EP0400044A1 - Device and method capable of detecting small particles in a fluid - Google Patents

Device and method capable of detecting small particles in a fluid

Info

Publication number
EP0400044A1
EP0400044A1 EP19890902396 EP89902396A EP0400044A1 EP 0400044 A1 EP0400044 A1 EP 0400044A1 EP 19890902396 EP19890902396 EP 19890902396 EP 89902396 A EP89902396 A EP 89902396A EP 0400044 A1 EP0400044 A1 EP 0400044A1
Authority
EP
European Patent Office
Prior art keywords
light
passageway
fluid
detecting
particle
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP19890902396
Other languages
German (de)
French (fr)
Inventor
Philip John Lloyd
Ian Sinclair
Nigel Maddocks
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Loughborough Consultants Ltd
Original Assignee
Loughborough Consultants Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GB888802330A external-priority patent/GB8802330D0/en
Application filed by Loughborough Consultants Ltd filed Critical Loughborough Consultants Ltd
Publication of EP0400044A1 publication Critical patent/EP0400044A1/en
Pending legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N21/49—Scattering, i.e. diffuse reflection within a body or fluid
    • G01N21/53—Scattering, i.e. diffuse reflection within a body or fluid within a flowing fluid, e.g. smoke
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/47—Scattering, i.e. diffuse reflection
    • G01N2021/4704—Angular selective
    • G01N2021/4707—Forward scatter; Low angle scatter

