GB1591216A

GB1591216A - Fluid flow speed indicator systems

Info

Publication number: GB1591216A
Application number: GB1958178A
Authority: GB
Original assignee: ML Aviation Ltd
Current assignee: ML Aviation Ltd
Priority date: 1978-05-15
Filing date: 1978-05-15
Publication date: 1981-06-17
Also published as: DE2914778A1

Description

(54) FLUID FLOW SPEED INDICATOR SYSTEMS (71) We, M.L. AVIATION COMPANY LIMITED, a British Company, of M.L. Building, Ajax Avenue, Trading Estate, Slough SL1 4BQ, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to indicator systems for use in indicating the speed of movement of a body in air or other fluid, such as water, or for use in indicating the speed of movement of such fluids past a stationary sensing position.

According to the invention, an indicator system comprises means to produce a burst of ionisation at a point in a fluid flow: means at a preset distance downstream of the ionisation producing means to sense the arrival of the ionisation burst; and means to monitor the time elapsing between the production and the arrival of said burst and thereby to indicate the speed of passage of said burst, wherein the time monitoring means comprises a clock pulse generator; a counter coupled to the clock pulse generator and operative to start to count the clock pulses from the instant of production of the ionisation burst; means to stop the count on arrival of the burst; means to store counts for a succession of said bursts; and a comparator to compare each count with at least one of the counts previously stored in the storage means and to inhibit indication of the speed if-the compared counts differ by more than a predetermined amount.

By "fluid flow" is meant a unidirectional relative movement between a fluid and the ionisation producing and sensing means.

Hence, either the fluid can move past the ionisation producing means and the sensing means in that order, or those means can move together in a substantially stationary fluid, the ionisation producing means preceding the sensing means in the direction of movement.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a schematic block diagram of one form of indicator system in accordince with the invention, Figs. 2 and 3 show alternative ionisation electrode and detector arrangements, Fig. 4 is a schematic block diagram of an indicating system incorporating a phaselocked loop, Fig. 5 is a schematic block diagram of a system for indicating both the air speed of an aircraft and the corresponding Mach number Fig. 6 is a schematic diagram of an ionisa tion electrode and detector arrangement for indicating both the speed and the direction of fluid flow, and Fig. 7 is a schematic underneath plan of an aircraft, illustrating the use of two indi cators in accordance with the invention for - monitoring the yaw of the aircraft.

Referring to Fig. 1, an air flow speed indi cating system includes a spark gap 1 which is connected to the secondary winding 2 of a pulse transformer 3. The primary winding 4 of the transformer is connected to a pulse generator 5, which at predetermined time intervals generates short, high voltage pulses, causing breakdown of the spark gap 1 and ionisation of the air in the region of the gap.

The spark gap is sited in an air flow, the direction of which is indicated by an arrow 6. The pocket of ionised air therefore moves in the direction of the arrow.

Downstream of the spark gap 1 in the air flow is positioned an ionisation detector 7 comprising two grids 8 and 9. The grid 8 comprises a group of. spaced-apart vertical wires, whilst the grid 9 comprises a similar group of horizontal wires.

The grids are connected to the inverting and non-inverting inputs, respectively, of a differential amplifier 10. A reference vol tage is applied to the detector from a posi tive source 11.

When the pocket of ionised air reaches the detector grids, a current will flow bet ween the grids, and the resulting signal will cause an output to be produced by the amp lifier 10. This output is fed to the STOP input of a counter 12.

Each pulse generated by the generator 5 is also fed to a START input of the counter 12. Extremely accurately timed clock pulses are fed to the counter 12 from a crystal controlled clock generator 13. The counter is started by a pulse from the generator 5 and counts the clock pulses until the counting is stopped on receipt of the pocket of air which has been ionised by generation of the pulse which started the count.

The fixed distance between the spark gap l and the detector 7 is accurately known.

This distance may for example, be in the range of 4 to 12 inches. The time taken for the ionised air to travel this fixed distance is determined from the clock pulse count.

