Particle detection

Abstract

Particle detection and characterising apparatus has an insulating tube ( 50 ) along which the particles flow. Five electrodes ( 51, 52, 55, 56 ) and ( 57 ) spaced along the outside of the tube are connected via amplifiers ( 61 ) and ( 62 ) to a processor ( 68 ) arranged to measure the charge on the particles. The apparatus also includes a laser ( 11 ) and photomultiplier tube ( 23 ) arranged to measure the size of the particles so that the nature of the particles can be characterised from their electrical charge and size.

1 . An apparatus for characterizing a particle comprising:
 (a) an electrical charge sensor adapted to determine an electrical charge on the particle; and   (b) an optical device adapted to determine a second characteristic of the particle,   wherein the apparatus is adapted to provide an indication of the nature of the particle according to the charge and the second characteristic.   
     
     
         2 . The apparatus according to  claim 1 , wherein the second characteristic is size. 
     
     
         3 . The apparatus according to  claim 1 , wherein the electrical charge sensor comprises a pathway for the particle and a plurality of electrodes spaced along the pathway arranged to provide an electrical output as the particle passes along the pathway. 
     
     
         4 . The apparatus according to  claim 3 , wherein the pathway is provided by an electrically insulative tube, and wherein the plurality of electrodes are provided on an external surface of the tube. 
     
     
         5 . The apparatus according to  claim 3 , wherein there are five electrodes spaced along the pathway. 
     
     
         6 . The apparatus according to  claim 3 , wherein the outermost electrodes are grounded, wherein two electrodes adjacent to outermost two electrodes are interconnected, and wherein a signal is derived from the difference between the central electrode and the two interconnected electrodes. 
     
     
         7 . The apparatus according to  claim 4 , wherein the tube has an internal diameter of substantially 0.5 mm. 
     
     
         8 . The apparatus according to  claim 4 , further comprising a filter adapted to prevent particles greater than substantially 10 μm from entering the tube. 
     
     
         9 . A method of characterizing a particle comprising:
 (a) measuring charge on the particle;   (b) measuring an optical characteristic of the particle; and   (c) providing an output indicative of the nature of the particle from the combination of both the charge and the optical characteristic.   
     
     
         10 . A method according to  claim 9 , wherein the optical characteristic is indicative of the size of the particle. 
     
     
         11 . An apparatus for measuring a charge on a particle comprising:
 (a) a tube comprising a first end and a second end along which the particle is arranged to flow,   (b) a first and a second outer electrode, wherein the first outer electrode is located adjacent to the first end and the second outer electrode is located adjacent to the second end,   (b) a third electrode adjacent to the first outer electrode and a fourth electrode adjacent to the second outer electrode,   (c) a fifth electrode located between the third and fourth electrodes,   (d) a connection connecting the first and second outer electrodes to ground,   (e) a connection connecting the third electrode to the fourth electrode and connecting the connected third and the fourth electrodes to a measuring circuit, and   (f) a connection connecting the fifth electrode to the measuring circuit, wherein the measuring circuit is adapted to subtract the signals on the third and fourth electrodes from the signal on the fifth electrode to derive a signal indicative of the charge on the particle.   
     
     
         12 . An apparatus for characterizing a particle comprising an electrical charge sensor adapted to determine an electrical charge on the particle, wherein the electrical charge sensor comprises a pathway having at least three electrodes spaced along the length of the pathway comprising a central electrode and two outer electrodes, wherein the two outer electrodes are connected together, wherein a charge signal is derived from the difference between a charge on the central electrode and a charge on the connected two outer electrodes, and wherein the apparatus is adapted to derive an indication of the nature of the particles from the charge signal. 
     
     
         13 . The apparatus according to  claim 12 , further comprising a second device adapted to determine a second characteristic of the particle, wherein the apparatus is adapted to characterize a particle using the combination of both the charge signal and the second characteristic. 
     
     
         14 . The apparatus according to  claim 13 , wherein the second characteristic is size. 
     
     
         15 . The apparatus according to  claim 13 , wherein the second device is an optical device. 
     
     
         16 . An apparatus for characterizing a particle in a tube comprising
 (a) a plurality of electrodes space along the tube and adapted to determine an electrical charge on the particle, and   (b) a second device adapted to determine a second characteristic of the particle unrelated to the electrical charge,   wherein the apparatus is adapted to provide an indication of the nature of the particle using a combination of both the charge and the second characteristic.