Definitions

  • This invention relates to a device and a method capable of detecting individual particles of less than 10 microns in diameter in a fluid.
  • a small quantity of fluid is sampled and passed through a small cross- section passageway. All the particles in the sample are counted by illuminating the sample with a uniform beam of light and detecting light scattered by "each of the particles as they pass through the beam.
  • the passageway In order to detect and count the individual flashes of scattered light as each of the particles passes through the beam of light, the passageway must have a very small cross- sectional area (for example 1 to 5 mm 2 ) and a very low flow rate of fluid must be used (for example 0.1 litres per minute) , thereby ensuring that only a few particles pass through the beam per unit time.
  • the device cannot, usually, be installed directly in line in a fluid-distribution system carrying a much greater fluid flow-rate of, for example, 15 litres per minute. It must therefore be fitted in a specially constructed branch line and does not then monitor continuously the fluid flowing along the main line. Further, the devices presently available are prohibitively expensive so that, if used at all, only one such device can normally be afforded. When monitoring a large fluid-distribution system it is normally necessary therefore to transfer the device between, several different sampling points so that continuous monitoring at each point is not possible and even a dramatic increase in particle concentration, for example as a result of failure of a filter, may go undetected.
  • a device capable of detecting individual particles of less than 10 microns diameter in a fluid flowing through the device, the device including a body having a passageway through which, in use, the fluid flows, a light source for directing a beam of light into the passageway and a light detector for detecting 5 scattered light from a small portion only of the cross- sectional area of the passageway, the arrangement being such that light from the light source is unable to pass directly to the light detector.
  • the device may therefore be interposed 5 in a pipeline in a fluid-distribution system to monitor the fluid flowing through the pipeline continuously without impeding the flow.
  • By detecting light scattered by particles it is able to sense particles of sub-micron size, and because individual particles are detected, it 0 is possible to measure very low concentrations of particles.
  • the device is therefore able to detect very low concentrations of very small particles in fluids flowing through the device at a high rate, and may be used for particle-detection in either liquids or gases, 5 for example deionized water, sea water (for example in the offshore oil industry), aviation fuel, hydrogen fluoride and environmental air.
  • liquids or gases 5 for example deionized water, sea water (for example in the offshore oil industry), aviation fuel, hydrogen fluoride and environmental air.
  • the small portion of the cross-sectional area of the passageway from which light is detected may comprise less than 5% of the total cross-sectional area of the passageway.
  • the passageway may have a cross-sectional area of at least 100mm 2 enabling high flow rates of liquid to be accommodated.
  • the light detector may be arranged to detect for ⁇ ward-scattered light, with its optical axis subtending an angle of less than 90°, and advantageously less than 30 and preferably approximately 25° with the axis of the incident beam of light. Detecting forward-scattered light improves the ability of the device to detect very small particles which scatter only a small amount of light.
  • the light source may be arranged to direct a parallel beam of light into the passageway, and the diameter of the beam is preferably less than 2mm.
  • the light source may be arranged to bring the beam of light to a focus at a region within the passageway.
  • the light detector includes a light sensor and means for focusing light emanating from the small portion of the passageway onto the sensor. The scattered light will thereby be concentrated on the sensor, greatly increasing the sensitivity of the device.
  • the arrangement is preferably such that light scattered from the focal point of the beam is focused onto the light sensor.
  • the light source may include a laser, and the body may be provided with a first fluid-tight window through which, in use, the beam of light enters the passageway, and a second fluid-tight window through which the light detector receive the scattered light.
  • the output of the light detector may be connected to a signal-monitoring device which may be arranged to provide the same output in response to receipt of a signal from the light detector, regardless of the level of the signal, provided the level is above a predetermined threshold value. This enables the signal monitoring device to produce an output indicative of the number but not the size of the particles in the passageway.
  • the signal-monitoring device may be connected to a counter and/or to an alarm system for providing a warning of the presence of an excessive number of particles, and/or to a printer for providing a permanent record of the output of the monitoring device.
  • the signal-monitoring device may further be connected to a computer for processing the output of the signal-monitoring device.
  • the present invention further provides a device for detecting particles in a fluid, the device including a body having a passageway through which, in use, the fluid flows, a light source for directing an incident beam of light into the passageway and a light detector for detecting light scattered from a small portion of the passageway, the light detector including a light sensor and a lens for focusing light emanating from the small portion of the passageway onto the sensor, the optical axis of the light detector being angularly displaced from the axis of the incident beam by an amount sufficient to prevent the incident beam from falling directly upon the sensor.