Hence, the speed of the air flow can be accurately calculated by a speed calculator 14 and displayed, if desired, on a display 15.

The count is also fed from the counter 12 to a memory 16 and to a comparator 17.

Each new count is compared in the comparator with the previous count stored in the memory, and if there is an unreasonable difference between the successive counts, clearly not compatible with a normal change in speed, the speed calculation is inhibited for the later count by a signal on a line 18 from the comparator 17.

If the detector system is a.c. coupled, only rates of change of ionisation will be significant, not the absolute levels of ionisation.

The air flow may be current of air which is passing a stationary assembly of the spark gap 1 and the detector 7. Alternatively, the same effect as an air flow can be obtained by moving the spark gap and the detector together, in the opposite direction to the arrow 6, in still air. Hence, the spark gap and the detector can be mounted on the outside of an aircraft in a fore-and-aft line, with the spark gap in front of the detector, to measure the air speed of the aircraft.

The measured air speed is independent of changes in temperature, barometric pressure and humidity.

An unacceptable count, as mentioned above, could result from the aircraft flying through a charged cloud which causes spurious ionisation of the air around the aircraft.

In fact, random counts could then be obtained for many successive pulses generated by the generator 5. It would therefore be necessary for the comparator 17 to compare each count with a memory output representing the normal value of counts occurring prior to the start of the spurious ionisation, and not merely with the immediately preceding count.

In another form of construction, the detector grids 8 and 9 may be made by forming the horizontal and vertical conductors on printed circuit boards. However, it is clearly advantageous for the detector grids to cause as little disturbance of the air flow and as little drag as possible. Hence, alternative forms of detector might be preferable. Such forms might comprise a plate of aerofoil section, or a needle-like electrode. In either case, the adjacent fuselage or wing surface of the aircraft could act as a ground plane serving as the other pole of the detector.

Similarly, instead of using a spark cap as the ionising means, a sharp-edged or aerofoil-section plate or a needle-like electrode could be used to minimise the disturbance of the air and the drag on the aircraft.

Again, the fuselage or wing surface from which the electrode projects could act as the other pole, the ionising voltage being then applied between the aircraft surface and the electrode. In order to reduce the possibility of actuation of the speed calculator and the display by counts which are apparently acceptable but which, in fact, result from the receipt of spurious ionisation, coding of the ionisation bursts can be obtained by arranging three or more ionising electrodes side-by-side, as shown in Fig. 2 of the drawings. In this case the electrodes 19, 20 and 21 are shown as aerofoil-section plates. The electrodes are connected to a pulsing circuit 22 which applies, say, 1000 volts positive and 1000 volts negative to the electrodes 19 and 21, respectively, relative to the centre electrode 20. Three similar detector plates 23, 24 and 25 are aligned with the electrodes 19, 20 and 21, respectively, and are positioned aft of those electrodes. The plates 23, 24 and 25 are connected to one end, a centre tap and the other end, respectively, of a primary winding 26 of a transformer 27. The secondary winding 28 is connected to detection and counting circuitry 29, which can be similar to that in Fig. 1. The electrode 20 and the plate 24 are electrically connected to the fuselage or wing surface on which they are mounted.

Due to the ionising electrode configuration and operating potentials, normally received ionisation will cause the plates 23 and 25 to become positive and negative, respectively, relative to the plate 24. A signal will therefore be induced in the secondary winding and will cause the counter to stop counting the clock pulses, in the same manner as in the Fig. 1 embodiment.

If, however, a spurious ionising force, such as a charged cloud, is encountered, this can produce ionisation of only one polarity relative to the aircraft surface, and hence relative to the central detector plate 24. The plates 23 and 25 will therefore be raised to the same positive or negative potential rela- tive to the plate 24 and no resultant signal will be induced in the transformer secondary winding 28. This unwanted ionisation. will therefore not cause the counter to stop counting the clock pulses.

