U.S. patent number 3,768,084 [Application Number 05/271,753] was granted by the patent office on 1973-10-23 for particle counter having a clog and bubble alarm.
This patent grant is currently assigned to Becton, Dickinson and Company. Invention is credited to John L. Haynes.
United States Patent |
3,768,084 |
Haynes |
October 23, 1973 |
PARTICLE COUNTER HAVING A CLOG AND BUBBLE ALARM
Abstract
A fluid containing disbursed particles having a conductivity
substantially different than the fluid is pumped through an
aperture. A pair of electrodes are mounted so that one electrode is
on each side of said aperture and an rf signal is imposed upon the
electrodes to develop a voltage across the fluid passing through
the aperture. The rf signal is modulated by the conductivity of the
fluid instantaneously passing through the aperture so that when a
high resistance particle passes through the aperture, the rf signal
intensity increases in relationship to the rf signal intensity when
fluid is passing through the aperture. The rf signal is then
detected, filtered and amplified to provide pulses corresponding to
the particles passing through the aperture. Means are provided for
counting the pulses and for providing a readout indicating the
number of particles contained in a unit volume of the fluid. A clog
alarm driver circuit is connected to receive the filtered rf signal
and in response to a constant high level filtered signal provides
an output to an alarm for indicating a clogged aperture. The
amplified signal is directed to an amplifier clipper which further
amplifies the signal and establishes a base line at 8 volts DC with
pulses having an amplitude of approximately 4 to 6 volts. The
presence of bubbles at the aperture causes an erratic signal which
appears as base line noise and includes excursions below the 8 volt
DC base line output. These excursions intermittently turn on a
transistor which provides an output signal to a bubble alarm driver
which in response thereto provides an output to the
previously-mentioned alarm. A continuous alarm indicates a clogged
aperture while an intermittent alarm indicates the formation of
bubbles at the aperture.
Inventors: |
Haynes; John L. (Redwood City,
CA) |
Assignee: |
Becton, Dickinson and Company
(East Rutherford, NJ)
|
Family
ID: |
23036925 |
Appl.
No.: |
05/271,753 |
Filed: |
July 14, 1972 |
Current U.S.
Class: |
377/12;
340/608 |
Current CPC
Class: |
G01N
15/1227 (20130101); A61M 5/365 (20130101) |
Current International
Class: |
A61B
5/145 (20060101); A61M 5/36 (20060101); G01N
15/10 (20060101); G01N 15/12 (20060101); G08b
019/00 (); G06m 011/00 (); G01n 027/00 () |
Field of
Search: |
;340/243,239 ;235/92PC
;324/71CP ;317/DIG.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Myer; Daniel
Claims
What is claimed is:
1. An instrument for counting particles suspended in a fluid
medium, wherein the fluid medium and the particles have different
conductivities, comprising:
an aperture;
means for passing the fluid through the aperture;
means for applying an electrical signal across the aperture;
detecting means for detecting changes in the electrical signal
level across the aperture and for providing an output having pulses
corresponding to the changes in the electrical signal which result
from a change in impedance across the aperture as particles pass
through the aperture;
means for counting the pulses from the detecting means that exceed
a predetermined level and for providing an indication corresponding
to the number of particles per unit volume of the fluid;
clog detecting means responsive to the output from the detecting
means for sensing when the detecting means provides a constant
output exceeding a predetermined level resulting from a clogged
aperture and for providing a steady state signal output in response
thereto;
bubble detecting means responsive to the output from the detecting
means for detecting erratic and rapidly changing pulses which
result from the formation of bubbles adjacent the aperture and for
providing an intermittent signal output in response thereto;
and
indicator means, responsive to the signal outputs from the clog and
bubble detecting means, for providing a con-stant indication when a
clogged aperture exists and for providing an intermittent
indication when bubbles are formed adjacent the aperture.
2. An instrument as described in claim 1, wherein the clog
detecting means comprises a driver circuit biased to provide a
signal output when the output of the detecting means exceeds a
predetermined level.
