U.S. patent number 3,867,613 [Application Number 05/302,810] was granted by the patent office on 1975-02-18 for particle counting apparatus.
This patent grant is currently assigned to Minnesota Mining and Manufacturing Company. Invention is credited to David J. Schoon.
United States Patent |
3,867,613 |
Schoon |
February 18, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Particle counting apparatus
Abstract
A particle detection apparatus for determining the number and
size of particles present in a plurality of particles dispersed
over a field uses an oscillating mirror and movement of the field
transversely to the mirror movement to optically scan the field
with a succession of scan cycles. Particle indicating signals are
produced each time a particle scanned satisfies intensity and size
thresholds. Only one particle indicating signal for a particle is
used to produce a count signal. Particle indicating signals
developed by scans other than the scan from which a count signal
for the particle is developed are suppressed. This is accomplished
by circuitry including a coincidence circuit and a memory provided
by a shift register circuit controlled by a selected number of
clock pulses provided for each scan cycle. A feedback circuit is
connected to respond to the initiation of a particle indicating
signal to assure continuation of the particle indicating signal for
the remainder of the time such scan intercepts the particle. The
feedback circuit is also connected to respond to the output of the
shift register circuit to improve the operation of the circuitry
providing for suppressing the signals developed by scans of a
particle in excess of the one needed for a count signal. A meter
reading is provided which is indicative of the number of particles
intercepted when scanning with the field in a selected position to
enable the operator to set the intensity threshold correctly.
Inventors: |
Schoon; David J. (Saint Croix,
MN) |
Assignee: |
Minnesota Mining and Manufacturing
Company (St. Paul, MN)
|
Family
ID: |
23169301 |
Appl.
No.: |
05/302,810 |
Filed: |
November 1, 1972 |
Current U.S.
Class: |
377/10; 356/335;
377/54 |
Current CPC
Class: |
G06M
11/00 (20130101) |
Current International
Class: |
G06M
11/00 (20060101); G06m 011/04 () |
Field of
Search: |
;250/222PC ;356/102
;235/92PC,92SH,92CA ;350/6 ;340/146.3F |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Shaw; Gareth D.
Assistant Examiner: Thesz, Jr.; Joseph M.
Attorney, Agent or Firm: Alexander, Sell, Steldt &
Delahunt
Claims
1. Particle detection apparatus for determining the number of those
particles having a predetermined size that are present in a
plurality of particles dispersed over a field comprising:
scanning means for scanning said field using a succession of scan
cycles, each of said scan cycles moving across said field for
successive scanning of each particle presented to the scan cycle,
said scanning means providing a particle indicating signal each
time a particle having a predetermined size is scanned and
supplying a synchronizing pulse at the beginning of each scan
cycle;
a clock pulse generator connected to said scanning means for
receiving said synchronizing pulse and supplying a selected number
of clock pulses in response to said synchronizing pulse and at a
rate causing the last of said clock pulses to occur prior to
completion of a scan cycle;
a scan cycle memory including a shift register having a clock
input, a data input and an output, said shift register requiring
said selected number of clock pulses for a cycle of operation, said
clock input connected to receive said clock pulses, said data input
connected to serially receive each of said particle indicating
signals developed by said scanning means, said shift register
entering a particle indicating signal when present at said data
input while one of said clock pulses is present at said clock input
and shifting said entered particle indicating signal to said output
upon subsequent receipt by said clock input of clock pulses equal
to said selected number; and
a signal coincidence circuit for presenting a count signal in
response to a first signal unless a second signal is received by
said signal coincidence circuit during said first signal, said
signal coincidence circuit connected to said scanning means to
receive said particle indicating signals from said scanning means
as one of said first and second signals and connected to said
output of said shift register to receive said particle indicating
signals from said shift register output as the other
2. A particle detection apparatus in accordance with claim 1
wherein
said one of said first and second signals is said first signal and
said
3. A particle detection apparatus in accordance with claim 1
wherein
said one of said first and second signals is said second signal and
said
4. A particle detection apparatus in accordance with claim 1
wherein
said scan cycle includes a scan in one direction across the field
and a scan in the opposite direction across the field with the last
one of said selected number of clock pulses for a scan cycle
produced prior to the
5. A particle detection apparatus in accordance with claim 1
wherein said scan cycle includes a scan in one direction across the
field and a scan in the opposite direction across the field with
the last one of said selected number of clock pulses for a scan
cycle produced shortly before completion of said scan in said
opposite direction across the field, said apparatus further
including a divider circuit connected to said signal coincidence
circuit for providing one count signal for every two of said count
signals
6. A particle detection apparatus in accordance with claim 1
wherein the frequency of said scan cycles relative to the rate at
which said clock
7. A particle detection apparatus in accordance with claim 1
wherein said clock pulse generator includes means for adjusting the
rate at which said clock pulses are produced to establish the
frequency of the scan cycles relative to the rate said clock pulses
are produced for determining the point in a scan cycle when the
last one of said selected number of clock
8. A particle detection apparatus in accordance with claim 1
wherein said scanning means includes
a light responsive device;
a source of light;
means establishing an optical path between said light responsive
device and said light source with the field positioned in said
optical path including an oscillating mirror disposed between said
field and the light responsive device for scanning back and forth
across the field in one direction;
a mirror control circuit having means operatively coupled to said
mirror to sense the position of said mirror and drive said mirror
for oscillation at a selected frequency and
means for moving the field transversely to the movement of said
mirror whereby a sinusoidal optical scan of the field is presented
to said light responsive device when the mirror is oscillating in
said one direction
9. A particle detection apparatus in accordance with claim 8
wherein said mirror control circuit includes a pulse forming
circuit connected to said clock pulse generator for providing a
pulse at the beginning of each scan
10. A particle detection apparatus according to claim 1 wherein
said scanning means includes circuitry for establishing the minimum
light intensity that a particle must present when scanned before
said particle indicating signal can be produced; and a feedback
circuit connected between the output and input of said circuitry
for reducing the minimum light intensity requirement for the scan
portion remaining for a particle being scanned once said particle
indicating signal for such particle is
11. A particle detection apparatus according to claim 10 wherein
the output
12. A particle detection apparatus according to claim 1 wherein
said scanning means includes circuitry for establishing the minimum
size that a particle must present to a scan before said particle
indicating signal can be produced; and a feedback circuit connected
between the output and input of said circuitry for reducing the
minimum size requirement for the scan portion remaining for a
particle being scanned once said particle
13. A particle detection apparatus according to claim 12 wherein
the output
14. A particle detection apparatus according to claim 1 wherein
said scanning means includes circuitry having a minimum intensity
circuit for establishing the light intensity that a particle must
present when scanned before said particle indicating signal can be
produced and a minimum size circuit for establishing the minimum
width of a particle that must be scanned before said particle
indicating signal can be produced; and a feedback circuit connected
between the output of said circuitry and the input of said minimum
intensity circuit back minimum size circuit for reducing the
intensity and size requirements for the scan portion remaining for
a particle being scanned once said particle indicating
15. A particle detection apparatus according to claim 14 wherein
the output
16. A particle detection apparatus according to claim 1 wherein
said scanning means includes a feedback circuit with the output of
said shift register connected to the input of said feedback circuit
and said synchronizing pulse provided by said scanning means is
applied as a clock pulse to said shift register to shift the shift
register one clock pulse causing the output of said shift register
to be applied to said feedback circuit earlier in each scan
subsequent to that first scan of said field.
