Optics: measuring and testing – By particle light scattering – With photocell detection
Reexamination Certificate
1999-08-20
2001-01-23
Font, Frank G. (Department: 2877)
Optics: measuring and testing
By particle light scattering
With photocell detection
C356S337000, C356S339000, C356S342000
Reexamination Certificate
active
06177994
ABSTRACT:
This invention relates to an improved apparatus and method for measuring particle size distribution,
It is known to provide particle size distribution analysis apparatus which rely on the scattering of light incident upon a sample of particles and have multiple laser sources at different angles relative to a cell containing the sample. An example of such a system is shown in EP 0 559 529 wherein a further beam of laser produced light is introduced by an optical fibre at an angle to the main laser beam. In such systems the minimum size of particle which can be detected is reduced by transforming the information from the extra, angled, lasers in to further angular information. It is also known to introduce an extra light source and filter to achieve further information as shown in U.S. Pat. No. 5,164,787.
It will be appreciated that the term particle may mean any phase of a discontinuous material contained within a continuous phase of a supporting medium. Either phase may be gaseous, liquid or solid. The only physical limitation is that the particle must have a different refractive index to the medium and further, that the medium must be substantially transparent at any illuminating wavelength of light.
According to a first aspect of the invention there is provided a particle size distribution analysis apparatus wherein there are provided a sample measurement zone adapted to define a sample of particles, a light emitting means adapted to provide a source of light incident upon the measurement zone, and a detection means adapted to measure light levels at different scattering angles and to output signals to a computation means, enabling the size of particles contained win the sample to be determined, wherein the light emitting means comprises a first light source emitting a substantially monochromatic first wavelength of light and a second light source emitting a substantially monochromatic second, different, wavelength of light.
An advantage of such a system is that the range of particle sizes which can be determined by the calculation means is increased over a system with only a single light source.
In the preferred embodiment at least the first source is a laser, possibly a He/Ne laser and preferably a red light laser.
Preferably at least the second light source is an LED (light emitting diode). This has the advantage that a cheap and robust light source is. provided which has a longer life than other light sources, is physically small, and does not produce a large amount of heat.
In another embodiment at least the second light source may be a laser diode.
Some prior art systems have provided a plurality of light sources. However, such prior an systems have tended to use a second source which was not mono-chromatic, for example a tungsten halogen source. The provision of such a light source is disadvantageous because it is bulky, does not have a long life, produces a large amount of heat, must be left energised for long periods to ensure thermal equilibrium is achieved and for application to the arrangement of the present intention would require filtering means to ensure that only a substantially monochromatic light were output.
The second light source may output light with a wavelength substantially in the range 350 nm to 550 nm. The second light source may output light with a wavelength substantially in the range 400 nm to 500 nm and possibly the second light source may output light with a wavelength of substantially 466 nm. The skilled person will appreciate that in the preferred embodiment the second light source should output light with as small a wavelength as possible but that practical considerations may mean that a compromise wavelength is used. Such considerations include cost of manufacture, availability of suitable light sources, the stability of available sources, etc.
The second light source may emit light that is monochromatic enough so that it does not need filtering to achieve analysable scattering results (i.e. no monochromatic filter may be provided). Alternatively, for some applications we may provide a filter.
The first light source may output light with a wavelength substantially in the range 533 nm to 2 &mgr;n. The first light source may output light with a wavelength substantially in the range 583 nm to 683 nm and in one embodiment the first light source may output light with a wavelength of substantially 633 nm. The skilled person will appreciate that the choice of wavelength of the first light source may be influenced by practical considerations.
The light sources may emit light with wavelengths differing by substantially 170 nm or may be by substantially 300 nm, 250 nm, 200 nm, 150 nm, 100 nm or 50 nm. However, the skilled person will appreciate that the it is desirable to have a larger wavelength difference than this and also that the device may well work with a wavelength difference smaller than this.
Preferably the light sources are arranged so that beams of light emitted substantially superpose (or substantially superimpose) one another on the measurement zone. This has the advantage that the structure of the apparatus is simplified.
The second light source may be arranged so that a beam of light that it emits is inclined at an angle to a beam of light emitted from the first light source. Again, this has the advantage that the structure of the apparatus is simplified. The second light source may be arranged at an angle substantially in the range 0° to 30° to the beam of light emitted from the first light source. The second light source may be arranged at an angle substantially in the range 10° to 20°. In the most preferred embodiment the second light source may be arranged at substantially 10° to 15°, most preferably at 15°±1°.
It is advantageous to allow the second light source to pass directly through the sample by inclining the beam at an angle to the beam emitted from the first light source as this means that no beam splitter is required, thus simplifying the optical components of the system.
Preferably light emitted from the second light source and the optical axis of the first light source lie in a plane which is inclined at an angle &phgr; to a plane in which the detection means (which may include a large angle detector, a forward angle detector, a focal plane detector, s back scatter detector) is situated. Preferably the angle &phgr; is substantially a right angle. For the avoidance of doubt this is illustrated in
FIG. 1
of the accompanying drawings wherein the optical axis of the first light source is along the z axis, light emitted from the second light source is inclined at angle &phgr; to the z axis in the yz plane and wherein the detection means is provided in the xz plane.
The second light source may be adapted, in use, to be pulsed. This has the advantage that the signal to noise ratio of the system may be increased and also the peak intensity of the system may be increased.
At least one light output stabilisation means may be provided to ensure that the light emitted from either (or both) of the light sources is constant. Preferably a first light source stabilisation means is provided to monitor the first light source and/or an a second light source stabilisation means is provided to monitor the second light source.
The stabilisation means may comprise a primary monitoring means and primary processing means. The processing means may be connected in a closed loop which uses the detected signal from the primary monitoring means to control the output power of the light emitted from the respective light source. Alternatively, or additionally, instead of controlling the output of the light source to be stable we may allow it to fluctuate and the primary processing means may output a signal representative of the light power emitted from the respective light source to enable provision for fluctuations in the light power emitted from the light source in subsequent calculations relating to the particle sizes.
One of tie light sources may have the processing means connected to a closed loop in order to control the output power of
Catterall Clive Patrick Ashley
Stephenson Duncan Edward
Watson David John
Cooper & Dunham LLP
Font Frank G.
Malvern Instruments Limited
Nguyen Sang H.
White John P.
LandOfFree
Relating to the measurement of particle size distribution does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Relating to the measurement of particle size distribution, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Relating to the measurement of particle size distribution will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2473737