GB1105604A - Determining the concentration of particles suspended in air - Google Patents

Abstract

1,105,604. Measuring particle concentration. A.E. CASWELL. June 21, 1965 [April 25, 1964], No. 17229/64. Heading G1N. In a cell measuring the concentration of particles in air (or a gas), the air is drawn through a cleaning filter gauge 2, ionized by a radio-active source 4, and blown through a conductive tube 6 set in an insulating wall 7 into a charge chamber 5, the tube 6 being held at a potential of, for example, +600v so that substantially all the negative ions in the air are attracted towards the tube 6 and are then swept through it into chamber 5 to set up a unipolar ion plasma in the charge chamber 5; the particles then being charged by collision with these ions and passing to a collector electrode 11 which is connected to an electrometer 13 measuring the total change on these particles. The negative ions but not the particles are prevented from reaching the collector 11 by a screen gauge 10 held at a potential of, for example, +60v. The screen potential is chosen with regard to the different mobilities of the ions and the particles. The collector may consist of two concentric cylinders held at different potentials, the charge on them being conveyed to the electrometer by means of a spring-loaded plunger 14. The geometry of the cylinder and of the supporting chamber, the velocity of the air, and the relative potentials of the cylinders, are varied to ensure that particles within a given range of size are "collected". The collector, alternatively, may consist of steel wool, or of parallel plates. An airflow regulating device is described which may be used to ensure a constant air pressure at the input to the ionization chamber of the apparatus.