17. Particle detection apparatus for determining the number and
size of particles present in a plurality of particles dispersed
over a field including:
scanning means for scanning the field using a succession of scan
cycles wherein each scan cycle proceeds across the field at a
non-linear rate, said scanning means providing a signal each time a
particle in the field is scanned, said signal having a duration
dependent on the rate of scan and the width of the particle
presented to the scan;
said scanning means including a control circuit for providing a
signal having a non-linear rate corresponding to the non-linear
rate of the scan cycle;
signal processing circuitry connected to said scanning means for
receiving said first-mentioned signal to provide a particle
indicating signal when said first-mentioned signal has a
predetermined amplitude and duration;
said signal processing circuitry including a minimum size circuit
having an integrating circuit portion for producing a signal
indicative of the duration of said first-mentioned signal, said
integrating circuit portion connected to said control circuit for
receiving said signal provided by said control circuit for
controlling the operation of said integrating circuit whereby said
signal indicative of the duration of said first-mentioned signal
provided by said integrating circuit portion is
18. Particle detection apparatus, which scans a field containing a
plurality of particles and produces particle indicating signals in
accordance with the size of the particles scanned and the light
intensity received from the particles scanned relative to an
adjustable intensity threshold, comprising:
means for enabling scanning to occur back and forth on a line
across an operator selected portion of the field causing particle
indicating signals to be produced;
means connected to said first-mentioned means for providing a pulse
signal for each particle indicating signal produced when scanning
said operator selected portion;
means connected to said second-mentioned means, including a display
means responsive to said pulse signals for providing a single
visual indication which varies in proportion to the number of said
pulse signals received whereby the intensity threshold can be
varied until said single visual indication indicative of the
receipt of the maximum number of said pulse
19. A particle detection apparatus according to claim 18 wherein
said second mentioned means is a circuit responsive to the leading
edge of the
20. A particle detection apparatus according to claim 18 wherein
said second mentioned means is a circuit responsive to the trailing
edge of the
21. A particle detection apparatus according to claim 18 wherein
said last
22. Particle detection apparatus for determining the number of
those particles having a predetermined size that are present in a
plurality of particles dispersed over a field comprising scanning
means for scanning said field in a succession of scan cycles and
including circuitry for establishing the minimum size that a
particle must present before a particle indicating signal can be
produced and a feedback circuit connected between the input and
output of said circuitry for reducing the minimum size requirement
for the scan portion remaining for a particle being scanned once
said particle indicating signal for such particle is
23. Particle detection apparatus for determining the number of
those particles having a predetermined size that are present in a
plurality of particles dispersed over a field comprising scanning
means for scanning said field in a succession of scan cycles and
including circuitry for establishing the minimum light intensity
that a particle must present before a particle indicating signal
can be produced and a feedback circuit connected between the input
and output of said circuitry for reducing the minimum light
intensity requirement for the scan portion remaining for a particle
being scanned once said particle indicating signal for such
24. Particle detection apparatus for determining the number of
those particles having a predetermined size that are present in a
plurality of particles dispersed over a field comprising scanning
means for scanning said field in a succession of scan cycles and
including circuitry having a minimum intensity circuit for
establishing the light intensity that a particle must present when
scanned before a particle indicating signal can be produced and a
minimum size circuit for establishing the minimum width of a
particle that must be scanned before said particle indicating
signal can be produced; and a feedback circuit connected between
the output of said circuitry and the input of said minimum
intensity circuit and siad minimum size circuit for reducing the
intensity and size requirements for the scan portion remaining for
a particle once said particle indicating
25. A particle detection apparatus according to claim 24 wherein
said apparatus includes a scan cycle memory having its input
connected for receiving said particle indicating signals and having
its output connected to said feedback circuit, the output of said
memory being indicative of the particle indicating signals produced
during the preceding scan cycle.
26. A particle detection apparatus according to claim 25 wherein
said scan cycle memory includes a shift register.
Description
Field of the Invention
The invention presented herein relates to particle detection
apparatus using a line by line scan of a field for counting
particles in the field which are at least of a predetermined size
with provision made to compare a scan line with a prior scan line
to prevent multiple counts for a single particle.
BACKGROUND OF THE INVENTION
The fields of biology, medicine, photogrammery, metallurgy,
pollution control, pharmaceutical manufacture and many others
require apparatus for automatically sizing and counting various
particles or objects.
A few instruments are presently available which provide such
counting and sizing with varying degrees of accuracy. Those
instruments capable of providing a fair degree of accuracy are very
expensive. In order that the use of apparatus of this type can
expand, there is need for an accurate and flexible particle
measuring apparatus that can be sold for a more reasonable amount.
Presently known apparatus use designs which require costly major
components.
DESCRIPTION OF THE PRIOR ART
Automatic examination of particles randomly distributed over a
field has been accomplished by scanning the field by a light beam.
For example, a light spot scan developed on the screen of a cathode
ray tube which is imaged upon the field has been used. The
intensity of light passed through or reflected by the field which
varies in accordance with the particles present in the field is
measured by a photomultiplier tube. A vidicon tube has also been
used by focusing the field carrying particles on the screen of the
tube which is then scanned by an electron beam. However, any
scanning arrangement using cathode ray tubes or vidicon tubes is
expensive, bulky and presents maintenance problems which can be
handled only by specially trained personnel.
Some particles overlap several lines of scan causing a change in
the output of the photomultiplier for each interception. It was
recognized that some form of line to line memory was needed so the
signal output for a given line scan could be compared with a
representation of the signals generated one line previously with
provision made to suppress signals when correspondence of the
signals was found to prevent multiple counts of a particle.
Magnetic drum and tape recording arrangements have been used as
well as delay lines to provide a memory for counting apparatus. The
magnetic recording approach is very expensive, bulky and presents
maintenance problems. Delay lines are not adjustable which requires
the sanning frequency to be precisely matched to the fixed time
delay provided by a delay line. In addition, delay lines are
temperature sensitive, provide poor resolution and are
expensive.
Accurate intensity threshold adjustment of automatic counting
apparatus is essential to prevent erroneous counts due to the
apparent bridging between particles that can occur when the
particles are not clearly defined. Prior art counting apparatus
includes the use of a television type display developed by scanning
a field which the operator visually compares with the actual field
to obtain an adjustment of the threshold levels. Such an
arrangement for making the threshold adjustments is expensive and
requires a great deal of judgment on the part of the operator.
Another approach to adjustment of the threshold levels requires a
physical count of the particles by the operator which is compared
with the apparatus count. This is time consuming and subject to
operator error.
SUMMARY OF THE INVENTION
The invention presented herein uses an oscillating mirror scanning
arrangement with a photomultiplier detector which is considerably
less expensive and presents less complex maintenance problems than
the cathode ray tube and vidicon tube scanning systems employed in
prior known automatic particle counting apparatus. An oscillating
mirror positioned in an optical path scans back and forth across
the field containing the particles to be detected while the field
is moved transversely to the mirror scan to provide a sinusoidal
raster type scan of the field. The light intensity from the scanned
field varies in accordance with the particles in the field and is
detected by a photomultiplier tube, the output of which is
processed via minimum intensity and size threshold circuits to
provide particle indicating signals.
