GB2066463A - Improvements in or Relating to Fluid Flow Monitors - Google Patents

Abstract

A fluid flow monitor of the kind which detects the rate of formation of Karman vortices (8) caused by a vortex inducing element (7) in a fluid flow along a passage (1), in order to determine the velocity of flow of the fluid is provided with at least one formation (20) on the downside side of the element (7) extending into the passage to provide an obstruction to fluid flow along the passage. Ultrasonic sensing means (9, 11) are provided to detect the Karman vortices. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Fluid Flow Monitors The present invention concerns improvements in or relating to fluid flow monitors.

Fluid flow monitors detect movement of liquids or gases such as air and may use, for example, Pitot or Venturi tubes. Such monitors are often not entirely satisfactory because they require reading corrections to be made to allow for variations in the fluid away from calibration standard, for example, variations in atmospheric properties away from sea level.

Other types of monitor may employ a vane which is disturbed by relative movement of the fluid. Such monitors suffer from the disadvantage that in some environments, for example, an underground coal mine, they are susceptible to mechanical damage or the vane can become contaminated with dust.

Other types of fluid monitor rely on vortex shedding i.e. the vortices produced in a flowing fluid when an obstruction is placed in the fluid flow. The rate of vortex production tends to be proportional to the velocity of the fluid relative to the obstruction and for certain ranges this proportionality will be a near approximation to linear.

These types of fluid flow monitor can detect the vortices produced in a variety of ways. For example strain gauges can sense strain in members disposed in the fluid, which strain is caused by the vortices. Piezoelectric crystals, heated wires and thermistors, and diaphrams also can be used to detect the vortices.

Alternatively, a sonic signal is projected from a transmitter to a sonic receiver, the path of the sonic signal intersecting the vortex trail. Electrical circuitry converts the received sonic signal into an electrical signal and detects from this signal the frequency of the vortices which modulated the sonic signal.

In particular, although not exclusively, the present invention concerns improvements in or relating to fluid flow monitors of the kind described and claimed in our pending British patent application No. GB 2 020 022A which according to one aspect discloses a fluid flow monitor comprising transducer means which is disposable in a fluid flow, the transducer means being constructed to derive an electrical signal including modulations associated with vortices produced in the fluid flow, processing circuit means for processing the electrical signal and deriving a further electrical signal dependent upon the fluid flow, and comparator means for comparing said further electrical signal with a preselected reference signal, the comparator means having an output dependent upon the comparison with said preselected reference signals, which output is arranged to control said processing circuit means in response to the comparison.

British patent application No. GB 2 020 022A further discloses according to another aspect a fluid flow monitor of a type wherein a sonic transmitter transmits a sonic signal into the fluid flow and a sonic receiver receives the sonic signal, the sonic signal being modulated by vortices in the fluid flow, the monitor comprising transducer means associated with the sonic receiver for converting the received sonic signal to an electrical signal modulated at the frequency of passage of the vortices, demodulating means for demodulating the electrical signal, processing means for producing a further electrical signal from the demodulated signal, the further signal having magnitude dependent upon the modulation frequency of the electrical signal and comparator means for comparing said further electrical signal with a preselected reference signal, the comparator means being arranged to have an output dependent upon the comparison with said preselected reference signal, and the output of the comparator means being arranged to control said processing circuit means in response to the comparison.

With such a monitor the sonic transmitter and the sonic receiver are arranged on opposite sides of a passage for the fluid flow. Typically, at least a portion of the opposite sides of the fluid flow passage are inclined outwardly in the direction of fluid flow.

It has been found that such fluid flow monitors give accurate and reliable results over a limited range of fluid flow, for example, at relatively low fluid flow velocity but tend to give relatively inaccurate or unreliable results at fluid flow velocities falling outside said limited range of fluid flow.

An object of the present invention is to provide an improved fluid flow monitor which is able to increase the range of fluid flow velocities over which accurate and reliable results are obtained.