In an alternative arrangement shown in Fig. 3 of the drawings, the same result can be achieved by using three ionising electrodes 30, 31 and 32, here shown, for the sake of example, as needle-like electrodes, spaced apart along a fore-and-aft line, with a single detector electrode 33 aligned therewith. The ionising electrodes are connected to a circuit 34, similar to the circuit 22 of Fig. 2, which applies opposite potentials to the electrodes 30 and 32 relative to the electrode 31. Due to the relative displacement of these electrodes, two successive bursts of ionisation of opposite polarities will be received by the detector electrode 33. The signals fed by the electrode 33 to a detection and counting circuit 35 will therefore comprise a pulse of one polarity followed fy a pulse of the opposite polarity. Receipt of the correct pulse sequence is detected by the circuit 35 and counting of the clock pulses is stopped.

If spurious ionisation is caused, for example by a cloud as mentioned previously, this will be of only one polarity and the resulting signal fed to the circuit 35 will not satisfy the reversed polarity pulse sequence criterion.

The spurious ionization will therefore be ignored.

In an alternative system, not specifically illustrated in the drawings, the same effect can be achieved by using a single ionising electrode arrangement and applying- to the electrode a sequence of pulses of alternately reversed polarity, either immediately following each other or with gaps therebetween. The detection circuit could then include a zero-crossing detector or other circuitry to determine whether the correct sequence of pulses has been received.

Referring to Fig. 4 of the drawings, the ionisation electrode(s), represented by a box 36, and the detector electrode(s), represented by a box 37, can be connected in a self-regenerative phase-locked loop including the ionising pulse generator 38 and a phase discriminator 39. Any change in phase of the signal received at the detector electrode 37 due to a change in air speed will be counteracted by a change in frequency of the pulses generated by the generator 38, so that the frequency becomes a measure of the air speed.

Fig. 5 of the drawings illustrates an air sped detector which can be similar to any of those described abovej but including means to provide an indication of Mach number. In this case a spark gap 40 is used as the ionising means, and the ionising pulse generator 41 is driven by a ramp generator 42 which causes the pulse generator to produce pulses which increase in magnitude so that each pulse first causes ionisation of the air at the spark gap, followed by breakdown and arcing across the gap.

The arcing generates sound waves which may be in the audible range, or ultrasonic, or a combination of both, and which are picked up by a receiving transducer 43, mounted adjacent the ionisation detector 44. Two signals are therefore fed to a detection and calculating circuit 45, namely the ionisation pulse signal which indicates the air speed of the aircraft, and a signal which is dependent upon the speed of the sound waves through the atmosphere which is actually prevailing at the aircraft. From these two signals the circuit 45 calculates the Mach number as well as the air speed and feeds both values to a display 46. The transducer 43 can be mounted flush with the surface of the aircraft in order to minimise disturbance with the air flow.

If the air temperature is measured, this information together with the measured velocity of the sound waves can be used for other navigational purposes.

In Fig. 6 of the drawings is shown an arrangement wherein a single ionisation means 47 is encircled by a ring of ionisation detectors 48. The ring may be, for example, 12 inches diameter. This arrangement, in combination with an ionisation pulse generator and detection and calculation circuitry (not shown) can be used in a stationary installation to indicate not only the speed of air flow but also the direction of the flow. By scanning the detectors in synchronism with the generation of the ionisation pulses (though not necessarily allowing only one pulse period per detector) and by allowing time for the ionisation to reach the detectors before moving to the next detector, the direction is determined from which of the detectors receives the ionisation. In the figure sixteen detectors are shown, one for each of sixteen points of the compass, but any required number may be provided.

Again, the indicated direction and speed may relate to actual air flow, or to aircraft or other vehiclular movement relative to still air.

In an alternative arrangement, a single detector may be provided at the centre, encircled by a ring of ionisation electrodes which are pulsed in sequence. Alternatively, the single central detector or ionisation electrode may be rotated to point at each of the encircling electrodes in turn.

