Patent GB-1355215-A (GB)
Title: Axial trajectory sensor for electronic particle study apparatus and method
IPC: G01N15/12
Filed: 1971-10-25
Abstract: 1355215 Particle analysis; pulse discrimiriating COULTER ELECTRONICS Ltd 25 Oct 1971 [27 Oct 1970 24 Dec 1970 8 Feb 1971 9 Feb 1971] 49432/71 Heading H3P [Also in Division G1] The invention relates to the analysis of pulses derived from a Coulter type particle-detector having a relatively long aperture. Desirable PULSES X (Figs. 2, 3) are produced by axial flow particles and they are SELECTED BY the fact that they have a SHORTER DURATION than undesirable pulses Y, Z, derived from particles which pass at an angle or close to the sides of the aperture and thereby pass through non-uniform regions of high current density. Additionally a "low" threshold circuit suppresses noise signals; the input circuit is blocked while a pulse is analysed, Fig. 7 (not shown), the output may be a rectangular pulse having the input pulse peak amplitude, or a delayed version of the original pulse Figs. 9, 10 (not shown); multiple peaks may be detected. Pulse width measurement. Figs. 4, 5.-Graph Fig. 5A shows a desirable pulse 30 and unwanted pulse 34. As is apparent from the circuit, Fig. 4, the pulses are applied (sequentially) to a stretcher 50 producing a "plateau" at peak amplitude X. This is reduced to half height by attenuator 58 and compared at 72 with the delayed original pulse graph C to produce a half-height-duration pulse graph D. This pulse is applied to integrator 72 to produce a ramp with maximum amplitude proportional to the pulse duration, graph F, and if this is less than the level 88, and more than the "noise" threshold 96, gate 144 is opened to pass on a portion of the stretched pulse (graph B) which appears as a rectangular pulse of set width and amplitude X, graph N. The width of this pulse is set by a "strobing" pulse (graph G) from a "one-shot" circuit 112 which is triggered by the trailing edge of the "half-height-duration" pulse graphs D and E; resetting pulses at the end of the cycle are generated similarly. The undesirable pulse 34 which gives rise to a signal 156 in excess of level 88 produces an output from comparator 92 to block the AND gate 120 so that an output pulse is not passed on. Modifications.-Fig. 6 (not shown) the pulse width signal may be provided by gating a clock oscillator instead of integrating as in graph 5F. Figs. 7 and 8 (not shown).-(i) a timing- sequence generator (208) is energized at the end of the "half-height-width" pulse to block further incoming signals until the measurement cycle is completed, (ii) the reference level is reset to the duration of the previous shortest pulse which is stored in a MINIMUM-DURATION-MEMORY-CIRCUIT. This circuit comprises an integrator 260 fed from a constant voltage source 262, so that the reference level drifts up slowly during processing to provide a slight tolerance, but is reset to each duration signal of a lesser level. Reference resetting circuit.-At time t 3  when the duration signal (graph E) has stopped increasing, "one-shot" 220 is triggered to operate AND-gate 240 which shunts a portion of the integrator to reduce the reference level (which is fed back on line 264) until it is equal to the duration signal on line 246. Comparator 248 then shuts the AND-gate 240, leaving the integrator reference level ready of the next measurement. Figs. 9, 10 the output is a delayed version of the input instead of a rectangular pulse. Fig. 11 finds the amplitude of the centre of the pulse, substantially as described in Specification 1,160,026. Figs. 13, 14. The position of the peak is found by differentiating the input pulse, graph 14B (not shown) and the peak amplitude at this position determines the output amplitude. The measuring technique for half-height-duration is substantially as before. Figs. 15, 16, double differentiation is used to detect pulses with multiple peaks which are rejected.