  • the present invention yet further provides a fluid-distribution system including a particle-detecting device as described above and a pipeline for distributing a fluid, the particle-detecting device being interposed in the pipeline so that, in use, all the fluid distributed by the pipeline passes through the device.
  • the system may include a plurality of particle- detecting devices, all of which are connected to a computer for monitoring the number of particles at a plurality of different points around the system.
  • the fluid-distribution system may be a deionised water distributing system.
  • a method capable of detecting individual particles of less than 10 microns in diameter in a fluid in which the fluid is caused to flow through a passage ⁇ way, a beam of light is directed into the fluid in the passageway and light scattered from a small portion of the cross-sectional area of the passageway is detected without detecting the incident beam of light directly.
  • the small portion of the passageway may comprise less than 5% of the cross-sectional area of the passageway.
  • the passageway may have a cross-sectional area of at least 100mm 2 .
  • the flow-rate of fluid through the passageway may be at least 1 litre per minute.
  • Forward-scattered light may be detected, with the optical axis of the detected light subtending an angle of less than 90 , and advantageously less than 30°, and preferably approximately 25°, with the axis of the incident beam of light.
  • Figure 1 shows, in perspective, a device for detecting particles in a fluid
  • Figure 2 is a cross-section along line II-II of Figure 1 .
  • Figures 3a and 3b show, diagrammatically, an optical arrangement incorporated in the device shown in Figure 1.
  • the particle- detecting device includes a body member 1 through which there extends a cylindrical passageway 2 having a diameter of 25mm. Extending through the cylindrical wall of the body member 1 are two cylindrical bores 3 and 4. The axes of the bores 3 and 4 are perpendicular to the longitudinal axis of the passageway 2 and they intersect one another at a point midway along the length of the passageway 2 and on the longitudinal axis thereof, where they subtend an angle of 155 . The axes of the bores 3 and 4 are coincident with the line II-II.
  • the body member 1, for example, is constructed in one piece of PVDF.
  • each bore 3 and 4 there is provided a portion of slightly reduced diameter which forms an inwardly-extending lip 7.
  • a quartz window 8 Positioned towards the inner end of each bore 3 and 4 to abut the lip 7 is a quartz window 8.
  • the window 8 is urged towards the lip 7 by a hollow clamping screw 9 which engages a screw thread 10 provided at the outer end of each bore 3 and 4.
  • An O-ring 11 is located between the window 8 and the clamping screw 9, and the face of the clamping screw which contacts the O-ring is provided with a bevelled surface 12 which, when the clamping screw is tightened, forces the O-ring outwardly against the inner surface of the respective bore 3 or 4, thereby forming a fluid-tight seal between the window and the bore.
  • the device is capable of withstanding a fluid pressure substantially above ambient pressure and a temperature substantially above a typical ambient temperature (20 C) .
  • the device is capable of operating at a fluid pressure of 70psi (5Xl0 5 N/m 2 ) and a temperature of 70°C.
  • a light source 13 for example a laser, is attached to the body member 1 at the mouth of the bore 3 and is arranged to direct a narrow, parallel beam of light along the axis of the bore 3 and through the window 8 into the passageway 2 in the body member 1.
  • the light source 13 is provided with an external screw thread 1 which engages the screw thread 10 towards the outer end of the bore 3.
  • a light detector 15 is attached in a similar manner at the mouth of the second bore 4, to detect light passing through the window 8 into the bore.
  • the narrow beam of light from the light source 13 passes through the first window 8 into the passageway 2.
  • the beam passes approxi ⁇ mately through the centre of the passageway 2 and is absorbed by the opposite wall.
  • the beam has a diameter D of approximately 1mm and therefore illuminates only a relatively small fraction of the cross-sectional area of the passageway, and none of the incident light passes directly to the light detector 15, due to the offset angle of 25 .
  • the light detector 15 includes a converging lens 21, and a photocell 22.
  • the lens 21 and the photocell 22 are so arranged that only light emanating from a small portion A of the cross-section of the passageway 2 and passing through the window 8 in the second bore 4 is focused onto the photocell and detected.
  • the lens 21 and the window 8 have a relatively large diameter in order to collect a substantial proportion of the light scattered from the small portion A, but without collecting any of the incident beam of light.
  • the small portion A of the cross-sectional area of the passageway which is monitored by the light director 15 coincides with the path of the incident beam of light, and only those particles which pass through the beam in the small portion A are sensed. Since the number of particles which pass through the small portion A per unit time is related to the total concentration of particles in the fluid flowing through the passageway 2, the concentration can be calculated.
  • the approximate area of the small portion A which is monitored by the light detector 15 is shaded in Fig. 3b and, as can be seen in that figure, its size is determined by the diameter D of the incident beam of light and the field of view F of the detector 15. Only particles which pass through the portion A - i.e. those particles which are illuminated by the beam of light whilst within the field of view of the detector 15 - are detected.
  • the small portion A has a cross-sectional area of approximately 2.4mm 2 , and the passageway has an area of 500mm 2 .