The use of delay lines or magnetic recording arrangements to
provide the scan to scan memory needed for an automatic particle
counting apparatus has also been avoided by this invention. A shift
register circuit is used to provide the memory. In addition to
providing a less costly memory with excellent resolution, the use
of a shift register circuit does not place any limitation on the
scan frequency used. A synchronizing pulse obtained from the
oscillating mirror indicative of the beginning of each scan cycle
is applied to a clock pulse generator causing it to initiate a
selected number of clock pulses for each scan cycle. The shift
register circuit uses the selected number of clock pulses for a
cycle of its operation. The clock pulses control the response of
the shift register circuit to particle indicating signals applied
to its input to provide a memory for use in comparing the particle
indicating signals produced during one scan with the particle
indicating signals present during the preceding scan so only one of
all the signals generated for a given particle detected will be
used to provide a count signal. The shift register circuit receives
each particle indicating signal and for each one received provides
a particle indicating signal at its output after the shift register
circuit has received the number of clock pulses required for one
cycle of operation. A particle indicating signal at the output of
the shift register circuit during a current scan indicates a
particle indicating signal was received by the shift register
circuit the selected number of clock pulses earlier during the
preceding scan. A signal coincidence circuit, which presents a
count signal in response to a first signal unless a second signal
is received by the coincidence circuitry during the first signal,
is connected to receive the particle indicating signals obtained
from processing the output of the photomultiplier as one of the
first and second signals with the particle indicating signals from
the shift register circuit providing the other of the first and
second signals.
A synchronizing pulse developed from the oscillating mirror is
supplied to the clock pulse generator at the beginning of each scan
cycle so long term drift of the scanning frequency as determined by
the oscillating mirror and/or the clock pulse generator frequency
is permissible without introducing any erroneous counts. This is a
most desirable feature since absolute stability of either is
difficult and costly to obtain.
The rate at which the clock pulses from the clock pulse generator
are provided can be varied. This permits the rate to be adjusted so
the selected number of clock pulses are completed within the scan
in one direction or just prior to the completion of the return
scan.
The oscillating mirror scanning arrangement produces a sinusoidal
scan of the field providing a rate of scan which is inherently
nonlinear. This invention provides circuitry to correct for the
varying rate of scan when a sinusoidal scan is used.
The signals obtained from the photomultiplier detector contain
considerable noise which varies as a scan is made across a
particle. This noise is due to such factors as changnes in the
light source used for scanning, the inherent noise of the
photomultiplier, variations in the opacity of the particle being
scanned, as well as variations in the opacity of the field holder.
This noise can vary during a scan across a particle and also from
one scan to the next and can give rise to erratic triggering of the
threshold circuits used for establishing the minimum intensity and
minimum size required for detection of a scanned particle. The
invention presented herein prevents erratic operation due to such
noise by providing a feedback signal to the minimum intensity and
size threshold circuits once the photomulitplier output signal
satisfies the minimum intensity and minimum size thresholds. Once
the initial intensity and size requirements for a particle have
been met, information obtained in the prior scan of an object is
combined with the current scan and applied to the feedback circuit.
Information from a prior scan provides correction for the variation
in the signal from scan to scan and is provided by applying the
shift register circuit output to the feedback circuit with the
shift register circuit advanced one clock pulse for each scanning
cycle. Advancing the shift register causes the shift register
circuit to provide a signal to the feedback circuit earlier in a
scan that it functioned in the preceding similar scan. The shift
register circuit is then more likely to have an input signal
applied to it for each intercepting scan in a given direction
following the first particle indicating signal produced by a scan
of a particle made in such direction so that the necessary particle
indicating signals from the shift register circuit are provided to
prevent the production of more than one count signal for a given
particle.
The invention also provides circuitry to enable the operator of the
apparatus to easily adjust the intensity threshold correctly
without the use of a television type display or physical count of
the particles. Since the scanning arrangement utilized in this
invention permits the field holder to be physically moved, the
operator can position the field so the oscillating mirror will be
scanning a representative portion of the field. A meter reading
provides a visual measure of the number of interceptions producing
a particle indicating signal during scan of the field in the
selected position as the intensity threshold adjustment is varied
to facilitate making the adjustment correctly.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the invention, reference
should be made to the accompanying drawings, wherein like parts in
each of the several figures are identified by the same reference
characters, and wherein
FIG. 1 is a block diagram of the particle detection apparatus
embodying the invention;
FIG. 2 is a representation of the raster type of sinusoidal scan
used in connection with apparatus of FIG. 1;
FIG. 3 consists of a number of signal patterns for use in
describing the operation of the apparatus of FIG. 1; and
FIG. 3A consists of a number of signal patterns for use in
describing the operation of the apparatus of FIG. 1 when modified
slightly;
FIGS. 4, 5 and 6 are exemplary circuits for use in an apparatus as
shown in FIG. 1.
DETAILED DESCRIPTION
The particle detection apparatus of FIG. 1 includes a scanning
portion 10 which optically scans a field 12 to detect particles
that are at least equal to a predetermined size and produces a
particle indicating signal when such a particle is scanned. The
particle indicating signals are applied to a memory provided by a
shift register circuit 35 and to signal coincidence circuitry 48
which is also connected to the ouput of the shift register circuit.
A clock pulse generator 11 connected to the shift register circuit
provides clock pulses for determining when the shift register
circuit will respond to particle indicating signals applied via
conductor 41 to the input of the shift register circuit.
The scanning portion 10 includes the optical scanner 14 and a light
responsive device 15, which may be a photomultiplier tube, for
providing signals when particles in the field 12 are intercepted by
a scan plus signal processing circuitry which includes amplifier
16, minimum intensity circuit 17, minimum size circuit 18, pulse
stretcher circuit 19 and feedback circuit 20 for providing particle
indicating signals when the signals from photomultiplier 15 satisfy
operator selected intensity and size thresholds. The optical
scanner 14 includes an oscillating mirror assembly 21, a mirror
control circuit 22, a light source 23, a Fresnel or condensing lens
24, focusing lens 25, pin-hole 26, and motor 27. The mirror
assembly 21 includes a mirror 93. While the optical path shown in
FIG. 1 for scanner 14 uses light transmitted by the field 12, it is
apparent to those skilled in the art that light reflected from the
field 12 could be used.
The mirror control circuit 22 is electrically connected to the
oscillating mirror assembly 21 via conductors 28 and 29. Conductor
28 provides a signal from the mirror assembly 21 to the mirror
control circuit 22 indicative of the mirror's position while
conductor 29 serves to apply a drive signal to the mirror assembly
21 from the mirror control circuit 22. The mirror control circuit
22 also provides a synchronizing pulse to the clock pulse generator
11 at the beginning of each cycle of the mirror 93 via the
conducting path 30.
The light from light source 23 passes through the condensing or
Fresnel lens 24 and the field 12 containing the particles to be
measured to the mirror 93 where it is reflected for passage to the
focusing lens 25, thence via the pin-hole 26 to the photomultiplier
15.
