NZ226897A - Particle monitoring system; results of multiple light scattering analysers collated - Google Patents

Description

226897 Priority Date(s): iO.\ j.

Complete Specification Filed; S Class: £n.Q i 2j/ SS /..

. .Sp. Ih\ 1 .S/,C6 - IA; Publication Date: ..... 2.5.I14R P.O. Journal, No: I<3.'£|r2. .m N.Z. No.

NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION PARTICLE MONITORING SYSTEM We, THE SECRETARY OF STATE FOR DEFENCE IN HER BRITANNIC MAJESTY'S GOVERNMENT OF THE UNITED KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND, a British Corporation Sole of Whitehall, London SW1A 2HB, England, do hereby declare the invention, for which we pcay that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- f t 22B897 iA.

PARTICLE MONITORING SYSTEM This invention relates to a particle monitoring system, in particular a system for monitoring temporal changes in the size and population spectra of particles in a given fluidic environment.

In the context of the present invention, the term 'particles' is intended to apply to both solid bodies and drops of liquid.

Particle analysers are known for example, as described in UK Patent Application No 2022816A in which the size and, to a certain extent, shape of the ambient particles can be determined.

Many such analyers make use of the scattering of light by a particle passing through a beam of radiation. These provide useful data on the properties of particles at a given location.

In the case of airborne particles it is useful to have information on the particlcs at various locations through which the fluid concerned is spread, and particularly to have information as to the change in various properties of the particles, for example size and population, as a function of time.

A present monitoring system is described in UK Application No GB 2132767A which employs a number of monitoring devices set at separate locations and a receiving means to respond to signals from the monitoring devices. The system is more specific to the measuring of water content and has the disadvantage gf not giving any information as to temporal changes in the moisture content of the medium in which the monitoring devices are placed, but merely gives readings taken by the separate monitors over very short periods of time. A further disadvantage of this system is that the monitors themselves cannot store information and so have to be connected up separately to the central receiving unit where the information is stored.

There is therefore a need for a monitoring system for monitoring the properties of individual particles in a fluidic environment and which gives information on the temporal changes of such properties as well as a function of location and which has the added advantage of including remote intelligent monitors.

According to the present invention a particle monitoring system includes a plurality of independent particle monitors spatially separated in conjunction with a master computer, characterised in that each particle monitor employs laser light scattering technique: 22B897 2 detecting and analysing individual particles in its vicinity, and stores the results over a given time period, the storedl results being readable by the master computer for processing functions.

The processing functions may include the representation of the stored results as a function of time and/or location in graphical form.

Thus temporal and spatial changes in various parameters, sucli as size and population of the particles in an environment can be recorded and analysed by the system.

With regard to the individual monitors they may take any suitable form but preferably each comprises a first scattcr chamber including a first concave reflector, a sample of fluid in the form of a laminar flow intercepting at right angles a beam of radiation at the focal point of the first concave reflector, and a second chamber leading from an aperture in the first chamber. Light scattered by the individual particles in the sample is directed towards radiation collectors, converted into electrical signals, and analysed. Such monitors are further disclosed in co-pending New Zealand Patent Specification Nos 226895 and 226896 by the same inventors.

With a number of such monitors spatially separated but operating in synchrony, the behaviour of aerosols in terms of changes in population density, size distribution, and dispersion rates can be analysed as a function time.

The system may have a present alarm capability, so that when the system detects given conditions, an audible or visual alarm is triggered.

An ambodiment of the invention will now be described by way of example only with reference to the accompanying drawings of which Fig 1 is a schematic diagram of the deployment of several Particles Monitors in communication with a Central Master Computer.

Fig 2 is a schematic diagram of a single Monitor.

Fig 3 is a schematic diagram of the electronic processing system. Referring to Figure 1, a number of independent monitors 1 are operated under the control of a central master microcomputer 2. The master microcomputer is typically a 226897 3 commercial microcomputer, such as an IBM-PC or an Olivetti M24, with custom interface electronics. Unlike the monitors (which would be Dattery powered) , the master microcomputer2.requires mains power. In operation, each monitor functions under its own real-time calendar clock. The clocks are used to control the acquisition of data and can be used to initiate a synchronised start between several remote monitors, the start-time having been programmed into the monitor some time earlier. Alternatively a synchronised start can be generated by radio-control or by fibre-optic link3 from the master computer.