3. An instrument as described in claim 1, wherein the bubble
detecting means comprises:
an amplifier clipper circuit for providing an output signal
corresponding to the output of the detecting means but biased at a
DC level; and
means for detecting when the amplifier clipper circuit output
signal drops below the DC bias level as a result of errotic and
rapidly changing pulses and for providing the intermittent signal
output in response thereto.
4. An instrument as described in claim 3, wherein the amplifier
clipper circuit comprises:
an operational amplifier having a first input for receiving the
output from the detecting means;
a biasing circuit connected to the first input for establishing a
DC bias level; and
a feedback loop connecting the amplifier output to a second input,
so that the amplifier provides an output signal biased at a DC
level.
5. An instrument as described in claim 4, wherein the means for
detecting when the output signal drops below the DC bias level
includes a transistor having the base to emitter junction connected
between the output and the second input of the operational
amplifier so that the transistor is turned on when the output
signal drops below the DC bias level.
6. In a particle counting apparatus of the type, wherein a fluid
medium containing particles having a conductivity different from
the fluid is passed through an aperture and electrodes positioned
at each side of the aperture are energized to develop a signal
corresponding to the impedance across the aperture so that the
particles cause signal changes as they pass through the aperture
and the changes are detected and counted to provide a readout
corresponding to the number of particles per unit volume of the
fluid medium, the improvement comprising:
clog detecting means for detecting a steady state electrical signal
across the electrodes that exceeds a predetermined level and for
providing a constant output in response thereto;
bubble detecting means for detecting erratic signal changes across
the electrodes and for providing an intermittent output in response
thereto; and
indicator means connected to the last two mentioned means and
responsive to the outputs therefrom for providing a constant
indication in response to the output of the first mentioned means
and an intermittent indication in response to the output of the
second mentioned means so that the constant indication is provided
when an aperture clog exists and an intermittent indication is
provided when bubbles are formed adjacent the aperture.
7. An instrument for counting the number of particles per unit
volume suspended in a fluid medium, said fluid medium having a
conductivity different than the particles, comprising:
an aperture;
means for passing the fluid through the aperture;
means for applying an electronic signal across the aperture;
detecting means for detecting changes in the electronic signal
level across the aperture and for forming pulses corresponding to
the changes which result from an increase in impedance across the
aperture as particles pass through the aperture;
means for counting the pulses that exceed a predetermined level and
for providing an indication corresponding to the number of
particles per unit volume of the fluid;
a clog alarm driver responsive to the output of the detecting means
for providing a steady state output when the aperture is
clogged;
a bubble detector and alarm driver responsive to the pulses from
the detecting means for providing an intermittent output when
bubbles are formed adjacent the aperture; and
an alarm indicator connected to the output of the clog alarm driver
and bubble detector and alarm driver and responsive to the signals
therefrom for providing a constant indication when the aperture is
clogged and an intermittent indication when bubbles are formed
adjacent the aperture.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to particle counters for counting
particles suspended in a fluid medium and more particularly to a
counter having an alarm for indicating the existence of an aperture
clog or the formation of bubbles adjacent the aperture.
2. Description of the Prior Art
The prior art in the field of particle counting may be described by
considering the more limited field of blood cell counting. Pure
electronic blood cell counters have been developed wherein changes
in conductivity of a diluted blood sample were sensed to provide an
output corresponding to the number of blood cells in the sample.
The more sophisticated of these pure electronic blood cell counters
passed a known volume of diluted blood through an aperture and a DC
electric signal was applied to electrodes positioned at each side
of the aperture to develop a voltage corresponding to the
instantaneous conductivity of the blood sample passing through the
aperture. Since blood cells have extremely low conductivity as
compared to the diluent used to dilute the blood, each time a blood
cell passed between the electrodes, the voltage between the
electrodes would increase and provide a pulse output. The pulses
were counted to provide an output corresponding to the number of
blood cells in the sample.