  • the small portion A therefore comprises less than ⁇ % of the total cross-sectional area of the passageway in this example.
  • the area occupied by the portion A may in other examples be higher (for example up to 1% or even 5%).
  • the photocell 22 is provided with an output terminal 23 which is connected to a device (not shown) for monitoring the signals derived from the photocell.
  • the cylindrical body member 1 is connected in-line with a pipe of a fluid-distribution system, so that the fluid distributed by the system flows through the passageway 2 with a high flow rate of, for example between 5 and 50 litres/minute.
  • the fluid passing through the passageway 2 carries any particulate matter, light will be scattered from the incident beam whenever a particle passes through it.
  • the light detector 15 is sensitive only to light scattered from the small portion A of the passageway, only those particles which pass through the beam in the small portion A will be detected. Because light is scattered from a particle mostly in a forward direction, and since the window 8 and the lens 21 have a large aperture, the amount of light reaching the photocell 22 will be relatively large, and will depend on, amongst other factors, the size of the particle and the intensity of the incident beam of light.
  • a voltage pulse is generated which is monitored at the output 23 by the signal-monitoring device (not shown) .
  • the monitoring device senses the voltage pulse and, provided that the amplitude of the pulse exceeds a predetermined discrimin- ation level, produces an output pulse independent of the height of the sensed pulse.
  • the monitoring device therefore produces a series of identical output pulses, the frequency of which is indicative of the concentration of particles in the fluid having a diameter greater than a predetermined minimum value.
  • the device does not however indicate the actual sizes of the particles.
  • the monitoring device is connected to an alarm system which provides a warning whenever the particle concentration exceeds a predetermined level, that is whenever the number of received signals per unit time exceeds a predetermined level.
  • the alarm could also be arranged to be triggered by either of the following conditions: (i) a short-term surge of particles of above a certain level is detected, or (ii) the detection rate exceeds the ability of the device to distinguish separate particles.
  • the monitoring device may also be connected to a counter which may have a digital or analogue display, and/or to a printer for providing a permanent record of the particle concentration in the fluid over an extended period of time.
  • the monitoring device may also provide a computer-readable output.
  • the fluid-distribution system may include several particle-detecting devices positioned at different points around the system for providing a comprehensive particle detection system, and the outputs of the various devices may be connected to a computer for monitoring the particle-concentration at different parts of the fluid- distribution system simultaneously.
  • the particle-detecting devices may be activated manually, or by a clock, or by flow-sensing devices which activate the particle-detecting devices only when fluid is flowing through them.
  • the devices may be activated by a central computer.
  • the cylindrical body 1 may be manufactured from other machinable or mouldable materials, for example polyvinylchloride (PVC), nylon or stainless steel, and the window 8 may be of other transparent materials, for example glass, or, particularly for use with corrosive liquids, sapphire.
  • the O-rings 11 may be manufactured from silicone rubber or fluorine-based rubber, such as that sold under the trade mark "Viton" , or other suitable material.
  • the light source 13 is arranged to bring the incident beam of light to a focus at the centre of the passageway 2, and the light detector 15 is arranged to detect only light scattered from the focal point of the incident beam.
  • the size of the small portion of the passageway from which scattered light is detected may be reduced, and the intensity of light in that portion increased, thereby allowing even smaller particles to be detected whilst still using a large passageway to permit a high fluid flow-rate.
  • the light source for the particle-detecting device may include a laser as described or a filament bulb, and the light source may provide visible, infra-red or ultra-violet light.
  • the light source may be located adjacent to the bore 3 or at a remote location, with the light transmitted into the bore by reflection, refraction or by an optical fibre.
  • the light detector may similarly be remotely located and connected to the device by an optical fibre.
  • a light-absorbing device such as a Rayleigh horn, may be provided to absorb the incident beam after it has crossed the passageway.
  • the dimensions of the device may vary consider ⁇ ably from those given in the embodiment described above and in particular, if the device is used for detecting particles in a gas a passageway with a much smaller cross-sectional area may be used. In any case, however, the area of the small portion monitored by the light detector will be very small, for example 10% or less of the cross-section of the passageway.
  • the photocell 22 in the light detector may be a photo-diode, and may incorporate an operational amplifier to increase the size of the signal delivered to the monitoring device.
  • the light-detector may be provided with mu-metal shielding.
  • the device is capable of accommodating a high flow-rate of fluid through the passageway 2
  • fluids having extremely high flow-rates such as, for example, aviation fuel being pumped into an aircraft's fuel tanks
  • the device may be mounted in a by-pass pipe so as to receive only a proportion of the flow of fluid through the main pipeline.
  • the flow rate through the by-pass can still be relatively high, for example 15 litres per minute.
  • the particulate contaminants found in aviation fuel typically have a diameter of between 0.8 and 10 microns.