At the start of a scan of the field 12, the motor 27 drives the
field 12 to the right as viewed in FIG. 1, while the mirror 93
oscillates to produce a scanning locus that is transverse to the
movement of the field 12 causing the field 12 to be scanned by a
sinusoidal scan of the type illustrated in FIG. 2. The scanning to
the right and left, as shown in FIG. 2, is due to the movement of
mirror 93, while the movement of the field 12 provides vertical
coverage of the field. The scan lines are much closer together than
is shown in the drawing for FIG. 2 which is not drawn to scale. One
scan cycle includes a scan from one side to the other and return.
The degree of resolution for the vertical portion of the scan, as
shown in FIG. 2, is determined by the speed with which the field 12
is moved, while resolution provided by the side to side scanning,
is a function of the number of pulses provided by the clock pulse
generator 11 and the portion of the scan cycle during which the
pulses are provided. A particle 1 is shown in FIG. 2 to illustrate
how a particle may be intercepted by more than one scan.
The clock pulse generator 11 provides a selected number of clock
pulses following the receipt of each synchronizing pulse from the
mirror control circuit 22. The clock pulse generator 11 may include
an oscillator 31, a divider 32 and a flip-flop circuit 33. The
output of the oscillator 31 is applied to the divider 32 which,
after receiving the selected number of pulses to be provided by the
pulse generator 11, supplies a set signal to the flip-flop 33
causing the flip-flop circuit to provide a signal to the oscillator
31 via conductor 34 which is effective to inhibit further operation
of the oscillator. The synchronizing pulse from the mirror control
circuit 22 for the clock pulse generator 11 is applied via
conductor 30 to the flip-flop 33 and serves to reset it to remove
the inhibiting signal supplied to osciallator 31, causing it to
again provide the selected number of clock pulses.
The selected number of clock pulses provided by the generator 11 is
equal to the number of clock pulses required by the shift register
circuit 35 to have its response to a given input signal appear at
its output. The shift register circuit receives clock pulses from
the clock pulse generator 11 via conductor 36 NAND circuit 37 and
conductor 38. These clock pulses are also applied to a pulse
stretcher circuit 19 from conductor 38. The signal pattern 39 in
FIG. 3 represents the clock pulses as they appear at the output of
the NAND circuit 37. The clock pulses supplied to the divider 32
are also supplied to the pulse stretcher circuit 19 via conductor
13 and are represented by the signal pattern 40 in FIG. 3.
Adjustment of the frequency of the scanning cycles and/or the rate
at which the clock pulses are produced makes it possible to
establish the point in a scan cycle when the last of the selected
number of clock pulses for a scan cycle is produced. In the
apparatus of FIG. 1 the pulse rate or frequency of the pulse
generator 11 is adjustable and is set so the selected pulse number
of clock pulses, which begin with the synchronizing pulse provided
at the beginning of each cycle of the mirror 93, are completed
immediately prior to the completion of the first half of scan
cycle. That portion of the scan cycle during which clock pulses are
provided will hereinafter be referred to as an operative scan.
As the plurality of particles dispersed over the field 12 is
scanned, the output of photomultiplier 15 changes with the
variations in light intensity at the photomultiplier 15 due to
interception of the particles by the scanning process. The output
of the photomultiplier is applied to the amplifier 16 to provide a
signal level that can be processed by circuitry 17-20.
Signals at the output of amplifier 16 due to the interception of a
particle must satisfy an intensity threshold, i.e., the amplitude
must be at least equal to the minimum level determined by the
minimum intensity circuit 17. The minimum intensity setting is
controlled by the operator of the apparatus. If the signal
satisfies the established intensity threshold, it is then applied
to the minimum size circuit 18 to determine whether it is of a
duration sufficient to satisfy the minimum size threshold
established by that circuit. The minimum size setting is also
controlled by the operator. If the minimum size threshold is
satisfied, the circuit 18 provides a signal which indicates that
all threshold requirements have been satisfied. Such a signal will
hereinafter be referred to as a particle indicating signal. The
particle indicating signal has a duration indicative of the extent
to which the intercepting scan of the particle continues beyond the
intercept length required to satisfy the minimum size
threshold.
It is apparent that a particle indicating signal can have a very
short duration when produced in response to a scan of a particle
which only continues for a very short time beyond the duration
needed to satisfy the size threshold as set by the circuit 18.
Before the particle indicating signals are used further for
counting particles they are applied to the pulse stretcher circuit
19 which serves to extend the duration of each particle indicating
signal received from the minimum size circuit 18 during an
operative scan. The stretched particle indicating signal appears at
the output conductor 41 which connects with the input of shift
register circuit 35. The shift register circuit 35 is operated by a
signal applied to its input if such signal is present when a
positive-going clock pulse is received by the shift register
circuit. A particle indicating signal must be present during at
least one of the clock pulses in order to have the shift register
circuit 35 respond to the pulse indicating signal. The pulse
stretching action of circuit 19 is therefore quite important since
it will assure the signal coincidence needed for proper operation
of the shift register circut 35 in response to an input signal from
circuit 19.
The pulse stretching operation of circuit 19 can be best understood
by considering the signal patterns shown in FIG. 3. The signal
patterns are representative of the operation of a counting
apparatus according to this invention using the pulse stretcher
circuit 19 shown in FIG. 4 which includes a signal inverter 65 and
two D-type flip-flop circuits 66 and 67. The flip-flop circuits can
be those provided by a commercially available dual unit identified
as an SN747N integrated circuit.The clear and D inputs for
flip-flop 66 are connected to the output of the inverter 65 which
has its input 68 connected to the output of the minimum size
circuit 18. The clear and D inputs for flip-flop 67 connect with
the Q output of flip-flop 66. The preset terminals for each
flip-flop connect with a positive 2.5 volt source (not shown). The
flip-flop circuits 66 and 67 respond to low level clear and preset
inputs and to positive going clock pulses. Clock pulses are appled
to flip-flops 66 and 67 via conductors 38 and 13, respectively.
Referring to FIG. 3, the signal pattern 42 is representative of an
output signal for the photomultiplier 15. The two positive portions
indicate the interception by a scan of two particles. The signal
pattern 42 causes the digital type signal pattern 43 to be
presented at the output of the minimum size circuit 18. The clock
pulses appearing on conductor 13 are represented by the signal
pattern 40, while the signal pattern 39 represents the clock pulses
which appear on conductor 38. The response at the Q output of
flip-flop 66 to the signal pattern 43 is represented by the signal
pattern 44. The response at the Q output of flip-flop 67 to the
signal pattern 43 is represented by the signal pattern 45. The
effective data input shifted by shift register circuit 35 in
response to the signal pattern 45 from pulse stretcher circuit 19
is indicated by the signal pattern 46. The inverse of signal 45 is
produced at the Q output of the flip-flop 67 to which conductor 47
is connected and is indicated by the signal pattern 45.
