Apparatus and method for measuring particle concentration of a suspension passing through a sensing zone

Claim 3

The method according to claim 1 wherein said two points are at the same instantaneous amplitude value on the respective leading and trailing edges of each particle pulse, the value at each of the ascertainable points on a given pulse waveform being a predetermined fractional value of the maximum amplitude of that pulse.

Claim 4

The method according to claim 2 wherein said step of ascertaining two points on the waveform of each particle pulse includes the steps of simultaneously applying the particle pulse to a delay circuit and to a stretching and attenuating circuit; delaying the pulse in the delay circuit; stretching the pulse at the maximum amplitude of the pulse; attenuating the stretched pulse to some fractional value of the maximum amplitude; comparing the delayed pulse with the stretched and attenuated pulse; generating a first signal when the instantaneous value of the leading edge of the delayed pulse exceeds the amplitude of the stretched and attenuated pulse; and generating a second signal when the instantaneous value of the trailing edge of the delayed pulse falls below the amplitude of the stretched and attenuated pulse.

Claim 5

The method according to claim 2 wherein said step of measuring durations of pulse segments includes generating duration-measuring pulses each of which has a duration equal to the time between said two ascertainable points and said step of averaging the durations includes the step of integrating said duration-measuring pulses with respecT to time.

Claim 6

The method according to claim 1 wherein the two ascertainable points comprise the peak of each particle pulse and a defined point on one of its leading or trailing edges.

Claim 7

The method according to claim 5 wherein said defined point is a point on the trailing edge and is at an instantaneous value which is a predetermined fractional value of the maximum amplitude of the pulse.

Claim 8

The method according to claim 6 wherein said step of ascertaining two points on the waveform of each particle pulse includes the steps of applying the pulse simultaneously to a differentiating circuit, a comparator, and a pulse stretching and attenuating circuit; differentiating the pulse to ascertain the point of zero slope on the pulse waveform which point is at the peak of the pulse; generating a signal at said point in time when the slope of the pulse waveform is zero; stretching the pulse at the maximum amplitude thereof followed by attenuating the stretched pulse; comparing the stretched and attenuated pulse with the pulse applied directly to the comparator to ascertain when the instantaneous value of the trailing edge of the directly applied particle pulse falls below the amplitude of the stretched and attenuated pulse; and generating a signal at the point in time when the instantaneous value of the trailing edge of the particle pulse falls below the amplitude of the stretched and attenuated pulse.

Claim 9

The method according to claim 1 wherein the two ascertainable points on each particle pulse comprise the point of maximum slope on the leading edge of each particle pulse and the point of maximum slope on the trailing edge of each particle pulse.

Claim 10

The method according to claim 8 wherein said step of ascertaining two points on the waveform of each particle pulse includes the steps of: simultaneously applying the particle pulse to a low threshold circuit and to a differentiating circuit; producing from the low threshold circuit a first signal having a constant given amplitude so long as the amplitude of the particle pulse is above a given threshold; differentiating the particle pulse twice to obtain a signal which is the second derivative of the particle pulse; comparing the second derivating signal with a common potential; generating respective positive and negative signals of given amplitude when the second derivative signal is positive or negative; differentiating said positive and negative signals of given amplitude to obtain positive and negative signal spikes; applying said first signal and said signal spikes to an AND circuit which passes only those signal spikes occurring during the time the amplitude of the particle is above said given threshold; applying the passed signal spikes to a full wave rectifier to obtain only positive spikes, the first and last of which correspond to the respective points of maximum slope on the leading and trailing edges of the particle pulse; and said step of measuring the duration of each pulse segment includes the steps of: applying said first signal of constant amplitude to a trailing edge detector circuit means which produces signal pulses when the amplitude of the particle pulse falls below said given threshold and said first signal is terminated and goes to zero; applying said positive spikes to a first signal generating circuit which is actuated by the first signal spike it receives; generating a first duration measuring signal which has a constant amplitude, which is initiated by the first positive spike and which is not affected by succeeding positive spikes so long as the amplitude of the particle pulse is above said given threshold and said first signal generating circuit has not received a signal pulse from said trailing edge detector circuit means; integrating said first duration-measuring signal; holding the integral signal in a first sample and hold circuit; applying the positive spikes to said first sample and hold circuit; generating an output signal from said sample and hold circuit each time a positive spike iS applied thereto, said output signal having an amplitude equal to the integral of the duration-measuring signal which has been integrated up to that point in time; applying said output signal to a second sample and hold circuit; applying a signal pulse from said trailing edge detector circuit means to said second sample and hold circuit for causing said output signal to be passed through said second sample and hold circuit to a comparator; applying a signal pulse from said trailing edge detector circuit means to a second signal generating circuit to initiate a second duration-measuring signal having a constant amplitude; integrating said second duration-measuring signal; comparing said passed output signal with the developing integral signal of the second duration-measuring signal until said developing integral signal equals the amplitude of said passed output signal; and terminating said second duration-measuring signal when said developing integral signal equals the amplitude of said passed output signal.