According to the present invention a fluid flow monitor comprises a head portion defining a passage for fluid flow to be monitored, a vortex inducing element arranged at least part way across the passage, sensing means for sensing the vortices induced by the element and for deriving a signal indicative of the sensed vortices, and at least one formation extending into the passage and tending to provide an obstruction to fluid flow along the passage, the formation being provided on the downstream side of the vortex inducing element.

Preferably, the formation tends to provide an obstruction to fluid flow in the vicinity of at least part of the sensing means.

Preferably, the passage defines a fluid flow inlet and a fluid flow outlet, the formation being adjacent to the fluid flow outlet.

Preferably, at least portions of the two opposed sides of the passage are relatively inclined outwardly in the direction of fluid flow along the passage.

Advantageously, two formations are provided, the formations being associated with the two opposed sides of the passage, respectively.

Conveniently, the sensing means comprises associated transmitter means and receiver means, the transmitter means and the receiver means being associated with the two opposed sides of the passage respectively.

Preferably, the transmitter means is a sonic transmitter arranged to transmit a sonic signal across the passage and the receiver means is a sonic receiver arranged to receive the sonic signal, the received sonic signal being modulated by the induced vortices in the fluid flow.

By way of example only, four embodiments of the present invention will be described with reference to the accompanying drawings, in which Figure 1 is a diagrammatic sectional view taken through a head portion of a fluid flow monitor constructed in accordance with a first embodiment of the present invention; Figure 2 shows calibration graphs A and B for two fluid flow monitors, graph B being the calibration graph for a fluid flow monitor constructed in accordance with the present invention; Figure 3 is a diagrammatic sectional view taken through a head portion of a fluid flow monitor constructed in accordance with a second embodiment of the present invention; Figure 4 is a diagrammatic sectional view taken through a head portion of a fluid flow monitor constructed in accordance with a third embodiment of the present invention; and Figure 5 is a diagrammatic cross-sectional view taken through a detail of a head portion of a fluid flow monitor constructed in accordance with a fourth embodiment of the present invention.

Like parts in each figure have been given the same reference numbers.

Referring to Figure 1 of the drawings which shows a diagrammatic sectional view substantially taken vertically along the longitudinal axis of a fluid flow passage 1 defined by a head portion 2 of a fluid flow monitor constructed in accordance with a first embodiment of the present invention. The passage has a fluid flow inlet 3 and a fluid flow outlet 4 and two opposed side walls 5 and 6 which are relatively inclined outwardly in the direction of fluid flow along the passage. The direction of fluid flow along the passage is indicated by arrowX.

In use, the monitor is situated in a fluid flow to be sensed such that the inlet 3 faces directly at the fluid flow. In one example the monitor is used to determine the velocity of mine air flowing along an underground roadway in a mine, the monitor being installed in the roadway such that the inlet faces directly along the roadway in order that the mine air can flow straight through the monitor.

The monitor also comprises a vortex inducing element 7 arranged at least part way across the passage in the vicinity of the inlet 3. As fluid, e.g.

mine air, flows around the element 7 a trail of Karman vortices 8 is induced along the passage downstream of the element, the induced vortex trail pattern being indicative of the fluid velocity flowing along the passage. The vortex trail 8 is sensed by sensing means comprising a sonic transmitter 9 in one wall 5 arranged to direct a sonic signal 10 across the passage and the Karman vortex trail 8 to sonic receiver 11 associated with the passage side wall 6.

The amplitude of the sonic-signal is modulated by its interference with the vortex trail.

The sonic receiver 11 includes electrical transducer means 12 which derives an electrical signal indicative of the received sonic signal, the derived electrical signal being fed along line 1 3 to monitor means 14 including comparator means 1 5 adapted to compare the derived signal with a preselected signal enabling the monitor means to derive an electrical difference signal indicative of the velocity of fluid flowing along the passage.

The electrical difference signal is fed to a record and/or display instrument which either records the sensed velocity and/or displays the velocity on, for example, a graduated meter. The record and/or display means may be part of the monitor means 14. Alternatively, the record and/or display means is remote from the monitor means.

The sonic transmitter 9 is fed with a suitable power supply from a power unit 16 via line 17. A similar power supply line (not shown) is fed to the sonic receiver 11.