When in operation, each monitor-i- draws in ambient air by means of an electric pump, detects and measures each individual particle in the air at high throughput rates by means of laser light scattering, and records the results of each measurement in non-volatile memory.

Each monitor! communicates with the central computer 2_via radio or optical fibre links 3 or- by means of a removeable memory module.

As can be seen from the schematic diagram of a single monitor 1. in Figure 2, an electrically driven pump 4- draws in sample air S from the environment together with sheath air (s through the filter unit 1 . The sheath air b confines the sample air-stream 5 by means of lamina focussing so that it passes accurately through the scattering volume at the focus of the reflector 9* . A laser diode ^ (typically a Philips type 513 CQL) operating at a wavelength of 850nm and a continuous wave power of 20mW produces an output beam (O which is focussed so as to intercept orthogonally the same air-stream 5 at the scattering volume. The cross-section of the beam IO at the intersection point is approximately 3C)imdeep by 4mm across. Particles carried in the sample air-streamS generate scattered light pulses as they pass through the laser beam IO and the reflectors 3 converge this scattered light to light detector points. At these points are placed miniature photomultiplier tube detectors 11 (typically HammamatBU type R632) which convert the optical pulses to electrical pulses which are then directed to the processing electronic circuitry. ;The functional elements of the electronic and computational hardware are depicted in Figure 3. A dual microprocessor system is employed - one committed to data acquisition and recording 12- and the other to system control l2>. In operation, current pulses from the photomultiplier detector 1 1 pass into high-speed digital peak-de* 'A? 0 N 22(5897 4 circuits 14 which output binary values corresponding to the maximum value of the pulses. These binary values are then used as addresses to a look-up table which translates the pulse magnitudes to equivalent particle sizes. Each of the (probably 20) size intervals is represented by a 24-bit counter (ie: 0 to 16 million) and the final output histograms, stored in the memory module, show the values of all counters at the end of each integration period.

The memory module 15 comprises pages of random-access-memory (RAM), each of the 32K bytes, and numbering up to a possible 256 pages. It is anticipated that no more than 16 pages (or 0.5 MBYTES) of RAM will be necessary.

Each monitor is equipped with a simple key-pad and display, so that operational parameters can be entered and results can be observed in the field. The memory module 15 of each monitor 1 is preferably removable so that the data can be returned to the master microcomputer 2 for more detailed processing without disturbing the location of the monitors. Spare memory modules can be plugged into the monitor to continue data collection if required.

The results of the particle detection on each monitor is stored in the form of histograms, each histogram representing the particle size spectrum (ie: number of particles versus size) recorded over a precise time interval or integration period. Associated with each histogram is a time-code and an identity-code for later post-processing use. This integration period is user-definable, and can vary from, say 100ms (allowing 10 histograms to be recorded per second), to several minutes. The data storage capacity of the monitor would normally be sufficiently large to be continuously recorded for a period from minutes up to several hours,the only limit being that of the built-in memory capacity, and the battery capacity.

The monitors are designed to detect individual particles in the range of 1 to 15pm equivalent diameter at maximum rates in excess of 30,000 per second, and to size the particles into a number of size windows, typically of 1pm intervals. Additionally there may be over-range and under-range windows. They collect data over user definable integration period which may be varied from 100ms to 5 minutes, and £Nr store the results in non-volatile memory together with elapsed time^^ and identity codes. They can repeat the previous step continuousAta 22G8 over a defined run-time which may be varied from 1-10,000 integration periodB. The detection run-time of the monitors may be initiated by means of a front-panel switch, a real-time operated delay switch, or, as an optional extra, by remote control using radio or fibre-optic link. The monitors may display on request, using a built-in LCD display, numerical graphical representations of the temporal changes in size spectra recorded over the run-time or any part of the run-time. The monitors are designed to accept user definable alarm conditions and generate an audible (or visual) alarm when these conditions are met. Such conditions may be, for example, a rapid increase in particle count in one or more specified size windows, a particle count which exceeds a pre-specified value, etc. More complex alarm conditions may also be incorporated. For example, the monitor memory could store the size spectrum of a specific aerosol and generate an alarm when the incoming ambient air produces a similar spectrum to within predetermined thresholds. Such conditions would be implemented in software and thus may be modified to suit experimental requirements.

