectively, which are supplied with pressurised fluid, such as air,- from a supply 12, which will in many cases be a compressor. The supply port 14 leads the gas to a jet-forming nozzle 20, which directs a Jet of gas into an interaction chamber 18 (see Figure 2j. The interaction chamber 18 has side walls 22 and 24; in operation, the get from the nozzle 20 will tend to attach itself to one of the side walls 22 and 24. Adjacent- the nozzle 20, control ports 26 and 28 open into the interaction chamber 18, through the side walls 22 and 24 respectively. These control ports are interconnected by a tube 34 which is situated in the conduit 33; the tube 34 acts as a heat exchanger; the configuration of the tube 34 provides a large surface area for the transfer of heat from the fluid in the conduit 33 to the fluid inside the tube 34, so that the temperature of the latter fluid is closely representative of the temperature of the fluid in the conduit 33, but without any actual communication between the two fluids. If, for example, the jet from the nozzle 20 attaches itself to the side wall 22, the jet will tend to aspirate fluid from the control port 26 formed in that side wall. Thus, from the time when this- attach- ment occurs, a low pressure wave is transmitted from the control port 26 into the tube 34. This wave propagates through the tube 34; when the wave reaches the control port 28, it acts on the main jet from the nozzle 20, to pull the main Jet towards the side wall 24. The transient energy of the low pressure wave is sufficient to overcome the force holding the main Jet to the side wall 22, so that the Jet now switches over and attaches itself to the side wall 24. The sequence of events described above now repeats itself, but with the low pressure wave travelling in the opposite direction through the tube 34. Thus, the Jet from the nozzle 20 will oscillate between the two side walls 22 and 24. The delay time between successive switchings of the jet is determined by the length of the tube 34 and by the speed of sound prevailing in the fluid in this tube; this speed is dependent on the temperature of the fluid, and hence on the temperature of the fluid flowing in the conduit 33. The delay time determines the frequency of oscillation; assuming that the fluidic amplifier 16 operates with a gas, this frequency is given by the formula: EMI6.1 where f = the frequency of oscillation T = the absolute gas temperature L = the length of the feedback passage y = ratio of specific heats of the gas g = gravitational constant R = characteristic gas constant. Since y, g, R and L are constants, the frequency of oscillation is uniquely related to the square root of the temperature of the gas within the tube 34. The downstream part of the interaction chamber 18 has outlet passages 30 and 32, which receive the main Jet alternately, depending on whether the Jet is attached to the side wall 22 or to the side wall 24. The outlets 30 and 32 are separated by a blunt splitter 36; each outlet passage has a vortex vent 38 or 40, which prevent reflected waves from the outlets from influencing conditions in the interaction chamber 18, where such influence might interfere with the basic switching function of the main Jet and cause unsteady oscillation. The outlets from the amplifier 16 are connected by conduits 58 and 68 to control ports 50 and 52 of the buffer amplif er 42; the amplifier 42 also has an interaction chamber 44, into which the fluid supplied by the supply port 48 is directed as a jet by a nozzle 46, and which has in its downstream portion two outlets, which are connected to the transducer 62 by conduits 54 and 56. Thus, the jet from the nozzle 46 will be deflected towards one or other of the outlets by the sils applied to the control ports 50 and 52. The function of the buffer amplifier 42 is to isolate the bistable amplifier 16 from the effects of load impedance variations in the transducer 62 or in the conduits 54 and 56 and to amplify the signals from the amplifier 16. The pulsating signal from the buffer amplifier 42 is applied to ±he- piezo- electric transducer 62, which converts the signal to an electrical frequency proportional to the square root of the gas temperature being sensed. This electrical frequency is delivered from the transducer 62 for either instrumentation or control purposes.

Claims: CLAIMS 1. A temperature sensor, characterised by a fluidic oscillator (16) whose oscillation depends on the propagation of pressure waves through a space (34), the space (34) being constructed to maintain the fluid therein at a temperature related to the temperature to be sensed, whereby the propagation time of a pressure wave through the space (34) and hence the frequency of the oscillator (16) is dependent on the temperature to be sensed. 2. A temperature sensor as claimed in Claim 1, in which the fluidic oscillator comprises a fluidic bistable amplifier (16) having a jet nozzle (20), a pair of opposed control ports (26, 28) for deflecting the Jet produced by the nozzle, and a plurality of outlet ports (30, 32) for receiving the jet, the control ports (26, 28) being interconnected by a passage (34), switching of the jet from one outlet port (30, 32) to another to produce the oscillation being effected by a pressure wave propagating through the passage (34) from one control port to the other. 3. A temperature sensor as claimed in Claim 2, in which the passage (34) is constituted by a tube exposed externally to a fluid whose temperature is to be sensed. 4. A temperature sensor as claimed in Claim 3, in which there is no fluid communication between the fluid in the tube (34) and the fluid whose temperature is to be sensed. 5. A temperature sensor as claimed in any of the preceding claims, which is used to measure the temperature of combustion gases supplied to the turbine of a gas turbine engine. 6. A temperature sensor as claimed in any of the preceding claims,in which the signalsfrom the oscillator (16) are converted by a transducer (62) into electrical signals of the same frequency. 7. A temperature sensor as claimed in any of the preceding claims, which includes a fluidic buffer amplifier (42) for amplifying the output signals from the oscillator (16). 8. A temperature sensor as claimed in any of the preceding claims, in which the fluidic oscillator (16) operates on a supply of pressurised gas such as compressed air. 9. A fluidic temperature sensor, including a fluidic oscillator (16), whose frequency of oscillation is indicative of the temperature to be sensed, characterised by a fluidic buffer amplifier (42) connected to be controlled by the outputs (30, 32) of the oscillator (16), and providing outputs (54, 56) at the oscillator frequency, which outputs are connected to a fluidpressure to electrical transducer (62) which provides an electrical signal indicative of the temperature to be sensed. 10. A temperature sensor as claimed in Claim 9, in which the buffer amplifier (42) is situated close to the fluidic oscillator (16), while the transducer (62) is situated remote from the oscillator (16) and buffer amplifier (42).

Inventors: MCCARTY, ROBERT S., SUTTON, TREVOR G.
Applicants: THE GARRETT CORPORATION
Application year: 1980
Main classification: G01K11
IPC codes: G01K11, G01K13, F15C1