With the pulse stretcher circuit 19 described, a high signal at the
input of inverter 65 is presented as a low level to the clear input
of flip-flop 66 which is immediately transferred as a low signal at
Q of flip-flop 66 with such signal remaining until the input signal
to inverter 65 becomes low and a positive-going clock pulse
transition is received from conductor 38. Thus, referring to the
first positive pulse in the signal pattern 43, which is applied to
the input of the inverter 65, the signal 44 at Q of flip-flop 66
becomes low and remains so until the input to inverter 65 per
signal pattern 43 becomes low and a positive going clock pulse
transition is received by flip-flop 66 via conductor 38 per signal
pattern 39. The low signal at Q of flip-flop 66 causes the Q output
of flip-flop 67 (signal pattern 45) to be low and remain so until
the signal at Q of flip-flop 66 is high and a positive going clock
pulse transition per signal pattern 40 is applied to the flip-flop
77 from the clock pulse generator via conductor 13. The first
positive going pulse per signal pattern 43 is thus stretched or
increased in duration as shown by the signal pattern 45 and acts as
a data input to the shift register circuit 35 since it is present
when the second clock pulse per signal pattern 39 is presented to
the shift register circuit 35. As can be seen, this coincidence for
operation of the shift register circuit 35 would not have occurred
had the signal from the minimum size circuit 18 per signal pattern
43 not been increased in duration. The same is true for the second
pulse in the signal pattern 43.
It should be noted that the degree to which a particle indicating
signal is increased in duration varies since the incnrease is
dependent on its duration and the time of occurrence in relation to
the clock pulses. A circuit providing a fixed delay is not as
desirable since erroneous counts will be produced under some
circumstances. The circuit 19 described does have a limit as to the
delay that can be introduced. The greatest delay possible will
provide an output signal from the pulse stretcher circuit 19 having
a duration of one and one-half clock pulse cycles.
A particle in a field being scanned may be scanned more than once
giving rise to more than one particle indicating signal from the
pulse stretcher circuit 19 for a given particle. It is desirable
that only one such signal be used to count the particle. The pulse
stretcher 19 on the first scann scan a particle resulting in a
particle indicating signal provides information indicating the
particle satisfies the threshold requirements. At any point in an
operative scan, the shift register circuit 35 provides an output
signal which is indicative of the input signal it received from the
pulse stretcher circuit 19 during the corresponding portion of the
preceding operative scan. Accordingly, the output of the shift
register circuit 35 at the time the firs particle indicating signal
is produced for a given particle will indicate a particle
indicating signal was not produced for the given particle during
the preceding operative scan. The shift register circuit 35 during
the subsequent operative scan of the given particle will provide an
output signal indicating that a particle indicating signal was
produced by the preceding scan of the given particle. A signal at
the output of the shift register circuit 35 providing such
information will hereinafter be referred to as a shift register
circuit particle indicating signal.
Signal coincidence circuitry 48 provides the logic needed to use
the output from the pulse stretcher circuit 19 and the shift
register circuit 35 for determining whether a count signal should
be produced. The circuitry 48 includes a leading edge detector 49,
a trailing edge detector 50, a flip-flop circuit 51 and a NOR
circuit 52. The circuit details for circuitry 48 is shown in FIG.
6. A positive signal presented on conductor 47 will cause a count
signal to be presented at the output of NOR circuit 52 provided a
positive or high signal is not received at the reset input 54 of
flip-flop 51 prior to the termination of the positive signal
presented on conductor 47. Accordingly, a particle indicating
signal is received from pulse stretcher circuit 19 via conductor 47
and provides a count signal unless a particle indicating signal
from the output of the shift register circuit 35 is received by the
flip-flop 51 before the particle indicating signal from pulse
stretcher circuit 19 is terminated. The output of the shift
register circuit 35 is presented via the conducting path 53 to the
reset input 54 of the flip-flop 51, while the output from the pulse
stretcher circuit 19 is applied via conductor 47 to the input for
the leading edge detector 39 and the trailing edge detector 50. The
output from the leading edge detector 49 is connected to the set
input 55 of the flip-flop 51. The output for the flip-flop 51 is
applied to input 56 of the NOR circuit 52 with another input 57
being supplied from the output of the trailing edge detector.
A particle indicating signal provided by the pulse stretcher 19 to
the leading edge detector 49 and trailing edge detector 50 is shown
by the signal pattern 45. In response thereto, the leading edge
detector 49, as shown by signal pattern 5 of FIG. 3, provides a
sharp positive going pulse at its output corresponding to the
leading edge of the signal which causes the flip-flop circuit 51 to
be set to present a low signal to the input 56 of the NOR circuit
52. If the preceding operative scan did not produce a particle
indicating signal for the particle, the output of the shift
register circuit 35 for the current scan of the particle is low
causing the flip-flop circuit 51 to remain set. If the preceding
operative scan of the particle produced a particle indicating
signal for the particle, the output of the shift register circuit
for the current scan of the particle is a particle indicating
signal which is high causing the flip-flop to be reset to present a
high signal to the input 56 of the NOR circuit 52. The trailing
edge detector 50 produces a negative going pulse, as shown by
signal pattern 6 of FIG. 3, corresponding to the trailing edge of a
particle indicating signal 45 from the pulse stretcher circuit 19.
Two low inputs will thus be present at the NOR circuit 52 when the
flip-flop 51 has not been reset by the output of the shift register
circuit 35 after the flip-flop 51 has been set by the leading edge
detector 49 causing a high signal to appear at the output of the
NOR circuit which is used to increase the count by one. A low input
to the NOR circuit 52 from the trailing edge detector 50 plus a
high input from the flip-flop 51 due to resetting of the flip-flop
51 by a high or particle indicating signal received from the shift
register circuit 35 causes a low signal to be produced at the
output of the NOR circuit 52 which will not effect a count. In
summary, if a high or particle indicating signal from shift
register circuit 35 needed to reset flip-flop 51 is applied after
the flip-flop 51 has been set by the leading edge detector 49 and
before the trailing edge detector 50 provides a negative going
pulse to the NOR circuit 52, the NOR circuit 52 will not provide a
count signal, but if a high or particle indicating signal from
shift register 35 needed to reset flip-flop 51 is not applied after
the flip-flop 51 has been set by the leading edge detector and
prior to the occurrence of a negative going pulse from the trailing
edge detector 50, the NOR circuit 52 will provide a count signal.
Accordingly, since a particle indicating signal will be presented
to the flip-flop circuit 51 from the shift register circuit 35
prior to the end of the particle indicating signal obtained from
circuit 19 for every operable scan of a particle subsequent to the
first particle indicating signal scan, only one count signal will
be produced for each particle giving rise to a particle indicating
signal.
The ouput of NOR circuit 52 is applied to one input of a NAND
circuit 58 which has its second input connected to a motor and
count control circuit 59. The output of the NAND circuit 58 is
applied to a count and display circuit 60. A high signal must be
supplied to the NAND circuit 58 from the motor and count control
circuit 59 when a count signal is supplied to the NAND circuit 58
from NOR circuit 52 to cause the NAND circuit 58 to provide a low
signal to the count and display 60 to cause the count to be
increased by one. The count and display 60 may be a readout tube
arrangement which is well known to those skilled in the art. The
motor and count control circuit also connects with the motor 27 to
initiate movement of the field holder 12 by motor 27 for a scan.
The motor 27 operation and application of the necessary signal to
the NAND circuit 58 to permit passage of a count signal are
correlated so counting can begin as soon as the field holder 12 has
begun its movement for a scan.
As has been indicated, operation of the signal coincidence
circuitry 48 is such that a positive signal presented on conductor
47 will cause a count signal to be presented at the output of NOR
circuit 52 provided a positive or high signal is not received at
the reset input 54 of flip-flop 51 prior to the termination of the
positive signal presented on conductor 47. Using the connections to
the circuitry 48 as indicated in FIG. 1 and FIG. 6, it was shown
that only the first particle indicating signal for a scanned
particle presented on conductor 47 from the pulse stretcher circuit
19 would cause a count signal to be produced with all subsequent
particle indicating signals for a particle obtained from the pulse
stretching circuit being ineffective to produce a count signal due
to the positive reset signals presented by the shift register
circuit 35 during all operable scans of a particle subsequent to
the first operable scan.