Claim 11

Apparatus for measuring particle concentration in a fluid suspension of particles, said apparatus comprising: a particle analyzing device having a sensing zone, means for passing the particles in suspension through said sensing zone, means for sensing the presence of the particles within the influence of the zone and for producing in response to each particle sensed, an electrical particle pulse, said sensing zone having a dimension along the direction of movement of the particles such that the indefinite response regions at the beginning and end of said sensing zone are large compared to the definite response region in the center of said sensing zone, whereby said electrical particle pulses produced have no well-defined ends but have well-defined middle portions, first electrical circuit means for ascertaining two points on the waveform of each particle pulse in the middle portion of the waveform, said points being geometrically defined and spaced apart time-wise second electrical circuit means for measuring the duration of the segment of each particle pulse defined between said ascertainable points and for producing a duration-measuring pulse for each particle pulse, the duration of each duration-measuring pulse being that of said pulse segment and the amplitude thereof being the same for all duration-measuring pulses, and third electrical circuit means for averaging said duration-measuring pulses with respect to time to obtain a signal which is indicative of the concentration of particles in the fluid suspension.

Claim 12

Apparatus for measuring particle concentration in a fluid suspension of particles, said apparatus comprising: a particle analyzing device having a sensing zone, means for passing the particles in suspension through said sensing zone, means for sensing the presence of the particles within the influence of the zone and for producing in response to each particle sensed, an electrical particle pulse, said sensing zone having a dimension along the direction of movement of the particles such that the indefinite response regions at the beginning and end of said sensing zone are large compared to the definite response region in the center of said sensing zone, whereby said electrical particle pulses produced have no well-defined ends but have well-defined middle portions, first electrical circuit means for ascertaining two points on the waveform of each particle pulse in the middle portion of the waveform, said points being geometrically defined and spaced apart time-wise second electrical circuit means for measuring the duration of the segment of each particle pulse defined between said ascertainable points and for producing a duration-measuring pulse for each particle pulse, the duration of each duration-measuring pulse being that of said pulse segment and the amplitude thereof being the same for all duration-measuring pulses, and third electrical circuit means for averaging said duration-measuring pulses with respect to time to obtain a signal which is indicative of the concentration of particles in the fluid suspension.

Claim 13

The apparatus according to claim 10 wherein said first electrical circuit means is operable to ascertain two points having the same amplitude on the particle pulse waveform, one point being on the leading edge of the particle pulse waveform and one point being on the trailing edge of the particle pulse waveform.

Claim 14

The apparatus according to claim 10 wherein said two ascertainable points are at the same instantaneous amplitude value on the respective leading and trailing edges of each particle pulse, the value at each of the ascertainable points on each particle pulse waveform being a predetermined fractional value of the maximum amplitude of that pulse.

