BS 5540-6:1990

For instruments working on the light obscuration principle.

This Part of BS 5540 describes a method for the calibration of liquid automatic particle counters (APCs) working on the light obscuration principle. It establishes a uniform and precise method of calibrating these instruments which will enhance the degree of reproducibility of particle count data between laboratories.

The calibration material used is mono-sized latex spheres whose size can be verified by a number of different methods. The particle size parameter reported is the equivalent optical diameter based upon the projected area of a spherical particle.

The method described first confirms the maximum concentration limits of the instrument being calibrated, verifies the particle size distribution of the latex spheres and, finally, enables the instrument to be calibrated in an accurate and precise manner.

The calibration curve of an APC is the reference that relates the particle size to the electrical threshold settings of the instrument. The development of the calibration curve is of primary importance in establishing the accurate sizing of particles being counted. A procedure is described that enables the voltage threshold value for any particle size within the sizing range of the sensor to be obtained.

This method is intended for application to any APC working on the light obscuration principle in which particles interrupt the passage of light from a source to a detector. It assumes that the counter is equipped with at least two channels with adjustable voltage thresholds.

Although this Part of BS 5540 is intended for fluid power applications, it may also be applicable to other fields where this method of calibration is considered appropriate.

NOTE The titles of the publications referred to in this standard are listed on the inside back cover.