GB2049925A - Flow rate sensor - Google Patents

Abstract

A sensor of the rate of flow of a fluid through casing (111) in direction (113) has a freely rotating rotor (115), on which the fluid impinges. The inside surface of the hub of the rotor (115) is formed by alternate reflective (144) and non-reflective (146) surfaces. Light from a source (120) impinges on these surfaces and is either reflected back to a light detector (119) or not depending on which of the surfaces (144, 146) the light falls on. Pulses produced by the detector corresponding to the interruption of light to it, are used to indicate the rate of flow. The sensor is combined with rotor (112) which drives the fluid (ambient air) through casing (111). Alternatively the freely rotating rotor may chop the light sent from source to detector; or it may be combined with a centrifugal blower and the freely rotating rotor may be in a recess. <IMAGE>

Description

SPECIFICATION Flow rate sensor This invention relates to a fluid flow rate sensor capable of giving a usable signal representative of the quantity of air or other gas, or liquid flowing along a fluid flow passage. One example of a use of the invention is to be able to measure the rate of flow of air being pumped to breathing apparatus so that a warning can be given if the flow rate falls below what is necessary for the breather's safety.

According to the present invention, a flow rate sensor comprises a rotor having one or more blades arranged to be driven by fluid flowing in a flow passage, the rotor aiso having a light interrupter arranged to interrupt repeatedly the passage of light from a light source to a light detector as the rotor rotates.

in a preferred form the light interrupter may comprise at least one non-reflective surface so that the light from the source is either reflected onto the detector or not depending on the position of the rotor. These non-reflective surfaces may be positioned on the hub of the rotor.

In a preferred form, the rotor comprises an integral moulding or assembly of a turbine wheel with a number of generally radially extending blades, and an interrupter comprising a rotary blade which moves into and out of the path of light from the source to the detector as the rotor rotates.

The rotor blades may be mounted to rotate in a chamber formed as part of or assembled with a housing for a blower.

The blower housing can be fitted into or connected to a helmet or other respirator for example, for use by an industrial worker, working in a contaminated atmosphere. Then air can be drawn in through a filter and pumped to the region of the user's nose and mouth and the light detector can give a signal representative of the rate of flow.

The source and detector could, for example, be constituted by a light emitting diode and a photosensitive detector, the output of which will be in pulses corresponding with interruption of the light beam: those pulses can be counted electronically over predetermined periods to give a visual or aural or other warning that the air flow has dropped below a safe level and the user can no longer safely breathe through the respirator apparatus, but should leave the contaminated area and take the apparatus off.

The invention may be carried into practice in various ways, and two embodiments will be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a side elevation with parts cut away of an air blower and a first embodiment of the flow rate sensor; Figures 2, 3 and 4 are respectively sections on the lines A-A, B-B, and C-C in Figure 1: Figure 5 is a cross-section of an air blower and the second embodiment of the flow rate sensor; Figures 6 and 7 are respective sections on the lines A-A and B-B in Figure 5; Figure 8 is a section on the line C-C in Figure 7: and Figure 9 is a view in the direction of arrow D in Figure 5.

Referring first to Figures 1 to 4, a blower comprises a casing 11 having a conventional centrifugal rotor 12 for drawing in ambient air axially, and impelling it tangentially as indicated by the arrow 13 through an outlet passage 14 connected to the region in a respirator helmet leading to the nose and mouth of the wearer.

There is a filter (not shown) upstream of the rotor 1 2 for filtering from the air stream particles that would be dangerous if breathed in by the user. The blower may be fitted into a respirator helmet, or may be external of it connected to it through a flexible pipe. The rotor 1 2 is conveniently battery driven.

In order to provide a measure of the rate of air flow through the passage 14, a rotor 1 5 having eight external radial blades 1 6 is mounted in a rotor chamber formed in a wall of the casing 11, with the blades just projecting into the air flow passage as the rotor 1 5 is rotated by the flow of air.

The rotor 1 5 is a plastics moulding, and integral with it is a two-bladed shutter 1 7 mounted to rotate on the same axis 18, with the shutter blades arranged to interrupt repeatedly the passage of light from a light emitting diode 20 to a photo-sensitive detector 19. The photo-sensitive detector 1 9 will produce an output signal consisting of pulses corresponding to the periods between interruption of the light beam, and the pulse frequency will be a measure of the rate of rotation of the rotor 1 5, and thus of the rate of flow of air from the blower 12 through the passage 14.

The output from the detector 1 9 is fed to a conventional electronic counter arranged to count over repeated periods of constant duration, so that the respective counts will be a measure of the rate of rotation. If the signal corresponds to a rate of flow less than a precalculated minimum rate for supplying the user's breathing requirements, it can be arranged to give a visual or aural warning, so that the user can get out of the contaminated area in which he is working and take off the helmet to breathe fresh air.