It is possible to modify the circuitry of FIG. 1 slightly to
provide alternate operable arrangement. The output on conductor 47
from pulse stretcher circuit 19 can be connected to the reset input
54 of flip-flop 51 while the output of the shift register circuit
35 is changed to connect to the leading edge detector 49 and the
trailing edge detector 50. This will also provide a circuit which
will operate so that only one count signal will be produced for
each particle scanned that is large enough to produce a particle
indicating signal. Referring to FIG. 3A, the signal pattern 4 is
representative of the output from the shift register circuit 35 for
an operative scan subsequent to the operative scan resulting in the
initial particle indicating signal per 43 of FIG. 3. This signal
applied to circuits 49 and 50 causes signal patterns 5a and 6a to
be produced at the output of circuits 49 and 50 respectively. The
signal pattern 45 of FIG. 3A is the signal pattern obtained from
the pulse stretcher 19 which is now considered being applied to the
reset input of flip-flop 51. With this arrangement, the pulse
stretcher circuit 19 for a given particle scanned will provide a
reset signal to the flip-flop 51 for each particle indicating
signal received from the shift register circuit 35 except the last
such signal received which will be due to the last particle
indicating signal scan produced by a scan of the particle. The last
particle indicating signal from the shift register circuit 35 for a
given particle will be provided when the current scan is not giving
rise to a particle indicating signal at the conductor 47 of the
pulse stretcher circuit 19 causing such last particle indicating
signal from circuit 35 to give rise to a count signal from NOR
circuit 52 of the signal coincidence circuit 48.
No consideration has been given feedback circuit 20 which forms a
part of the circuitry for processing the signals received from the
photomultiplier 15 and it is not needed if only well-defined
objects were to be counted. However, cases do arise where the light
intensity at the photomultiplier 15 as an object is scanned varies
due to the object itself plus the electrical noise from the
photomultiplier, variations in the optical characteristics of the
field holder 12 and variations in the intensity of the light source
23, causing erratic triggering of the minimum intensity and size
circuits 17, 18. The feedback circuit 20 eliminates such erratic
triggering by applying the output from the minimum size circuit 18
to the minimum intensity circuit 17 and minimum size circuit 18 to
effect a reduction in the threshold requirements so that once a
signal is developed at the output of the minimum size circuit 18 it
will continue for the duration of the scan of the signal producing
particle.
The signal from the output of the minimum size circuit 18 is
applied to the feedback circuit 20 via a NOR circuit 61 since the
output of the shift register circuit 35 is also applied to the
feedback circuit 20. By using the NOR circuit 61, the prsence of a
feedback signal from either circuit 18 or 35 will then effect the
desired reduction in the threshold requirements. Inputs 62 and 63
of the NOR circuit 61 connect with the output of a minimum size
circuit 18 and shift register circuit 35, respectively.
Since the clock pulse generator 11 provides the number of clock
pulses to the shift register circuit 35 during each operative scan
to complete one cycle of operation, the effective data input
shifted by the shift register circuit 35, such as shown by signal
pattern 46, will appear at the output of the shift register circuit
35 at the same point in the next corresponding operative scan.
However, one clock pulse is supplied to the shift register circuit
35 for each scan cycle in addition to the clock pulses provided by
the clock pulse generator 11, causing the output of the shift
register circuit 35 to be advanced one clock pulse each scan cycle.
Signal pattern 4 of FIG. 3 therefor shows the output of the shift
register circuit 35 presented during the operative scan which
follows the operative scan which gave rise to the singal pattern 46
and as can be seen, is the same as signal pattern 46, but is
advanced one clock pulse. This provides the feedback circuit 20
with a signal from the shift register circuit 35 one clock pulse
earlier causing reduction of the threshold levels for the minimum
intensity circuit 17 and the minimum size circuit 18 by the
feedback circuit due to the output of the shift register circuit 35
to occur earlier during corresponding operative scans subsequent to
the first operative scan of a particle giving rise to a particle
indicating signal for the particle thus assuring that a particle
indicating signal will be provided for each corresponding operative
scan of the particle subsequent to the first particle indicating
operative scan. Having a particle indicating signal for each
corresponding operative scan of a particle subsequent to the first
particle indicating operative scan which will operate the shift
register circuit 35 is important if the shift register circuit is
to provide the necessary particle indicating signal at its output
for operation of the signal coincidence circuitry 48 to prevent
multiple counts of a single particle.
The advantage of advancing of the shift register circuit 35 output
one clock pulse can be appreciated by considering the signal
patterns of FIG. 3. If the next operative scan of a particle were
to repeat the signal 42 of FIG. 3, the output of the shift register
circuit 35, when advanced one clock pulse as shown per signal
pattern 4, indicates the particle indicating signal portion of the
shift register circuit 35 output (shaded portion) coincides with
the photomultiplier output per signal pattern 42 to improve the
desired signal coincidence needed to prevent a multiple count. The
additional clock pulse needed to advance the shift register 35 is
provided by using the synchronizing pulse provided by the mirror
control circuit 22 at the beginning of each scan cycle. It is
applied to the shift register 35 via the NAND circuit 37 which is
connected with the mirror control circuit 22 by the conductor
64.
Since the scan provided by the oscillating mirror 21 and movement
of the field 12 is sinusoidal in nature the rate of the scan will
vary. Compensation for this inherent nonlinearity in the rate of
scan is provided by applying a signal to the minimum size circuit
18 during each operational scan which is proportional to the
magnitude of the rate of scan. Such a signal may be obtained from
the mirror control circuit 22 since it controls the mirror 93 and
receives information from the mirror 21 assembly relative to the
position of mirror 93. The signal providing the compensation is
applied to the minimum size circuit via the conductor 69.
The output of the photomultiplier 15 is a function of the intensity
of the light from the background of the field being scanned and
from the objects being counted. Many times there is only a slight
difference between the two intensity levels making it essential the
intensity threshold adjustment for the minimum intensity circuit 17
be accurately made for an accurate count of particles of a
predetermined size range. This is made possible by that portion of
the circuitry of FIG. 1 which includes the amplifier 70, the
nonlinear transfer circuit 71 and the display device 72. The
amplifier 70 is connected to the output of the leading edge
detector 49. The amplifier has its output applied to the nonlinear
transfer circuit 71 which in turn drives the display device which
can be a simple d.c. ammeter. This arrangement provides for a
simple method to establish the optimum intensity threshold setting.
The operator selects a representative portion of the field 12 for
making the intensity threshold adjustment and moves the field 12
into position for scanning. During the scanning which is done only
by the mirror 93, the intensity threshold adjustment is moved from
one extreme end of its range to the other while the deflection
provided by the ammeter 72 is observed. The meter 72 will initially
have a low reading, then reach a maximum reading at some
intermediate range and then drop off to a low reading. The operator
need only manipulate the threshold adjustment as he observes the
meter 72 until he is satisfied that the setting is about mid-range
of the span providing the maximum meter reading. While the output
from the leading edge detector 49 has been used, it is apparent
that the output of the trailing edge detector 50, can be used to
provide the same information required to provide the desired input
for the display device 72. It is only necessary to invert the
output from the trailing edge detector 50 to use it with circuits
70-72.