The problems experienced with aperture-type systems included
clogged apertures resulting from the accumulation of lint and dust
in the aperture and the formation of bubbles which appeared as
blood cells as they bounced around the aperture. In order to detect
aperture clogging and bubble formation, the devices of the prior
art included an oscilloscope to view a trace of the voltage
developed across the aperture so that any abnormality could quickly
be detected. The oscilloscope had to be continuously observed to
determine if clogging was taking place.
Thus, the devices of the prior art required the use of an
oscilloscope to determine if any abnormalities existed that would
adversely effect the blood cell count provided by the instrument.
The inclusion of an oscilloscope in the prior art made their cost
prohibitive and restricted their use to major hospitals and large
laboratories.
SUMMARY OF THE INVENTION
The present invention contemplates a particle counter that may also
be used as a blood cell counter that provides practicing
physicians, veterinarians and laboratories with a simple, reliable
and accurate instrument for counting white and red blood cells. The
instrument automates the tedious task of physically counting
individual blood cells and provides circuitry for automatically
warning the user of such a device when an abnormality is present
that may adversely affect the blood cell count.
The operational concept of the counter is based upon the difference
in electrical conductivity between particles to be counted and the
fluid in which the particles are suspended. When used as a blood
cell counter, the device depends upon the difference in
conductivity between blood cells and the diluent used to prepare
blood samples. The diluted blood sample is drawn through an
aperture so that as individual blood cells pass through the
aperture, the resistance across the aperture abruptly increases. An
rf signal is applied to electrodes on each side of the aperture so
that the signal is modulated by the variation of the resistance
between the electrodes as blood cells pass through the aperture.
The modulated rf signal is coupled to a signal detector where it is
demodulated to provide pulses corresponding to the blood cells
passing through the aperture. The rf frequency is greatly
attenuated by passing the signal through a low-pass filter after
which the pulses are amplified and shaped and then processed
through an amplifier clipper which amplifies the pulses and clips
the base line at a DC bias level. The pulses are then processed
through a counting circuit which includes means for accumulating
and counting pulses and for providing an output corresponding to
the number of blood cells per unit volume which is displayed on a
readout means.
Flow restrictions caused by particulate matter caught in the
aperture cause the resistance across the aperture to approach
exceedingly high levels so that the signal output from the low-pass
filter approximates a DC signal of substantial amplitude sufficient
to trigger a clog alarm driver which has an output to an alarm for
providing a continuous indication which represents a clogged
aperture.
When bubbles form about the aperture, they tend to vibrate back and
forth, causing the resistance across the aperture to fluctuate up
and down by extremely small amounts. This fluctuation results in an
erratic signal output which appears as base line noise and includes
excursions below the 8 volt DC bias level of the amplifier output.
These excursions are used to trigger a transistor that provides an
output for driving a bubble alarm driver. The bubble alarm driver
provides an output to the previously-mentioned alarm which provides
intermittent indications corresponding to the negative excursions
previously mentioned. Thus, a single alarm is used to indicate a
clogged aperture when a constant indication is provided and is also
used to indicate the presence of bubbles when intermittent
indications are provided.
The main objective of the present invention is to provide a blood
cell counter having an alarm system for providing indications of
aperture clogging and the presence of bubbles.
Another objective of the present invention is to provide a blood
cell counter that uses a single indicator to indicate either a
clogged aperture or the presence of bubbles adjacent the
aperture.
Another objective of the present invention is to provide a blood
cell counter wherein a single indicator provides a constant
indication when the aperture is clogged and an intermittent
indication when bubbles are present adjacent the aperture.
The foregoing objectives and advantages of the invention will
appear more fully hereinafter from a consideration of the detailed
description which follows, taken together with the accompanying
drawings wherein one embodiment of the invention is illustrated by
way of example. It is to be expressly understood, however, that the
drawings are for illustrative purposes only and are not to be
considered as defining the limits of the invention.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating the system of the present
invention.
FIG. 2 is a schematic block diagram showing the electrical system
of the present invention.
FIG. 3 is an electrical schematic showing the amplifier clipper
circuit shown in FIG. 2.
