| 摘要 |
1385363 Particle analysis COULTER ELECTRONICS Ltd 24 April 1972 [28 April 1971 4 Jan 1972] 18899/72 Heading G1N [Also in Division H3] The invention relates to apparatus for monitoring pulses from Coulter type apparatus to determine particle concentration in a fluid suspension. Since the pulses have no well-defined ends the duration of a defined part from the middle of pulse is monitored and these durations are averaged. The part of the pulse chosen may be:- (i) the width at half peak amplitude, (ii) the peak to half amplitude width or (iii) the first point of inflection to the last point of inflection, (i.e. about half-way up the flanks of the pulse). In arrangement (i) Figs. 3A, 3B (not shown) the delayed pulse is compared with a half-height plateau by techniques as described in Specification 1355215 and the width signals are arranged e.g. by a well-damped meter or timed integration Fig. 4, (not shown). Arrangement (ii) Figs 5A; SB (not shown) the peak height position is found by differentiation in one channel to set a flip-flop, and the fall to half amplitude as previously in a parallel channel resets the flip-flop. In this arrangement the differentiator drives a saturable amplifier to produce a square wave (H) which is further differentiated to produce a spike (I) at the peak position. In arrangement (iii) Figs. 6A, 6B (not shown), which may handle compound pulses (such as 6-21), the points of inflection are found by double differentiation (graph D) and pin pointed by squaring and differentiating (E), (F). A time (or width) signal is provided by an integrator generating a ramp output (J) started by the first inflection pulse. Subsequent inflection pulses set the ramp amplitude into a pair of series-connected sample-and-hold circuits and step the values forward. Thus when the pulse ends, as determined by the low-threshold signal (B), the last stored value will be that at the zero point of the pulse, and the required value will be the last but one signal held in the second sample-and-hold circuit. An alternative and more complex way of doing this is disclosed with reference to Figs. 8, 9A, 9B (not shown). The double differentiated signal (F) is added to the low-threshold signal (I) to produce a stepped wave (J) from which the points of inflection (where it crosses the zero line) are more easily determined. In another channel the original pulse is clamped and delayed by an amount equal to that unavoidably introduced in the differentiating channel, whereby the pulse amplitude at the point of inflection can be stored to compare with the trailing pulse flank. |