Figures 2 and 3 show how the passage 14 and the chambers for the rotor 1 5 and shutter 17 are defined between two components being indicated in section in Figures 2 and 3, at 22 and 23. Each is formed with a hole constituting a bearing for the rotor shaft 18, and the rotor shaft can be simply fitted between them as the components 22 and 23 are fitted together. There may be P.T.F.E. or other long-life bearings (not shown) for the shaft to run in. The component 23 is also formed with passage 25 for the electrical leads to the electrooptical components 1 9 and 20.

Referring now to the second embodiment shown in Figures 5 to 9, a blower comprises a casing 111 including a rotor 112 for drawing in ambient air and impelling it, as indicated by arrows 1 3, through an outlet passage 114. The blower of the second embodiment may be situated in the same location in a respirator helmet as that described above in relation to the first embodiment.

The rotor 112 is driven by a motor 140 which is positioned in the casing 111, and may conveniently be powered by a battery.

In order to provide a measure of the rate of air flow through the casing 111, a rotor 11 5 is mounted in the outlet passage 114, the rotor 11 5 being free to rotate about a spindle 142 so that a flow of air in the direction of arrows 113 caused by rotation of rotor 11 2 impinges on the blades of rotor 11 5 and causes rotor 11 5 to rotate.

The rotor 11 5 may be a plastics moulding and, as seen in Figure 6, is formed with alternate reflective and non-reflective surfaces 144 and 146 respectively over a portion of its surface facing the motor 140.

A photo-sensitive detector 11 9 and a light emitting diode 120 are mounted in the end of the motor housing, as shown in Figure 7, and face the surfaces 144 and 146 so that when light from the diode 120 falls on the reflective surface 144, it is reflected back and received by the detector 11 9, as shown in Figure 8. Alternatively, when light from the diode 1 20 falls on the non-reflective surface 146, the light is not reflected and the detector does not register as having seen any light.Thus, as the rotor 11 5 is turning about its axis, the photo-sensitive detector 11 9 produces an output signal consisting of pulses corresponding to the periods between the interruption of the reflected light beam, and the pulse frequency will be a measure of the rate of rotation of the rotor 11 5 and thus of the rate of the flow of air produced by the rotor 11 2 through the housing 111.

The output from the detector 11 9 may be used in the same way as the output from the detector 1 9 described in relation to the first embodiment above.

Figure 9 shows the rotor 1 72 having nine blades, although it may be preferable to provide more or less numbers of blades, for example five blades.

It will be appreciated that in the first embodiment the surface of the rotary member could be reflective to give a path of light to the now repositioned detector 1 9 once or twice every revolution or that, in the second embodiment, the detector 11 9 and diode 120 could be positioned on opposite sides of the rotor 11 2 and the reflective surfaces 144 could be cut away.

The sensor is simple to make, and is compact and light and yet can give an accurate continuous measure of the rate of air flow. The electrical circuits can be powered by a small battery, or could indeed use the same battery that drives the impeiler 12 or 112.

Claims (14)

1. A flow rate sensor comprising a rotor having one or more blades arranged to be driven by fluid flowing in a flow passage, the rotor also having a light interrupter to interrupt repeatedly the passage of light from a light source to a light detector as the rotor rotates.

2. A sensor as claimed in Claim 1 in which the light interrupter comprises at least one nonreflective part of a surface lying in the path of the light from the source to the detector.

3. A sensor as claimed in Claim 1 or Claim 2 in which the light interrupter is on a part of the rotor which is adjacent to the axis of rotation of the rotor.

4. A sensor as claimed in any preceding claim in which the rotor is concentrically located within a circular flow passage.

5. A sensor as claimed in Claim 1 in which the light interrupter is positioned between the light source and the light detector.

6. A sensor as claimed in Claim 5 in which the interrupter comprises at least one rotary member which moves into and out of the path of light from the source to the detector as the rotor rotates.

7. A sensor as claimed in any preceding claim in which the rotor includes a number of generally radially extending blades.

8. A sensor as claimed in Claim 7 in which the light interrupter is displaced from the blades along the axis of rotation of the rotor.

9. A sensor as claimed in Claim 6 or Claim 7 when dependent on Claim 6, in which, in use, the rotary member defines a path which is perpendicular to the axis of rotation of the rotor.

1 0. A sensor as claimed in any preceding claim in which the rotor is mounted in a recess so that only a portion of the area of the blades projects into the flow at any one time.

11. A sensor as claimed in any preceding claim in which a visual, oral or other warning is given when the air flow has dropped below a predetermined value.

12. A sensor as claimed in any preceding claim in which the detector produces an output of pulses corresponding to the interruption of the light beam.

13. A sensor as claimed in Claim 12 in which the pulses are counted electronically over predetermined periods to give a visual, oral or other warning that the air flow has dropped below a predetermined level.

14. A sensor as claimed in any preceding claim in which the flow is caused by an axial blower.

1 5. A sensor as claimed in any of Claims 1 to 1 3 in which the flow is caused by a centrifugal blower.

1 6. A flow rate sensor substantially as herein specifically described with reference to Figures 1 to 4 or 5 to 9 of the accompanying drawings.

1 7. A respirator helmet incorporating a flow rate sensor as claimed in any preceding claim.