Abstract

Dispositif permettant de détecter des particules isolées de moins de 10 microns de diamètre dans un fluide traversant le dispositif. Il comporte un corps (1) pourvu d'un conduit (2) par lequel, si lorsqu'on utilise ce dispositif, le fluide s'écoule, ensuite une source lumineuse (13) pour pouvoir diriger un faisceau de lumière dans le conduit (2), enfin un détecteur de lumière (15) permettant de détecter la lumière dispersée et provenant d'une faible partie seulement de la superficie de la section du conduit (2). La disposition est telle que la lumière émise par la source lumineuse (13) ne peut frapper directement le détecteur de lumière (15). Ce dispositif permet de détecter de très faibles concentrations de particules dans les fluides qui le traversent à grand débit.Device for detecting isolated particles less than 10 microns in diameter in a fluid passing through the device. It comprises a body (1) provided with a conduit (2) through which, if this device is used, the fluid flows, then a light source (13) in order to be able to direct a beam of light in the conduit ( 2), finally a light detector (15) making it possible to detect scattered light coming from only a small part of the area of the section of the duct (2). The arrangement is such that the light emitted by the light source (13) cannot directly strike the light detector (15). This device makes it possible to detect very low concentrations of particles in the fluids which pass through it at high speed.

Description

Device and method capable of detecting small particles in a fluid
This invention relates to a device and a method capable of detecting individual particles of less than 10 microns in diameter in a fluid.
There is a need for a device which can detect particles having a diameter of less than 10 microns in a fluid flowing through the device in industries requiring very clean fluid supplies. For example particles having a diameter in the range of 0.3 to 1 micron in the deionized water circuits required in the semi-conductor industry can damage the components being manufactured and, although filters can remove most of the particles, it is desirable to have means for detecting any particles which may remain to provide a warning should the concentration of those particles exceed a predeter¬ mined level. Similarly, it is desirable to be able to monitor the supplies of process chemicals and process gases used in the industry in the same way. Devices for detecting particles having a diameter of less than 10 microns in fluids with very low flow rates do exist. In one form of device a small quantity of fluid is sampled and passed through a small cross- section passageway. All the particles in the sample are counted by illuminating the sample with a uniform beam of light and detecting light scattered by "each of the particles as they pass through the beam. In order to detect and count the individual flashes of scattered light as each of the particles passes through the beam of light, the passageway must have a very small cross- sectional area (for example 1 to 5 mm2 ) and a very low flow rate of fluid must be used (for example 0.1 litres per minute) , thereby ensuring that only a few particles pass through the beam per unit time. This means, however, that the device cannot, usually, be installed directly in line in a fluid-distribution system carrying a much greater fluid flow-rate of, for example, 15 litres per minute. It must therefore be fitted in a specially constructed branch line and does not then monitor continuously the fluid flowing along the main line. Further, the devices presently available are prohibitively expensive so that, if used at all, only one such device can normally be afforded. When monitoring a large fluid-distribution system it is normally necessary therefore to transfer the device between, several different sampling points so that continuous monitoring at each point is not possible and even a dramatic increase in particle concentration, for example as a result of failure of a filter, may go undetected. According to the present invention there is provided a device capable of detecting individual particles of less than 10 microns diameter in a fluid flowing through the device, the device including a body having a passageway through which, in use, the fluid flows, a light source for directing a beam of light into the passageway and a light detector for detecting 5 scattered light from a small portion only of the cross- sectional area of the passageway, the arrangement being such that light from the light source is unable to pass directly to the light detector.
As the light is detected from a small portion
1.0 only of the cross-sectional area of the passageway, it is possible to detect individual particles even if a large cross-section passageway is used, thereby allowing the device to accommodate a high flow-rate of fluid through the passageway. The device may therefore be interposed 5 in a pipeline in a fluid-distribution system to monitor the fluid flowing through the pipeline continuously without impeding the flow. By detecting light scattered by particles it is able to sense particles of sub-micron size, and because individual particles are detected, it 0 is possible to measure very low concentrations of particles. The device is therefore able to detect very low concentrations of very small particles in fluids flowing through the device at a high rate, and may be used for particle-detection in either liquids or gases, 5 for example deionized water, sea water (for example in the offshore oil industry), aviation fuel, hydrogen fluoride and environmental air.
The small portion of the cross-sectional area of the passageway from which light is detected may comprise less than 5% of the total cross-sectional area of the passageway.
The passageway may have a cross-sectional area of at least 100mm2 enabling high flow rates of liquid to be accommodated.
The light detector may be arranged to detect for¬ ward-scattered light, with its optical axis subtending an angle of less than 90°, and advantageously less than 30 and preferably approximately 25° with the axis of the incident beam of light. Detecting forward-scattered light improves the ability of the device to detect very small particles which scatter only a small amount of light. The light source may be arranged to direct a parallel beam of light into the passageway, and the diameter of the beam is preferably less than 2mm.
Alternatively, the light source may be arranged to bring the beam of light to a focus at a region within the passageway. In an especially advantageous and preferred form of the invention, the light detector includes a light sensor and means for focusing light emanating from the small portion of the passageway onto the sensor. The scattered light will thereby be concentrated on the sensor, greatly increasing the sensitivity of the device. In the case where the beam of light is brought to a focus, the arrangement is preferably such that light scattered from the focal point of the beam is focused onto the light sensor.