Referring to Fig. 7 of the drawings, the yaw of an aircraft can be determined by providing two ionisation and detector electrode pairs 49 and 50, one adjacent each wing tip, with a common ionisation pulse generator 51 and detector circuit 52. Any difference between the air speed values obtained from the two pairs will indicate the yaw rate of the aircraft.

Any of the embodiments described above could alternatively be used for determining the speed of flow of other fluids besides air, or the speed of a body moving through such other fluid. For example, in a conductive fluid such as water, a low voltage, high current pulse would cause ionisation of the water and the speed of receipt of this ionisation could be detected by suitable circuitry.

The method could also be used in nonconductive fluids, wherein an ionised dielectric region could be produced in the fluid, the charge on the region being subsequently detected at the detector electrodes.

In any of the arrangements, ionisation of the fluid could be enhanced by providing a radioactive trace element, such as thorium, adjacent the ionisation electrodes. Such element emits a particles which cause the fluid to ionise more readily.

Ionisation of the fluid may be brought about by flashes of ionising radiation, such as ultra-violet light, instead of, or in addition to, the high voltage pulses used in the embodiments described above.

Alternatively, ionisation of the fluid may be caused by an intense ultrasonic signal from a transducer. In this case, and in the case of ionisation by ultra-violet light, the intensity of the ionising energy may be enhanced by the use of parabolic or concave reflecting surfaces.

WHAT WE CLAIM IS: 1. An indicator system, comprising means to produce a burst of ionisation at a point in a fluid flow; means at a present distance downstream of the ionisation producing means to sense the arrival of the ionisation burst; and means to monitor the time elapsing between the production and the arrival of said burst and thereby to indicate the speed of passage of said burst, wherein the time monitoring means comprises a clock pulse generator; a counted coupled to the clock pulse generator and operative to start to count the clock pulses from the instant of production of the ionisation burst; means to stop the count on arrival of the burst; means to store counts for a succession of said bursts; and a comparator to compare each count with at least one of the counts previously stored in the storage means and to inhibit indication of the speed if the compared counts differ by more than a predetermined amount.

2. A system as claimed in Claim 1, wherein the ionisation burst producing means comprises three ionisation electrodes substantially aligned in a direction perpendicular to the direction of fluid flow, and means to apply respective positive and negative ionising potentials to the outer electrodes with respect to the central electrode; wherein the means to sense the arrival of the ionisation burst comprises three detector electrodes substantially aligned with the ionisation electrodes; and wherein the elapsed time monitoring means includes means to sense whether on arrival of the ionisation burst the outer detector electrodes attain opposite polarity potentials relative to the central detector electrode and to inhibit the indication of the speed if they do not.

3. A system as claimed in Claim 2, wherein the polarity sensing means comprises a transformer having a centre-tapped primary winding, the ends of the winding being connected to the outer detector electrodes and the centre tap being connected to the central detector electrode.

4. A system as claimed in Claim 1, wherein the ionisation burst producing means comprises three ionisation electrodes spaced apart along the direction of the fluid flow, and means to apply respectively positive and negative ionising potentials to the two outer electrodes with respect to the central electrode; wherein the means to sense the arrival of the ionisation burst comprises a detector electrode system having two parts between which the received ionisation causes an electric current flow; and wherein the elapsed time monitoring means includes means to sense whether the received ionisation causes a current flow in one direction followed by a current flow in the opposite direction and to inhibit the indication of the speed if it does not.

5. A system as claimed in Claim 1, wherein the ionisation burst producing means includes an ionising voltage pulse generator which produces a train of pulses at predetermined intervals; wherein the ionisation burst producing and sensing means are connected in a phase-locked loop which senses any change in the phase of successive received bursts and corrects the phase by adjustment of the frequency of the ionising voltage pulses.

