GB2120384A

GB2120384A - Fluid flow meter

Info

Publication number: GB2120384A
Application number: GB08306925A
Authority: GB
Inventors: Martin Alan Hogbin; Michael Richard Pritchard; Michael John Scott
Original assignee: BESTOBELL
Current assignee: BESTOBELL
Priority date: 1982-05-19
Filing date: 1983-03-14
Publication date: 1983-11-30
Also published as: GB8306925D0

Abstract

A fluidic flow meter comprises a fluidic oscillator having an interaction chamber (1), a main fluid inlet nozzle (2), diverging side walls (3), and control nozzles (4). An ultrasonic transmitter (10) is arranged to transmit a sonic signal across the fluid flow path to a sonic receiver (11) located for receiving the sonic signal after modulation by oscillations in the fluid developed during passage of the fluid through the oscillator. <IMAGE>

Description

SPECIFICATION Fluid flow meter This invention relates to a fluid flow meter of the kind using a fluidic oscillator which produces oscillations when energised by a flow of fluid. The frequency of the oscillation is dependent upon the flow rate of the fluid through the fluidic oscillator and the flow rate of the fluid can be monitored by monitoring the frequency of the generation of the oscillations.

Typically such fluidic oscillators include an interaction chamber with a main fluid inlet nozzle and side walls which diverge from the main fluid inlet nozzle and to which the fluid stream issuing from the nozzle can attach. The interaction chamber also includes control nozzles for exerting fluid pressure on the fluid stream issuing from the main fluid inlet nozzle to direct the fluid stream from one side wall to the other. A splitter is usually provided downstream of the interaction chamber to define the two separate flow paths and the oscillator also includes feedback loops in communication with the diverging side walls downstream of the control nozzles and connected to the control nozzles. Usually the two separate flow paths are brought together downstream of the splitter to issue through a common outlet.The arrangement of the fluidic oscillator including the feedback loops is such that the oscillator self switches cyclically between its two states of flow and this leads to generation of oscillation in, for example, the flow paths on both sides of the splitter, in the feedback loop, and in the common outlet. Oscillations caused by the switching of the fluid stream from one path to the other can also lead to the generation of oscillations in the main fluid inlet.

A fluidic flow meter including such a fluidic oscillator must also include some means of measuring the oscillations which are generated in the fluidic oscillator and this means should preferably not upset the flow conditions through the fluidic oscillator. US Patent Specification 3 690 1 71 describes such a fluidic flow meter and discloses as a method of monitoring the oscillations, the provision of a communicating channel between the flow paths on opposite sides of the splitter with a differential pressure sensing means mounted in this channel to detect differences in pressure on opposite sides of the splitter and hence detect the oscillations generated in the fluidic oscillator. In practice, the differential pressure sensing means disclosed in this specification is the diaphragm of a microphone.However this type of detector suffers from two main disadvantages; firstly it is necessary for the microphone to make contact with the liquid, or at least be separated from it by a thin and hence fragile diaphragm; secondly microphones and other pressure sensors are particularly sensitive to fluid noise and pulsations resulting from, for example, pumps and external noise. Other methods of detection which have been tried are the differential cooling of an electrically heated wire, which requires a delicate wire to be mounted inside the flow meter; and movement of a metal ball in a small, secondary channel connecting for example, the two feedback channels. In this case, the position of a ball is detected by an electromagnetic proximity sensor.

This method is complex and susceptible to blockage and jamming of the ball.

According to this invention, a fluidic flow meter includes an ultrasonic transmitter arranged to transmit a sonic signal towards a portion of the fluid flow path through the fluidic oscillator in which oscillations occur, and a sonic receiver located for receiving the sonic signal after modulation by the oscillations.

The ultrasonic transmitter and receiver may be located across the main fluid inlet into the interaction chamber of the fluidic oscillator, across at least one of the feedback loops of the fluidic oscillator, across the fluid path on at least one side of the splitter, or preferably across the common outlet of the fluidic oscillator. Oscillations in the fluid flow past all of these locations are generated by the fluidic oscillator at a rate proportional to the velocity of fluid flow through the fluidic oscillator.