The monitor also includes two formations 20 and 21 associated with the passage side walls 5 and 6, respectively, and each constituted by a projection extending into the passage thereby tending to provide an obstruction to fluid flow along the passage in the vicinity of the means 9, 11 for sensing the vortex trail 8. The formations 20, 21 are provided on the downstream side of the vortex inducing element and of the sensing means 9, 11. In the embodiment illustrated in Figure 1 the formations 20 and 21 are located adjacent to the fluid flow outlet 4 and define an outlet substantially having the same area of cross section as the fluid flow inlet.

Referring now to Figure 2, this shows two calibration graphs A and B, associated with two different fluid flow monitors in which the vertical ordinate plots frequency in Hertz against the fluid flow velocity in metres per second and the horizontal ordinate. The monitor associated with graph A was somewhat similar to that illustrated in Figure 1 but did not include the formations 20, 21 at the end of the passage 1. From Figure 2 it can be seen that at relatively low fluid flow velocities, i.e. within a range 0.5 to 7 metres per second, the monitor had a substantially linear calibration graph. However, at increased fluid flow velocities, i.e. over 7 metres per second, the calibration graph is not linear and at velocities above 9 metres per second the graph exhibits a downward trend. Thus, for a derived electrical signal of around 500 Hertz two possible readings of fluid flow are possible. Consequently, such a fluid flow monitor is unsuitable for sensing fluid flows over 7 metres per second. Such a limitation greatly reduces the operational scope of the monitor.

Graph B of Figure 2 shows the calibration graph associated with a fluid monitor constructed as illustrated in Figure 1 and including the two formations 20 and 21. As seen in Figure 2 Graph B is linear throughout the desired operational range of fluid flow, i.e. from 0.5 metres per second to up to 10 metres per second. Thus, it will be appreciated that a fluid flow monitor constructe in accordance with the present invention increases the operational range of fluid flow velocities thereby providing a greatly improved monitor.

In addition, in practice the fluid flow monitor constructed in accordance with the present invention tends to be less troublesome to set up than the prior known monitors of the vertex shedding type, the selected operational frequency of the sonic signal is less critical thereby greatly reducing the initial setting up procedure.

Typically, the operational frequency of the sonic signal lies in a range 140 to 160 KHz.

Figure 3 illustrates a second embodiment of fluid flow monitor constructed in accordance with the present invention.

The monitor shown in Figure 3 to which reference is now made differs from the first described embodiment because the formations 20 and 21 which abutted to side walls 5 and 6, respectively, have been replaced by formations 30 and 31 which are constituted by projections suitably supported and spaced from the associated side walls to define tortuous paths which tend to provide obstructions to fluid flow along the passage in the vicinity of the sensing means 9, 11 but which provide escape channels 34 and 35 for any dust particles which otherwise may have tended to gather in the pockets defined by the formations.Consequently, dust settling on the side walls will tend to be swept by the fluid flow through the escape channels 34 and 35 existing between the formations 30 and 31 and the associated side walls, thereby tending to increase the operational life of the monitor in dusty conditions such as may be expected in a coal mine. The formations 30 and 31 also include guide elements 32 and 33 respectively, provided adjacent to the outlets of the associated escape channel.

In another embodiment (not shown) only the formation associated with the lower side wall of the passage is spaced from the side wall.

The passage 1 in Figure 3 is shown to comprise a parallel sided section 51,61 adjacent to the passage inlet 3 and an outwardly inclined section 52, 62 adjacent to the passage outlet 4.

Figure 4 illustrates a third embodiment of the present invention. The formations 40 and 41 are.

constituted by projections arranged to abut the associated side walls 5 and 6 respectively.

However, the inward facing surfaces 42 and 43 of the formations are curved thereby tending to ensure that any dust particles tending to settle on the side walls 5 and 6 are swept by the fluid flow and carried towards the outlet 4 thus increasing the operational life of the monitor in dusty conditions.

This embodiment of the present invention may be modified by providing only one of the formations with an inward facing curved surface or in providing only one curved formation.