The light source may include a laser, and the body may be provided with a first fluid-tight window through which, in use, the beam of light enters the passageway, and a second fluid-tight window through which the light detector receive the scattered light. The output of the light detector may be connected to a signal-monitoring device which may be arranged to provide the same output in response to receipt of a signal from the light detector, regardless of the level of the signal, provided the level is above a predetermined threshold value. This enables the signal monitoring device to produce an output indicative of the number but not the size of the particles in the passageway. The signal-monitoring device may be connected to a counter and/or to an alarm system for providing a warning of the presence of an excessive number of particles, and/or to a printer for providing a permanent record of the output of the monitoring device. The signal-monitoring device may further be connected to a computer for processing the output of the signal-monitoring device.
The present invention further provides a device for detecting particles in a fluid, the device including a body having a passageway through which, in use, the fluid flows, a light source for directing an incident beam of light into the passageway and a light detector for detecting light scattered from a small portion of the passageway, the light detector including a light sensor and a lens for focusing light emanating from the small portion of the passageway onto the sensor, the optical axis of the light detector being angularly displaced from the axis of the incident beam by an amount sufficient to prevent the incident beam from falling directly upon the sensor. The present invention yet further provides a fluid-distribution system including a particle-detecting device as described above and a pipeline for distributing a fluid, the particle-detecting device being interposed in the pipeline so that, in use, all the fluid distributed by the pipeline passes through the device. The system may include a plurality of particle- detecting devices, all of which are connected to a computer for monitoring the number of particles at a plurality of different points around the system. The fluid-distribution system may be a deionised water distributing system.
Furthermore according to the present invention there is provided a method capable of detecting individual particles of less than 10 microns in diameter in a fluid, in which the fluid is caused to flow through a passage¬ way, a beam of light is directed into the fluid in the passageway and light scattered from a small portion of the cross-sectional area of the passageway is detected without detecting the incident beam of light directly.
The small portion of the passageway may comprise less than 5% of the cross-sectional area of the passageway.
The passageway may have a cross-sectional area of at least 100mm2.
The flow-rate of fluid through the passageway may be at least 1 litre per minute.
Forward-scattered light may be detected, with the optical axis of the detected light subtending an angle of less than 90 , and advantageously less than 30°, and preferably approximately 25°, with the axis of the incident beam of light.
By way of example, an embodiment of the invention will now be described with reference to the accompanying drawings, of which:
Figure 1 shows, in perspective, a device for detecting particles in a fluid,
Figure 2 is a cross-section along line II-II of Figure 1 , and
Figures 3a and 3b show, diagrammatically, an optical arrangement incorporated in the device shown in Figure 1.
Referring first to Figs. 1 and 2, the particle- detecting device includes a body member 1 through which there extends a cylindrical passageway 2 having a diameter of 25mm. Extending through the cylindrical wall of the body member 1 are two cylindrical bores 3 and 4. The axes of the bores 3 and 4 are perpendicular to the longitudinal axis of the passageway 2 and they intersect one another at a point midway along the length of the passageway 2 and on the longitudinal axis thereof, where they subtend an angle of 155 . The axes of the bores 3 and 4 are coincident with the line II-II. The body member 1, for example, is constructed in one piece of PVDF.
At the inner end of each bore 3 and 4, there is provided a portion of slightly reduced diameter which forms an inwardly-extending lip 7. Positioned towards the inner end of each bore 3 and 4 to abut the lip 7 is a quartz window 8. The window 8 is urged towards the lip 7 by a hollow clamping screw 9 which engages a screw thread 10 provided at the outer end of each bore 3 and 4. An O-ring 11 is located between the window 8 and the clamping screw 9, and the face of the clamping screw which contacts the O-ring is provided with a bevelled surface 12 which, when the clamping screw is tightened, forces the O-ring outwardly against the inner surface of the respective bore 3 or 4, thereby forming a fluid-tight seal between the window and the bore. The device is capable of withstanding a fluid pressure substantially above ambient pressure and a temperature substantially above a typical ambient temperature (20 C) . In one particular example of the invention the device is capable of operating at a fluid pressure of 70psi (5Xl05N/m2) and a temperature of 70°C.
A light source 13, for example a laser, is attached to the body member 1 at the mouth of the bore 3 and is arranged to direct a narrow, parallel beam of light along the axis of the bore 3 and through the window 8 into the passageway 2 in the body member 1. The light source 13 is provided with an external screw thread 1 which engages the screw thread 10 towards the outer end of the bore 3. A light detector 15 is attached in a similar manner at the mouth of the second bore 4, to detect light passing through the window 8 into the bore. As shown in Figs. 3a and 3b, the narrow beam of light from the light source 13 passes through the first window 8 into the passageway 2. The beam passes approxi¬ mately through the centre of the passageway 2 and is absorbed by the opposite wall. The beam has a diameter D of approximately 1mm and therefore illuminates only a relatively small fraction of the cross-sectional area of the passageway, and none of the incident light passes directly to the light detector 15, due to the offset angle of 25 .
The light detector 15 includes a converging lens 21, and a photocell 22. The lens 21 and the photocell 22 are so arranged that only light emanating from a small portion A of the cross-section of the passageway 2 and passing through the window 8 in the second bore 4 is focused onto the photocell and detected.
The lens 21 and the window 8 have a relatively large diameter in order to collect a substantial proportion of the light scattered from the small portion A, but without collecting any of the incident beam of light.
The small portion A of the cross-sectional area of the passageway which is monitored by the light director 15 coincides with the path of the incident beam of light, and only those particles which pass through the beam in the small portion A are sensed. Since the number of particles which pass through the small portion A per unit time is related to the total concentration of particles in the fluid flowing through the passageway 2, the concentration can be calculated.