The apparatus as shown in FIG. 1 uses an operative scan which
includes only the first scan of each scan cycle. The arrangement
per FIG. 1 can be easily modified so the operational scan includes
both scans of a scan cycle. This requires a reduction of the
frequency of oscillator 31 so the selected number of clock pulse
begin with each scan cycle and continue until just prior to the end
of a scan cycle. This, of course, means two count signals are
produced when a particle is intercepted by both scans of a scan
cycle. This requires the addition of a divide by two divider to the
arrangement of FIG. 1 so the proper number of count signals are
provided. Such a divider when used is connected between the output
of the NAND circuit 58 and the count and display 60.
The fact that the frequency of the oscillator 31 can be changed and
no change need be made in the shift register circuit 35 makes it
possible to use an oscillating mirror 21 that need not be
manufactured to any close tolerances as far as its mechanically
resonant frequency is concerned since any variation from unit to
unit is taken care of by the oscillator 31 frequency adjustment. In
addition, it can be appreciated that other scanning schemes having
a scanning frequency different from that provided by the
oscillating mirror 21 can be readily adapted for use with the
electronics provided for the apparatus of FIG. 1.
SPECIFIC COMPONENTS AND CIRCUITRY
Some of the apparatus and its operation has been described largely
in terms of the functions performed by the various elements and
combinations thereof as set forth in FIG. 1. Further details
regarding circuitry and components that can be used to facilitate
construction of an apparatus as disclosed in connection with FIG. 1
will be given.
FIG. 5 sets forth the details for circuits which can be used for
the clock pulse generator 11, mirror assembly 21, mirror control
circuit 22, minimum intensity circuit 17, minimum size circuit 18
and the feedback circuit 20.
The oscillator 31 for pulse generator 11 includes a free-running
multivibrator with provision made to connect a signal from
flip-flop 33 for inhibiting operation of the multivibrator. A pulse
forming portion is also included for providing the narrow clock
pulses required for operation of the pulse stretcher circuit 19 and
the shift register 35. Adjustment of its frequency of operation is
made possible by the potentiometer 74. The inhibiting signal from
flip-flop 33 is applied to the multivibrator via an inverter
circuit 76. The collector of transistor 86 is connected to an
inverter 84 which in turn connects with the divider 32 and via
conductor 13 to the pulse stretcher 19. The output of the inverter
84 is also applied to the pulse forming portion of the generator 11
which is a differentiating circuit that includes the capacitor 87
and resistor 88. The diode 89 connected in parallel with resistor
88 is used to provide positive voltage protection for the NAND
circuit 37 to which the output from differentiating circuit of the
oscillator 31 is applied.
A particle counter which uses 2.sup.10 or 1024 clock pulses for an
operative scan provides adequate resolution. The number of clock
purles per operative scan establishes the requirements for divider
32 and the number of stages for shift register circuit 35. With
1024 clock pulses used for an operative scan, the divider 32 is
capable of dividing by 1024 and the shift register circuit 35
requires 1024 clock pulses for one complete cycle of operation.
A divider 32 capable of dividing by 1024 may be formed by
connecting three hexadecimal counters 90-92, as shown in FIG. 5.
The counters may be 7493N type integrated circuits. The actual
terminal designations for the counters are shown. The first
flip-flop circuit of counter 90 is not included as a part of the
divider 32 nor is the last flip-flop of counter 92. The last
flip-flop of counter 92 can be used in the flip-flop circuit 33
which also includes an inverter 121 for receiving a reset signal.
Upon receipt of the 1024th pulse from oscillator 31, all of the
flip-flops for the divider 32 will be presenting a 0 at their
outputs. As the final flip-flop of the divider 32 presents a 0, the
flip-flop circuit 33 will present a 1 at its output which via
conductor 34 is applied to the oscillator 31 to inhibit its
operation. The inhibit signal is removed when the inverter 121 of
flip-flop circuit 33 receives a reset signal from the mirror
control circuit 22 via conductor 30.
In the event the operative scan includes the entire scan cycle, the
first flip-flop of counter 90 can provide the divide by two circuit
which, as indicated earlier, is then required to be connected
between the NAND circuit 58 and the count and display 60.
An oscillating mirror capable of oscillating at a rate of 200
cycles per second may be used. A Bulova American Time Products L50
scanner may be used as the oscillating mirror assembly 21. The L50
scanner includes the mirror 93 supported by a taut band at its
center with permanent magnets 94 and 95 mounted at opposite ends of
the mirror. The magnets 94 and 95 are magnetically coupled to coils
96 and 97, respectively, and are included as a part of the L50
scanner. A capacitor 98 is connected in parallel with coil 97 to
reduce high frequency noise pick-up. Coil 97 is used for sensing
the position of the mirror 93 with respect to magnet 95 while coil
96 serves as drive coil and has a capacitor 9 connected in parallel
with it to suppress noise generation. The drive and sensing coils
96, 97 are connected as a part of the mirror control circuit 22
which includes an oscillator-amplifier utilizing two operational
amplifiers 99 and 100. Amplifier 99 receives a sinusoidal input
from the sensing coil 97 via conductor 28 which is amplified and
applied to the amplifier 100 connected to operate in the saturated
mode. The output from amplifier 100 is essentially a square wave
which is applied to the drive coil 96 via conductor 29. The
amplifier-oscillator serves to keep the oscillating mirror 21
oscillating at its mechanically resonant frequency which is
approximately 200 HZ. The amplitude of the oscillations is
determined by the setting of the potentiometer 112.
The mirror control circuit 22 also provides a signal for advancing
the shift register 35 one clock pulse and for resetting the
flip-flop 33 of the clock pulse generator 11. The circuitry to the
right of the amplifier 100 in FIG. 5 is provided for this purpose.
It sharpens the edges and then differentiates the output from
amplifier 100 to obtain the narrow pulse needed at the start of
each scan cycle to reset flip-flop 33 and advance the shift
register circuit 35. As was the case for the differentiating
circuit included with oscillator 31 circuitry, the diode 120
connected across the resistor 119 of the differentiating circuit
portion is used to provide positive voltage protection for the NAND
circuit 37 and, also inverter 121 of the flip-flop circuit 31.
Amplification of the output of the photomultiplier 15 can be
obtained using any of a number of suitable amplifiers for the
amplifier 16 which connects with the minimum intensity circuit 17.
A circuit suitable for use as a minimum intensity circuit 17 is
shown in Fig. 5 and includes means for adjusting the bias of an
operational amplifier 3 which establishes the intensity threshold.
The bias adjustment is obtained using the adjustable resistance
formed by the fixed resistor 122 and a potentiometer 123 connected
between a positive 5 volts and ground with the movable contact of
the potentiometer connected via a switch 124 to either input of the
amplifier 3. The switch 124 is provided since the particles being
counted can give rise to an increase in current at the
photomultiplier 15 or may cause a decrease in the output of the
photomultiplier 15. The movable contacts of switch 124 are
therefore positioned to the left or to the right dependent upon the
type of particle being counted. If the signal is in excess of the
bias setting, the minimum intensity threshold is satisfied by the
detected particle causing a negative going pulse to be presented at
the output of the amplifier 3. The duration of the pulse is
determined by the length of the interception of the particle by the
scan.