In a further modification more than two formations can be provided.

Figure 5 shows a part of a formation 50 of a fourth embodiment of the present invention, the formation 50 being viewed in a direction along the fluid flow passage. As seen in the drawing, the formation comprises a screen 53 which tends to provide an obstruction to fluid flow along the passage in the vicinity of the means for sensing the vortex trail. However, the screen is provided with a number of apertures 54 tending to provide escape means for dust particles which otherwise might be trapped by the formation 50.

In further embodiments of the invention only portions of the passage side walls are relatively inclined outwardly in the direction of the fluid flow, for example the opposed passage side walls may be parallel upstream of the sensing means 9, 11 for sensing the vortex trail 8. Alternatively, portions of the opposed side walls may be inclined outwardly in a direction opposite to the direction of fluid flow, for example the portion of the opposed side walls upstream of the sensing means 9, 11 for sensing the vortex trail 8.

In other embodiments of the invention opposed side walls of the passage are parallel.

The passage may also be tubular.

In still other embodiments of the invention the formation tending to provide an obstruction of fluid flow is integral with the monitor head defining the passage.

In the embodiments therefore described and illustrated, the formations are disclosed as being downstream of the sensing means. The invention will also opperate effectively if the formations are located between the element and the sensing means.

Claims (1)

1. Claims

   1. A fluid flow monitor comprising a head portion defining a passage for fluid flow to be monitored, a vortex inducing element arranged at least part way across the passage, sensing means for sensing the vortices induced by the element and for deriving a signal indicative of the sensed vortices, and at least one formation extending into the passage and tending to provide an obstruction to fluid flow along the passage, the formation being provided on the downstream side of the vortex inducing element.

   2. A monitor as claimed in claim 1, in which the formation tends to provide an obstruction to fluid flow in the vicinity of at least part of the sensing means.

   3. A monitor as claimed in claim 1 or 2 in which the passage defines a fluid flow inlet and a fluid flow outlet, the formation being adjacent to the fluid flow outlet.

   4. A monitor as claimed in claims 1,2 or 3, in which at least portions of two opposed sides of the passage are relatively inclined outwardly in the direction of fluid flow along the passage.

   5. A monitor as claimed in claim 4, in which two formations are provided, the formations being associated with the two opposed sides of the passage, respectively.

   6. A monitor as claimed in any one of the preceding claims, in which the sensing means comprises associated transmitter means and receiver means, the transmitter means and the receiver means being associated with the two opposed sides of the passage, respectively.

   7. A monitor as claimed in claim 6, in which the transmitter means is a sonic transmitter arranged to transmit a sonic signal across the passage and the receiver means is a sonic receiver arranged to receive the sonic signal, the received sonic signal being modulated by the induced vortices in the fluid flow.

   8. A monitor as claimed in any one of the preceding claims in which the or at least one of the formations comprises a projection extending into the passage.

   9. A monitor as claimed in claim 8, when dependent upon claim 3 in which the projection abuts the associated passage side.

   10. A monitor as claimed in claim 8 when dependent upon claim 3, in which the at least part of the projection is spaced from the associated passage side.

   11. A monitor as claimed in claim 8, 9 or 10 in which the at least one formation defines, or in which the at least one formation is arranged to provide, escape means for dust particles.

   12. A monitor as claimed in claim 7, 8, 9, 10 and 11 or in which the projection has a curved inward facing surface.

   1 3. A fluid flow monitor substantially as described herein and substantially as shown in Figure 1, Figure 3, or Figure 4, or Figure 5 of the accompanying drawings.

   New Claims or Amendments to Claims filed on 6/6/80 Superseded Claim 1.

   New or Amended Claims:

   1. A fluid flow monitor comprising a head portion defining a passage for fluid flow to be monitored, a vortex inducing element arranged at least part way across the passage, sensing means for sensing the vortices induced by the element and for deriving a signal indicative of the sensed vortices, and at least one formation associated with a side wall of the passage and extending into the passage and tending to provide an obstruction to fluid flow along the passage, the formation being provided on the downstream side of the vortex inducing element.