The generation of the oscillations results in a series of disturbances which affect the transmission of the sonic signal between the transmitter and the receiver. The effect that occurs may cause a greater quantity of the transmitted sonic energy to be reflected or refracted away from a direct path between the transmitter to the receiver so resulting in a reduction in the coupling between the transmitter and receiver when the transmitter and receiver are placed in direct opposition. Alternatively, the transmitter and receiver may be displaced from one another so that the receiver is arranged to pick up some of the sonic energy reflected or refracted from the disturbances in the fluid flow and, thus, in this case, the coupling between this transmitter and receiver is increased in the presence of the disturbance.It is also possible to measure the velocity of the flow of fluid using the Doppler shift that occurs between the transmitted and received signals at a particular point in the fluidic oscillator and so obtain a pulsed output signal, but this is not preferred.

Various examples of a fluidic flow meter in accordance with this invention will now be described with reference to the accompanying drawings, in which: Figure 1 is an isometric view of a first example; Figure 2 is a plan view of the first example; Figure 3 is a block diagram of a typical electronic circuit for use in this invention; Figure 4 illustrates a modification of the first example; Figure 5 is a combined plan view of second and third examples; Figure 6 is a plan view illustrating a fourth example; Figure 7 is a side elevation of the fourth example; Figure 8 is a combined plan view showing a modification of the first and fourth examples; Figure 9 is a side elevation of the modification of the first and fourth examples shown in Figure 8; and, Figure 10 is a plan view of a fifth example.

All of the examples are based on the same fluidic oscillator which will be described with reference to Figure 1.

Figure 1 shows the fluidic oscillator with its cover plate removed. The fluidic oscillator comprises an interaction chamber 1, a main fluid inlet nozzle 2, diverging side walls 3, and control nozzles 4. A splitter body 5 is located downstream from the interaction chamber 1 and divides the chamber into two separate channels. Feedback loops 6 interconnect the control nozzles 4 with the diverging side walls 3 downstream of the control nozzles 4. At junctions 7 between the feedback loops 6 and the side walls 3 the loops are inclined towards the portions of the side walls 3 extending between the control nozzles 4 and the junctions 7.

Restrictions 8 are provided downstream of the junction 7 and the two separate channels are combined downstream from the splitter body 5 to pass through a common outlet 9. In use, fluid is introduced into the fluidic oscillator through the main fluid inlet nozzle 2 and the fluid flow attaches itself to one or the other of the diverging side walls 3. The static pressure at the junction 7 increases when the flow is attached to its side wall 3 and this causes an increase in pressure in the associated feedback loop 6 and an increase in pressure at the associated control nozzle 4 so causing the fluid stream to detach itself from that side wall 3 and attach itself to the opposite wall 3.

This in turn leads to a change in static pressure in the other feedback loop 6 and, in turn, leads to the fluid flow being detached from the other side wall 3 and returned to the one side wall 3, and so on.

The repetition frequency of this cycle is dependent upon the velocity of fluid flow through the fluidic oscillator.

In the first example (Figures 1 and 2), an ultrasonic transmitting transducer 10 and an ultrasonic receiving transducer 11 are located on opposite sides of the fluidic oscillator downstream from the splitter 5 and immediately upstream from the common outlet 9. The transmitting 10 and receiving 11 transducers are isolated from the fluidic oscillator by isolating diaphragms 1 2 and in this example, the presence of disturbances in the fluid flow caused by the generation of oscillations in the fluidic oscillator reduces the coupling between the transmitting transducer 10 and receiving transducer 1 The output signal of the receiver 11 is modulated by the repetition frequency of the fluidic oscillator and hence dependent upon the velocity of flow through the fluidic oscillator.

A typical circuit for monitoring this modulation is shown in Figure 3. The circuit comprises a transmitter 13, the transmitting transducer 10, the receiving transducer 1 an amplifier 14, a detector 15, a pulse shaper 1 6 and a counter 1 7.

The transmitter 1 3 generates a sonic signal and applies it to the transmitting transducer 10. The sonic signal generated by the transmitting transducer 10 passes through the disturbances in the fluid flow and is modulated by the fluctuating flow field. The modulated sonic signal is received by the receiving transducer 11 and applied to the amplifier 14. The amplifier output signal is applied to the detector 1 5 which in essence is a demodulator that detects the modulation signal and generates pulses at the modulation frequency.

