Apparatus and method for determining the average amplitude of a plurality of randomly occurring electrical pulses

摘要

1,145,781. Measuring mean size of particles; pulse amplitude measurement. COULTER ELECTRONICS Ltd. March 18, 1966 [March 22, 1965], No. 12177/66. Headings G1N and G1U. [ Also in Division H3] The mean size of particles (e.g. blood corpuscles) passing through a Coulter detector is automatically derived by a circuit which stretches each pulse into the next succeeding pulse to form a monopolar signal of substantially histogrammic configuration, the levels of which are proportional to the sizes of the respective particles giving rise to them, and the monopolar signal is averaged to provide an indication of the mean particle size. In order to allow for coincidences (two or more particles passing at the same time through the aperture) which would tend to make the measurement too high, part of each level of the histogrammic signal may be removed. As shown in Fig. 11, a string of pulses from a Coulter detector 130 are amplified and a capacitor C in a memory circuit 144 successively stores the peak value of each pulse to form the histogrammic signal which is then amplified and integrated over a given time. The arrival of each pulse is detected by an adjustable low threshold circuit 87 which triggers a shorting circuit 110 to discharge the capacitor C which is then charged to the peak voltage of the pulse. A leading edge detector 93 triggers a monostable multi-vibrator 156 which controls the switching of a diode in a loading stage 200 to correct the histogrammic signal for coincidence. The loading signal may instead be applied to the integrator 202 or amplifier 150. Two embodiments without coincidence correction are described. In one, Fig. 2 (not shown), two memory circuits are provided, the second one retaining the peak voltage of the latest pulse during the time interval between the discharging of the first capacitor and its subsequent charging to the peak voltage of the next pulse. In the other arrangement, Fig. 5 (not shown), only one memory circuit is provided and a normally open switching circuit (142) connects the Coulter detector (130) to the memory circuit (144) for a small time interval at the peak of each pulse.