6. A system as claimed in Claim 1, wherein the ionisation burst producing means comprises a spark gap and a pulse generator to apply voltage pulses to the spark gap to cause arcing across the gap; the system further including a transducer arranged to receive sound waves generated by the arcing; and means responsive to the elapsed time between transmission and receipt of the ultrasonic waves to caluclate the speed of sound in said fluid flow.

7. A system as claimed in Claim 6, for use in measuring aircraft air speed, including means responsive to the calculated speed of sound and to the speed of passage of the ionisation burst to indicate the Mach number corresponding to the speed of the aircraft.

8. A system as claimed in Claim 1, wherein the ionisation burst producing means comprises an ionisation electrode

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Any of the embodiments described above could alternatively be used for determining the speed of flow of other fluids besides air, or the speed of a body moving through such other fluid. For example, in a conductive fluid such as water, a low voltage, high current pulse would cause ionisation of the water and the speed of receipt of this ionisation could be detected by suitable circuitry. The method could also be used in nonconductive fluids, wherein an ionised dielectric region could be produced in the fluid, the charge on the region being subsequently detected at the detector electrodes. In any of the arrangements, ionisation of the fluid could be enhanced by providing a radioactive trace element, such as thorium, adjacent the ionisation electrodes. Such element emits a particles which cause the fluid to ionise more readily. Ionisation of the fluid may be brought about by flashes of ionising radiation, such as ultra-violet light, instead of, or in addition to, the high voltage pulses used in the embodiments described above. Alternatively, ionisation of the fluid may be caused by an intense ultrasonic signal from a transducer. In this case, and in the case of ionisation by ultra-violet light, the intensity of the ionising energy may be enhanced by the use of parabolic or concave reflecting surfaces. WHAT WE CLAIM IS:

1. An indicator system, comprising means to produce a burst of ionisation at a point in a fluid flow; means at a present distance downstream of the ionisation producing means to sense the arrival of the ionisation burst; and means to monitor the time elapsing between the production and the arrival of said burst and thereby to indicate the speed of passage of said burst, wherein the time monitoring means comprises a clock pulse generator; a counted coupled to the clock pulse generator and operative to start to count the clock pulses from the instant of production of the ionisation burst; means to stop the count on arrival of the burst; means to store counts for a succession of said bursts; and a comparator to compare each count with at least one of the counts previously stored in the storage means and to inhibit indication of the speed if the compared counts differ by more than a predetermined amount.

system comprising two parts between which an ionising potential is applied; and wherein the ionisation burst sensing means comprises a plurality of detector electrodes spaced round the ionisiation electrode system, and means to scan the detector electrodes in turn to determine which detector electrode receives the ionisation burst, thereby to determine the direction of the fluid flow relative to the ionisation electrode system.

9. A system as claimed in Claim 1, wherein the ionisation burst sensing means comprises a detector electrode system having two parts between which the received ionisation causes an electric current flow; and wherein the ionisation burst producing means comprises a plurality of ionisation electrodes spaced round the detector electrode system and means to apply an ionising potential to each of the ionisation electrodes in turn; the system further including means to determine which of the ionisation electrodes produces an ionisation burst which is received by the detector electrode system, thereby to determine the direction of the fluid flow relative to the detector electrode system.

10. A system for indicating the yaw of an aircraft, comprising two indicator systems as claimed in Claim 1, wherein the ionisation burst producing and sensing means of one indicator system are located adjacent one wing tip of the aircraft, and said means of the other indicator system are located adjacent the other wing tip of the aircraft; the system further including means responsive to any difference between the speeds of passage of the respective ionisation bursts to indicate yaw.

11. A system as claimed in any one of Claims 1 to 5, 8, 9 or 10, wherein the ionisation burst producing means includes at least one electrode of aerofoil cross section.

12. A system as claimed in any one of Claims 1 to 5, 8, 9, 10 or 11, wherein the ionisation burst sensing means includes at least one electrode of aerofoil cross section.

13. A system as claimed in Claim 1 and substantially as hereinbefore described with reference to the accompanying drawings.