The approximate area of the small portion A which is monitored by the light detector 15 is shaded in Fig. 3b and, as can be seen in that figure, its size is determined by the diameter D of the incident beam of light and the field of view F of the detector 15. Only particles which pass through the portion A - i.e. those particles which are illuminated by the beam of light whilst within the field of view of the detector 15 - are detected. In the embodiment of the invention described above the small portion A has a cross-sectional area of approximately 2.4mm2, and the passageway has an area of 500mm2. The small portion A therefore comprises less than \% of the total cross-sectional area of the passageway in this example. However the area occupied by the portion A may in other examples be higher (for example up to 1% or even 5%).
The photocell 22 is provided with an output terminal 23 which is connected to a device (not shown) for monitoring the signals derived from the photocell.
In use the cylindrical body member 1 is connected in-line with a pipe of a fluid-distribution system, so that the fluid distributed by the system flows through the passageway 2 with a high flow rate of, for example between 5 and 50 litres/minute.
If the fluid passing through the passageway 2 carries any particulate matter, light will be scattered from the incident beam whenever a particle passes through it. However, since the light detector 15 is sensitive only to light scattered from the small portion A of the passageway, only those particles which pass through the beam in the small portion A will be detected. Because light is scattered from a particle mostly in a forward direction, and since the window 8 and the lens 21 have a large aperture, the amount of light reaching the photocell 22 will be relatively large, and will depend on, amongst other factors, the size of the particle and the intensity of the incident beam of light.
When light falls on the photocell 22 a voltage pulse is generated which is monitored at the output 23 by the signal-monitoring device (not shown) . The monitoring device senses the voltage pulse and, provided that the amplitude of the pulse exceeds a predetermined discrimin- ation level, produces an output pulse independent of the height of the sensed pulse. When a stream of particles passes through the beam the monitoring device therefore produces a series of identical output pulses, the frequency of which is indicative of the concentration of particles in the fluid having a diameter greater than a predetermined minimum value. The device does not however indicate the actual sizes of the particles.
The monitoring device is connected to an alarm system which provides a warning whenever the particle concentration exceeds a predetermined level, that is whenever the number of received signals per unit time exceeds a predetermined level. The alarm could also be arranged to be triggered by either of the following conditions: (i) a short-term surge of particles of above a certain level is detected, or (ii) the detection rate exceeds the ability of the device to distinguish separate particles. The monitoring device may also be connected to a counter which may have a digital or analogue display, and/or to a printer for providing a permanent record of the particle concentration in the fluid over an extended period of time. The monitoring device may also provide a computer-readable output.
The fluid-distribution system may include several particle-detecting devices positioned at different points around the system for providing a comprehensive particle detection system, and the outputs of the various devices may be connected to a computer for monitoring the particle-concentration at different parts of the fluid- distribution system simultaneously.
The particle-detecting devices may be activated manually, or by a clock, or by flow-sensing devices which activate the particle-detecting devices only when fluid is flowing through them. Alternatively, the devices may be activated by a central computer.
Other embodiments of the device are possible: for example, the cylindrical body 1 may be manufactured from other machinable or mouldable materials, for example polyvinylchloride (PVC), nylon or stainless steel, and the window 8 may be of other transparent materials, for example glass, or, particularly for use with corrosive liquids, sapphire. The O-rings 11 may be manufactured from silicone rubber or fluorine-based rubber, such as that sold under the trade mark "Viton" , or other suitable material.
In another form of the device, the light source 13 is arranged to bring the incident beam of light to a focus at the centre of the passageway 2, and the light detector 15 is arranged to detect only light scattered from the focal point of the incident beam. In this way the size of the small portion of the passageway from which scattered light is detected may be reduced, and the intensity of light in that portion increased, thereby allowing even smaller particles to be detected whilst still using a large passageway to permit a high fluid flow-rate. The light source for the particle-detecting device may include a laser as described or a filament bulb, and the light source may provide visible, infra-red or ultra-violet light. The light source may be located adjacent to the bore 3 or at a remote location, with the light transmitted into the bore by reflection, refraction or by an optical fibre. The light detector may similarly be remotely located and connected to the device by an optical fibre. A light-absorbing device, such as a Rayleigh horn, may be provided to absorb the incident beam after it has crossed the passageway.
The dimensions of the device may vary consider¬ ably from those given in the embodiment described above and in particular, if the device is used for detecting particles in a gas a passageway with a much smaller cross-sectional area may be used. In any case, however, the area of the small portion monitored by the light detector will be very small, for example 10% or less of the cross-section of the passageway.
The photocell 22 in the light detector may be a photo-diode, and may incorporate an operational amplifier to increase the size of the signal delivered to the monitoring device. In order to prevent electrical interference, the light-detector may be provided with mu-metal shielding.
Although the device is capable of accommodating a high flow-rate of fluid through the passageway 2, if it is desired to monitor fluids having extremely high flow-rates such as, for example, aviation fuel being pumped into an aircraft's fuel tanks, the device may be mounted in a by-pass pipe so as to receive only a proportion of the flow of fluid through the main pipeline. In this case, however, the flow rate through the by-pass can still be relatively high, for example 15 litres per minute. The particulate contaminants found in aviation fuel typically have a diameter of between 0.8 and 10 microns.