A circuit suitable for use as a minimum size circuit 18 is shown in
FIG. 5 and includes an integrating circuit portion and a level
detector circuit portion. The integrating circuit portion includes
the operational amplifier 134 and transistor 142 while the level
detector circuit portion includes the operational amplifier 147.
The operational amplifier 134 has its input coupled to the output
of the operational amplifier 99 of the mirror control circuit 22
and receives a sinusoidal signal when the mirror 93 is oscillating.
The output of amplifier 134 at any instant is therefore
proportional to the rate of scanning of mirror 21 and is negative
since amplifier 134 acts as an inverter. The output of the
amplifier 134 is coupled to the base of the transistor 142 to
control the operation of the transistor 142 to provide compensation
for the nonlinear rate of scan present when the disclosed
sinusoidal scanning arrangement is used. The output of the minimum
intensity circuit 17 is also connected to the base of transistor
142 and presents a negative signal indicative of the sensing of an
object. During the half cycle corresponding to the operative scan,
the transistor 142 circuitry integrates any signal received from
the minimum intensity circuit 17 with the resulting signal being
proportional to the duration and magnitude of the signal from the
minimum intensity circuit 17 and the rate or scanning by the mirror
21. If the signal developed by the integrating process has an
amplitude sufficient to overcome the bias setting of the
operational amplifier 147 determined by the potentiometer 153 which
establishes the size threshold, the operational amplifier 147 will
provide an output signal having a duration corresponding to the
time the integrated signal exceeds the signal level required by the
bias setting. The output of the amplifier 147 is coupled to the
pulse stretcher circuit 19 and to one input of the NOR circuit 61
connecting with the feedback circuit 20.
The other half cycle of the sinusoidal signal from the motor
control circuit 22 presented to amplifier 134 does not influence
the operation of the amplifier 134 since it then is under the
control of the positive voltage coupled to the input of the
operational amplifier via the resistor 131 connected in series with
resistor 136 between a positive 15 volts and the base of transistor
142. The positive voltage then causes the output of the transistor
142 to stay low irrespective of a signal that may be received by
the minimum circuit 17 from the minimum intensity circuit 18.
In the event the operative scan includes both scans in the scan
cycle, the minimum size circuit 18 is modified slightly to provide
the rate of scan compensating signal for the entire scan cycle.
This requires the removal of the resistor 131 which connects with
the positive 15 volts and replacing it with a diode having its
cathode connected to the output of operational amplifier 99 and its
anode connected to the anode of diode 135. Such a diode may be of
the same type as is used for diode 135.
A circuit suitable for use as the feedback circuit 20 is set forth
at the bottom of FIG. 5 and includes an inverter 154 for amplifying
and inverting the output from NOR circuit 61. Transistor 159
conducts in response to the output of the NOR circuit 61 when a
feedback signal is received by the NOR circuit from the shift
register circuit 35 or the minimum size circuit 18 causing the
threshold requirements for the minimum intensity and size circuits
17 and 18 to be reduced.
A suitable shift register circuit 35 is shown in FIG. 6 together
with details of circuits suitable for use in forming the signal
coincidence circuitry 48. The shift register circuit 35 includes a
1024 bit static shift register 163 available under the designation
2533V with a resistor 164 connected between the clock input for the
shift register 163 and a positive 5 volt source (not shown). The
output of the shift register 163 is connected to an inverter 165
the output of which provides the output for the shift register
circuit 35.
The leading edge circuit 49 and the trailing edge circuit 50 are
identical except that the leading edge circuit includes an inverter
166 connected to the differentiating portion including the
capacitor 167 and resistor 168 and also has an inverter 170 for
coupling the signal to the flip-flop circuit 51. A diode 169 is
connected across the resistor 168 to provide positive voltage
protection for the inverter circuit 170. The trailing edge circuit
50 has the differentiating circuit including capacitor 171,
resistor 172 and the positive voltage protecting diode 173. With
this arrangement, the positive going leading edge of a particle
indicating signal received from the pulse stretcher 19 causes a
positive going pulse to be produced by the leading edge circuit 49
to set the flip-flop 51 while the negative going trailing edge of
the signal from pulse stretcher 19 causes a negative going pulse to
be produced by the trailing edge circuit 50 which is applied to the
input 57 of the NOR circuit 52.
The flip-flop circuit 51 may be formed using two NOR circuits 174
and 175. The set input 55 for the circuit 51 is the input of NOR
circuit 174 connected to the leading edge circuit 49. The other
input of NOR circuit 174 is connected to the output of NOR circuit
175. The output of NOR circuit 174 connects to one input of NOR
circuit 175 and to input 56 for NOR circuit 52. The other input for
NOR circuit 175 is the reset input 54 for flip-flop 51 and is
connected to the output of the shift register circuit 35.
The circuitry which may be used for the amplifier 70 and the
non-linear transfer circuit 71 to drive a display device 72, such
as a d.c. ammeter, in accordance with the positive going pulses at
the output of the leading edge circuit is also shown in FIG. 6. The
transistor 177 provides the necessary amplification for amplifier
70 while the capacitor 179 and resistors 178, 180 provide the
transfer circuit 71 connected to drive the meter 72.
The specific circuits shown in FIGS. 4, 5 and 6 are purely
exemplary and other equivalent circuits may be utilized. To
complete the disclosure for the circuits of FIGS. 4, 5 and 6, the
various circuit components which have not been discussed previously
with respect to value or type, are listed below with the nominal
values or type listed for each component. It should be noted also
that the d.c. voltages required for operation of some of the
components have not been indicated. A positive 5 volts is required
for operation of the NAND, NOR inverter, flip-flop and counter
circuits used. The operational amplifiers connect with a positive
15 volts and a negative 12 volts.
______________________________________ COMPONENT VALUE OR TYPE
______________________________________ All Inverters SN7404N All
NAND Circuits SN7400N All NOR Circuits SN7402N All Transistors
2N2369 Capacitors 140 .005 uf 98, 109 .015 uf 9 .025 uf 179 10 uf
82, 83 100 pf 8, 87, 167, 171 750 pf Diodes All except 162 1N914
162 1N276 Meter 72 0-1 MA, DC Operational Amplifiers 99 SN741P 100,
134 1/2 SN72558P or SN72741 121 709 3, 147 SN72709P Photomultiplier
15 931A Potentiometers 104 200 ohm 74, 112 500 ohm 123, 153 1K ohm
101 10K ohm Resistors 139 33 ohm 178 100 ohm 103 390 ohm 77, 81 470
ohm 75 560 ohm 7 820 ohm 107, 113, 125, 145, 149, 155 1K ohm 78,
106, 111, 156, 176, 181 1.5K ohm 88, 117, 119, 148, 152 164,168,172
2.2K ohm 114, 122, 130, 141, 180 3.3K ohm 144 4.7K ohm 132, 133
4.99K ohm 127 5.6K ohm 105, 131, 157, 158 10K ohm 79, 80, 108, 136
15K ohm 143 33K ohm 102 47K ohm 146 120K ohm 110, 126 1 Meg ohm
______________________________________
* * * * *