Claim 15

The apparatus according to claim 12 wherein said first electrical circuit means includes a delay circuit for delaying each particle pulse, a stretching circuit for stretching each pulse at the maximum amplitude of the pulse, an attenuating circuit for attenuating the stretched pulse to some fractional value of the maximum amplitude of the pulse, and circuit means for comparing the delayed pulse with the stretched and attenuated pulse and for generating a first signal when the instantaneous value of the leading edge of the delayed pulse exceeds the amplitude of the stretched and attenuated pulse and a second signal when the instantaneous value of the trailing edge of the delayed pulse falls below the amplitude of the stretched and attentuated pulse.

Claim 16

The apparatus according to clAim 10 wherein said first electrical circuit means comprises circuit means for producing a stretched pulse, the waveform of said stretched pulse having a flat top, circuit means for adjusting the relative amplitudes of the particle pulse and the flat-topped stretched pulse so that the flat-topped stretched pulse amplitude is a predetermined fraction of the particle pulse, circuit means for adjusting the location in time of the flat-topped pulse relative to the particle pulse so that when the flat-topped pulse is compared with the particle pulse, either the leading edge or the trailing edge of the particle pulse waveform will intersect the flat-top of the waveform of the flat-topped pulse, and means for comparing the particle pulse and the flat-topped pulse to obtain an output signal for the period of time that the amplitude of the particle pulse exceeds the flat-topped pulse, one of the edges of said output signal occurring at the time of intersection and defining said one point.

Claim 17

The apparatus according to claim 14 wherein said first circuit means is operable to ascertain a point on the trailing edge of each particle pulse having an amplitude which is a predetermined fractional value of the maximum amplitude of the particle pulse.

Claim 18

The apparatus according to claim 14 wherein said first circuit means includes a differentiating circuit for differentiating each of said particle pulses to produce for each particle pulse a signal having a zero value at the time of occurrence of the peak of the particle pulse, circuit means for deriving a timing pulse at the time said signal has said zero value and for applying said timing pulse to said second electrical circuit means for causing said second electrical circuit means to generate one clearly defined edge of said duration-measuring pulse, the said one edge of said output signal being applied by circuit means to said second circuit means for causing said second circuit means to generate a clearly defined second edge of said duration-measuring pulse whereby said duration-measuring pulse has a clearly defined leading edge and a clearly defined trailing edge.

Claim 19

The apparatus according to claim 14 wherein said first circuit means is operable to locate said two points on said particle pulse waveform, and said circuit means for adjusting the location in time of the flat-topped pulse relative to the particle pulse is operable to adjust the last two mentioned pulses in such a way that both the leading and trailing edges of the particle pulse will intersect the flat-topped pulse, the two points of intersection defining both said two ascertainable points and respective clearly defined leading and trailing edges of the duration-measuring pulse.

Claim 20

The apparatus according to claim 10 wherein said third electrical circuit means includes circuit means for integrating said duration-measuring pulses with respect to time.

Claim 21

The apparatus according to claim 10 wherein said first circuit means is operable to ascertain for each particle pulse two points comprising a first point at the peak of the particle pulse and a second defined point on either the leading or trailing edge of the particle pulse.

Claim 22

The apparatus according to claim 19 wherein said first circuit means is operable to ascertain said defined point on the trailing edge of the particle pulse, said defined point being at an instantaneous value which is a predetermined fractional value of the maximum amplitude of the particle pulse.

Claim 23

The apparatus according to claim 20 wherein said first circuit means includes a differentiating circuit, a comparator and a pulse stretching and attenuating circuit, conductor means for applying each particle pulse simultaneously to said differentiating circuit, said comparator and said pulse stretching and attenuating circuit, said differentiating circuit being operable to ascertain the point of zero slope on the pulse waveform which point is at the peak of the pulse and for generating a signal at said point in time when the sLope of the pulse waveform is zero, conductor means for applying said generated signal to said second circuit means, said stretching and attenuating circuit being operable to stretch the particle pulse at its maximum amplitude and to attenuate said stretched pulse, said comparator being operable to compare the stretched and attenuated pulse with the particle pulse applied directly to the comparator to ascertain when the instantaneous value of the trailing edge of the directly applied particle pulse falls below the amplitude of the stretched and attenuated pulse and for generating a signal at the point in time when the instantaneous value of the trailing edge of the particle pulse falls below the amplitude of the stretched and attenuated pulse, and conductor means for applying said second signal to said second circuit means.