The monitors are also designed to display their current operational status, including overall count rates, battery status, elapsed run-time, specified integration period, alarm conditions in operation etc (to users requirements). The system allows the transfer of recorded numerical data-in the memory module IS to an external printer and also allows it to be removed and interrogated using the remote master microcomputer system.

The nature of the microcomputer system and the post-processing functions it performs could vary for specific experimental conditions, but the functions performed would generally include the following:- The plotting of graphical data representing the change in recorded size spectra from a single monitor as a function of elapsed run-time; the plotting of graphical data representing the change in particle population density in one specific size interval as a function of elapsed run-timej and if data was recorded simultaneously from several monitors placed at specific locations, then graphical data could be plotted representing the change in particle spectra not only as a function of elapsed run-time but also as a function of geographic location. if N X 226897 6 The embodiment of the invention disclosed above relates to the detection and analysis of Airborne particles, but the Particle Monitoring System could work equally well to detect any Fluid-borne particles with some alterations to the optical scattering chamber.

Although this invention has been described by way of example and with reference to possible embodiments thereof, it is to be understood that modifications or improvements may be made without department from the scope of the invention as defined in the appended claims. 226897 7

Claims (18)

CLAIMS vjc. CIQ'im What a.0 olaimod is:-

1. A particle monitoring system including a plurality of independent particle monitors spatially separated in conjunction with a master computer, characterised in that each particle monitor employs laser light scattering tecliniques for detecting and analysing individual particles in its vicinity, and stores the results over a given time period, the stored results being readable by the master computer for processing functions.

2. A particle monitoring system as claimed in Claim 1 characterised in that the processing functions include the representation of the stored result as a function of time.

3. A particle monitoring system as claimed in Claim 1 characterised in that the processing functions include the representation of the stored results as a function of location.

4. A particle monitoring system as claimed in Claim 2 or Claim 3 characterised in that the representation of the stored results is a graphical representation.

5. A particle monitoring system as claimed in Claim 2 or Claim 3 characterised in that the representation of the stored results is by a histogram.

6. A particle monitoring system as claimed in any one of Claims 2 to 5 characterised in that tjje representation is of population density of the individual particles detected.

7. A particle monitoring system as claimed in any one of Claims 2 to 5 characterised in that the representation is of size distribution of the individual particles detected.

8. A particle monitoring system as claimed in any one of Claims 2 to 5 characterised in that the representation is of dispersion rates.

9. A particle monitoring system as claimed in any previous Claim characterised in that each particle monitor includes a remov<xbJe memory module.

10. A particle monitoring system as claimed in any previous Claim characterised in that each particle monitor is equipped with a key pad and visual display unit.

11. A particle monitoring system as claimed in any previous Claim nwv

12. A particle monitoring system as claimed in any previous Claim characterised in that the independent particle monitors act synchronously.

13. A particle monitoring system as claimed in any previous Claim characterised in that the monitors are capable of responding to a predetermined alarm condition.

14. A particle monitoring system as claimed in any previous Claim characterised in that the alarm condition is triggered by the increase in particle count above a predetermined level.

15. A particle monitoring system as claimed in Claim 13 characterised ir that the alarm condition is triggered when a predetermined spectrum is identified.

16. A particle monitoring system as claimed in Claim 16 characterised in that the alarm condition activates an audible or visual alarm or both- one

17. A particle monitoring system as claimed in any/of the preceding claims in which the individual monitors are monitors as described in or claimed in any cluiin of Now Zealand. Patent Specification Hos 226C95 and 226896.

18. A particle monitoring system as herein described with reference to the accompanying drawings. « THE SECRETARY OF STATE FOR DEFENCE IN HER BRITANNIC MAJESTY'S GOVERNMENT OF THE UNITED' KINGDOM OF GREAT BRITAIN AND NORTHERN IRELAND By Their Attorneys HENRY HUGHES LIMITED fi.Z. n.:". i'c.i-.'T OF ^ICE ■12 FEB1991 ft* J S \;i*; C s~>5 C '.J