A NEW METHOD FOR THE EXACT DETERMINATION OF THE FALSE COUNT RATE OF OPTICAL-PARTICLE COUNTERS

The false count rate is a measure for the influence of disturbances on optical particle counters. It gives the number of measured false puls es referring to a known time period. The false count rate of each part icle counter must be known, because the false pulses falsify the resul t of measurement so heavily at low particle concentrations, that no st atements can be made about the real particle number concentration. Pre vious methods determining the false count rate [3 to 6] were connected with highly technical expense and highly statistical uncertainties. F or the determination of the false count rate the methods require absol utely particle free air, so the counts of the particle counter are int erpreted as false pulses. However this is technically difficult to ach ieve.In order to reach the postulated condition approximately, the air must be filtered very carefully with highly technical expenditure. So the determination of the false count rate is connected with a high ex penditure. Another method [5, 6] makes use of the statistical characte ristics of the appearance of disturbing pulses to detect false counts, but it includes statistical uncertainties. With the new method the co unted pulses can definitely be assigned to a particle or to a disturba nce. This is possible, because the signal spectrum of the particle pul ses and the disturbing pulses are so different, that they can be disti nguished visually in an easy way. Each signal spectrum can be examined , because there are only a few pulses to expect. With this method a fi nite particle concentration in the air is allowed and the great effort to filter the air is not required. With this method it is possible to determine the false count rate exactly and directly on the spot.