Claim 24

The apparatus according to claim 10 wherein said first circuit means is operable to ascertain on each particle pulse waveform, two points comprising: a first point at the point of maximum slope on the leading edge of the particle pulse, and a second point at the point of maximum slope on the trailing edge of the particle pulse.

Claim 25

The apparatus according to claim 22 wherein said first circuit means includes differentiating circuit means for deriving the second derivative of the particle pulse and producing a signal having multiple zero crossing points, circuit means for deriving timing signals at the first and last zero crossing points of said signal, said first and last zero crossing points defining said two ascertainable points, and said second circuit means includes other circuit means associated therewith for enabling said second circuit means to generate a rectangular duration-measuring pulse in response to said timing signals for each particle pulse.

Claim 26

The apparatus according to claim 23 wherein said first circuit means includes a low threshold circuit, a differentiating circuit, conductor means for simultaneously applying each particle pulse to said low threshold circuit and to said differentiating circuit, said low threshold circuit being operable to produce a first signal having a constant given amplitude so long as the amplitude of the particle pulse is above a given threshold, said differentiating circuit being operable to produce a signal which is the second derivative of the particle pulse, a comparator for comparing the second derivative signal with a common potential and for generating positive and negative signals of given amplitude when the second derivative signal is positive or negative, circuit means for differentiating said signals of given amplitude to obtain positive and negative signal spikes when said signal changes polarity, conductor means for applying said first signal and said signal spikes to an AND circuit which passes only those signal spikes occurring during the time the amplitude of the particle pulse is above said given threshold, a full wave rectifier circuit for rectifying said signal spikes to obtain only positive spikes the first and last of which correspond to the respective points of maximum slope on the leading and trailing edges of the particle pulse, and said second circuit means includes conductor means for applying said first signal to a trailing edge detector circuit means for producing signal pulses when the amplitude of the particle pulse falls below said given threshold value and said first signal is terminated and goes to zero, conductor means for applying said positive spikes to a first signal generating circuit which is actuated by the first signal spike it receives, said signal generating circuit being operable to generate a first duration-measuring signal which has a constant amplitude, which is initiated by the first positive spike and which is not affected by succeeding positive spikes so long as the amplitude of the particle pulse is above said given threshold and said first signal generating circuit has not received a signal pulse from said trailing edge detector circuit means, an integRator for integrating said first duration-measuring signal, a first sample and hold circuit for holding the integral signal, conductor means for applying the positive spikes to said first sample and hold circuit which is operable to generate an output signal each time a positive spike is applied thereto, said output signal having an amplitude equal to the integral of the first duration-measuring signal which has been integrated up to that point in time, a second sample and hold circuit for holding said output signal, conductor means for applying a signal pulse from said trailing edge detector circuit means to said second sample and hold circuit for causing said output signal to be passed through said second sample and hold circuit to a comparator, conductor means for applying a signal pulse from said trailing edge detector circuit means to a second signal generating circuit to initiate a second duration-measuring signal having a constant amplitude, an integrator for integrating said second duration-measuring signal, a comparator for comparing the passed output signal with said developing integral signal up to the point in time where said developing integral signal equals the amplitude of said passed output signal, and said comparator being operable to generate a cancelling signal and to apply said cancelling signal to said second sample and hold circuit and said second signal generating circuit when said developing integral signal equals the amplitude of said passed output signal for terminating said second duration-measuring signal.

Claim 27

The apparatus according to claim 10 wherein said second electrical circuit means is operable to generate for each particle pulse a rectangular duration-measuring pulse having a given amplitude and a duration equal to the time period between said two ascertainable points.

Claim 28

The apparatus according to claim 10 wherein said particle analyzing device is a Coulter type particle analyzing device and said sensing zone includes a Coulter aperture.