Claims

Claims :
1. A device capable of detecting individual particles of less than 10 microns diameter in a fluid flowing through the device, the device including a body having a passageway through which, in use, the fluid flows, a light source for directing a beam of light into the passageway and a light detector for detecting scattered light from a small portion only of the cross- sectional area of the passageway, the arrangement being such that light from the light source is unable to pass directly to the light detector.
2_ A device according to claim 1, in which the small portion comprises less than 5% of the total cross- sectional area of the passageway.
3. A device according to claim 1 or claim 2, in which the passageway has a cross-sectional area of at
2 least 100mm .
4. A device according to any one of claims 1 to 3 in which the light detector is arranged to detect forward- scattered light, with its optical axis subtending an angle of less than 30° with the axis of the incident beam of light.
5. A device according to any preceding claim, in which the light source is arranged to direct a parallel beam of light into the passageway.
6. A device according to claim 5, in which the diameter of the beam is less than 2mm.
7. A device according to any preceding claim in which the light detector includes a light sensor and means for focusing light emanating from the small portion of the passageway onto the sensor.
8. A device according to any preceding claim, in which the body is provided with a first fluid-tight window through which, in use, the beam of light enters the passageway, and a second fluid-tight window through which the light detector receives the scattered light.
9. A device according to any preceding claim, in which the output of the light detector is connected to a signal-monitoring device, the signal monitoring device being arranged to provide the same output in response to receipt of a signal from the light detector, regardless of the level of the signal, provided the level is above a predetermined threshold value.
10. A device for detecting particles in a fluid, the device including a body having a passageway through which, in use, the fluid flows, a light source for directing an incident beam of light into the passageway and a light detector for detecting light scattered from a small portion of the passageway, the light detector including a light sensor and a lens for focusing light emanating from the small portion of the passageway onto the sensor, the optical axis of the light detector being angularly displaced from the axis of the incident beam by an amount sufficient to prevent the incident beam from falling directly upon the sensor.
11. A fluid-distribution system including a particle- detecting device as claimed in any preceding claim and a pipeline for distributing a fluid, the particle-detecting device being interposed in the pipeline so that, in use, all the fluid distributed by the pipeline passes through the device.
12. A system according to claim 11 and including a plurality of particle-detecting devices, in which all the particle-detecting devices are connected to a computer for monitoring the number of particles at a plurality of different points around the system.
13. A deionised water distribution system including a particle-detecting device as claimed in any one of claims 1 to 10 and a pipeline for distributing deionised water, the particle-detecting device being arranged to monitor deionised water flowing through the pipeline.
14. A system according to claim 13, in which the particle-detecting device is interposed in the pipeline so that, in use, all the deionised water flowing through the pipeline passes through the device.
15. A method of detecting individual particles of less than 10 microns diameter in a fluid, in which the fluid is caused to flow through a passageway, a beam of light is directed into the fluid in the passageway and light scattered from a small portion of the cross- sectional area of the passageway is detected without detecting the incident beam of light directly.
16. A method according to claim 15, in which the flow-rate of fluid through the passageway is at least 1 litre per minute.
EP19890902396 1988-02-03 1989-02-02 Device and method capable of detecting small particles in a fluid Pending EP0400044A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB8802330 1988-02-03
GB888802330A GB8802330D0 (en) 1988-02-03 1988-02-03 Device & method of detecting small particles in fluid
GB888830023A GB8830023D0 (en) 1988-02-03 1988-12-22 Device and method capable of detecting small particles in a fluid
GB8830023 1988-12-22

Publications (1)

Publication Number Publication Date
EP0400044A1 true EP0400044A1 (en) 1990-12-05

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EP89300997A Withdrawn EP0327353A1 (en) 1988-02-03 1989-02-02 Device and method capable of detecting small particles in a fluid

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EP89300997A Withdrawn EP0327353A1 (en) 1988-02-03 1989-02-02 Device and method capable of detecting small particles in a fluid

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WO (1) WO1989007253A1 (en)

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US4994671A (en) * 1987-12-23 1991-02-19 Schlumberger Technology Corporation Apparatus and method for analyzing the composition of formation fluids
EP0961822A1 (en) 1997-01-16 1999-12-08 Clariant GmbH Fuel-water emulsions
FI108164B (en) 1997-12-23 2001-11-30 Metso Field Systems Oy Optical measuring arrangement
EP1862793A1 (en) * 2006-05-29 2007-12-05 Biotest AG High throughput particle counter

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US3094625A (en) * 1959-11-06 1963-06-18 Cornell Aeromautical Lab Inc Photoelectric apparatus for measuring the size of particles
US3713743A (en) * 1970-11-25 1973-01-30 Agricultural Control Syst Forward scatter optical turbidimeter apparatus
JPS57190249A (en) * 1981-05-19 1982-11-22 Toshiba Corp Measuring method for particle size
JPS59224542A (en) * 1983-06-03 1984-12-17 Hitachi Ltd Measuring device
JPS6011145A (en) * 1983-07-01 1985-01-21 Hitachi Ltd Measuring device of foreign matter
JPS60128331A (en) * 1983-12-16 1985-07-09 Happy Kagaku Kk Dust detecting device

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EP0327353A1 (en) 1989-08-09

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