The pulses are shaped by the pulse shaper 1 6 and applied to the counter 1 7 whose count is proportional to the flow velocity.

In a first modification of this example, the splitter body 5 may be omitted as shown in Figure 4. When a splitter body is omitted the junctions 7 are positioned upstream from the equivalent position in Figure 1.

In a second modification of this first example, shown in Figures 8 and 9, the transmitting transducer 10' and receiving transducer 11' are located on a common axis which is set at right angles to that shown in Figure 1. However, the transmitting transducer 10' and receiving transducer 11' monitor the same portion of fluid path.

In the second example (Figure 5), an ultrasonic transmitting transducer 1 8 and a receiving transducer 1 9 are located on opposite sides of the main fluid inlet 2. Again, the transmitting and receiving transducers are isolated from the main fluid inlet 2 by a pair of isolating diaphragms 12.

Apart from the location of the transmitting and receiving transducers, this second example is substantially the same as the first.

In the third example (Figure 5), a transmitting transducer 20 and receiving transducer 21 are both located on the same side of the splitter body 5 to monitor flow in the channel on one side of the splitter body 5 downstream from the restriction 8.

The receiving transducer 21 is arranged to receive signals transmitted from the transmitting transducer 20 after reflection from the side of the splitter body 5. Again, disturbances in the fluid flow caused by the generation of oscillations in the fluidic oscillator lead to a change in the coupling between the transmitting transducer 20 and the receiving transducer 21 and so by monitoring the modulation of the received signal, it is again possible to determine the frequency of oscillation and hence determine the velocity of the flow through the fluidic oscillator. With the transducers 20 and 21 arranged in this way to provide a sonic path which is non-normal to the direction of fluid flow there is also some transient change in the frequency of the received sonic signal as a result of the Doppler effect. This may be used to provide some indication of the velocity of the fluid flow in the channel on the one side of the splitter body 5.

In the fourth example (Figures 6 and 7), an ultrasonic transmitting transducer 22 and a receiving transducer 23 are mounted above and below one of the feedback loops 6. The transducers 22 and 23 are both mounted on matching wedges 24 so that the sonic path between the transmitter and receiver once again involves a component in the direction of flow of the fluid. Thus, once again, in this example, not only is there an amplitude modulation in the coupling between the transmitting transducer 22 and the receiving transducer 23 caused by the presence of disturbances in the feedback loops 6, but there is also some transient change in the frequency of the received signal as a result of the Doppler effect.

In a modification of the fourth example shown in Figures 8 and 9, the transmitting transducer 22' and receiving transducer 23' are mounted directly above one another, so that the sonic path is normal to the direction of fluid flow.

In the fifth example (Figure 10), a transmitting transducer 25 and receiving transducer 26 are both mounted on matching wedges 27 so that any disturbances in the fluid flow in the chamber downstream from the splitter body 5 and upstream from the common outlet 9 increase the coupling between the transducers 25 and 26. In this case, a sonic signal transmitted by the transducer 25 is reflected or refracted from the disturbance so that it is received by the transducer 26 whereas, in the absence of a disturbance substantially no coupling occurs between the two transducers.

Claims

1. A fluidic flow meter comprising an ultraconic transmitter arranged to transmit a sonic signal towards a portion of the fluid flow path through the fluid oscillator in which oscillations occur, and a sonic receiver located for receiving the sonic signal after modulation by the oscillations.

2. A fluidic flow meter according to claim 1, further comprising means for monitoring the received sonic signal and providing an output related to the velocity of fluid flow through the fluid oscillator.

3. A fluidic flow meter according to claim 1 or claim 2, wherein the ultrasonic transmitter and receiver are located across a common outlet of the fluidic oscillator.

4. A fluidic flow meter according to any of the preceding claims, wherein the ultrasonic transmitter and the receiver are displaced relatively to one another in the general direction of fluid flow.

5. A fluidic flow meter according to claim 1, substantially as described with reference to any of the examples illustrated in the accompanying drawings.