DESCRIPTION OF THE INVENTION
The present invention pertains to devices for counting particles
suspended in a fluid medium, wherein the medium and the particles
have substantially different conductivities. The invention will be
described as a blood cell counter, but it is to be understood that
it could be used for counting other types of particles such as dust
or pollution.
Referring to FIG. 1, there is shown a diagrammatic representation
of the system of the present invention. An electrode housing 2
receives a reservoir bottle 4 containing a diluted blood sample 6.
A dip tube 8 extends downwardly from the electrode housing into the
blood sample 6 contained in bottle 4. A cavity 10 is formed in the
upper portion of the electrode housing and is divided into first
and second chambers 12 and 14 by a partition 16 having an aperture
18 formed therein for connecting the first and second chambers. Dip
tube 8 extends into the first chamber 12 of cavity 10 for
communicating bottle 4 with chamber 12. Aperture 18 has a diameter
of 90 microns, a diameter that was chosen because of its
relationship to the size of a normal red blood cell. Electrodes 20
and 22 are mounted in the electrode housing 2 and extend into the
first and second chambers respectively. The electrode housing and
the partition 16 are formed of nonconductive material so that the
electrodes remain electrically isolated from each other and do not
short out through the electrode housing.
A sump bottle 24 has a hollow interior which is in communication
with the second chamber 14 through a flexible tube 26. A vacuum
pump 28 is pneumatically connected with the interior of sump bottle
24 through a flexible tube 30 for evacuating sump bottle 24 so that
the pressure within the bottle is maintained below atmospheric
pressure and the diluted blood sample 6 from the reservoir bottle 4
is drawn through dip tube 8 and into the first and second chambers
12 and 14 so as to establish a flow of blood sample through
aperture 18.
Electronic circuitry 34 impresses an rf signal across the
electrodes to develop a voltage across the electrodes dependent
upon the instantaneous conductivity of the diluted blood sample
passing through the aperture.
Blood cells have substantially lower conductivity than the diluent
used for diluting the sample and therefore, abrupt voltage
increases or pulses are generated each time a blood cell passes
through the aperture. The electronic circuitry 34 senses the pulses
and processes them to provide an output corresponding to the number
of blood cells per cubic millimeter of blood sample passing through
the aperture. This output is displayed on a readout device 36, such
as a meter.
Referring to FIG. 2, there is shown a schematic diagram of the
overall electronic circuitry of the instrument of the invention. A
multivibrator 38 provides a squarewave output at a frequency of 330
KHz with a 20 volt peak output. The output of multivibrator 38 is
connected to a signal detector 40 through a resistor 41. The input
of the signal detector is connected to electrode 22 of the
electrode housing 2 while electrode 20 is connected to ground.
A voltage divider is formed by resistor 41 and the resistance
across electrodes 20 and 22 so that the 330 KHz signal supplied by
multivibrator 38 is modulated as the resistance across the
electrodes increases when a blood cell passes through the aperture.
Signal detector 40 functions as a demodulator and amplifier to
provide a rectified signal to a low-pass filter 42 which eliminates
the rf component of the signal. The low-pass filter is a 6 pole
Butterworth Filter which passes frequencies below 33 KHz;
therefore, the output of the low-pass filter is a series of pulses
corresponding to blood cells passing through the aperture. The
filter output pulses are provided to an amplifier shaper 44 for
pulse amplification. The output of amplifier shaper 44 is connected
to the input 46 of an amplifier clipper 48 which has an output 50
for providing pulses having an amplitude of approximately 4 to 6
volts at a bias of 8 volts DC.
The output so of amplifier clipper 48 is connected to a counting
circuit 52 which includes a counting means for accumulating and
counting the pulses received from the amplifier clipper and for
providing an output signal corresponding to the number of pulses
counted. The output of counting circuit 52 is connected to a
readout device 54, such as a meter for providing an indication
corresponding to the number of blood cells per unit volume of blood
sample.
A clog alarm driver 56 is connected to the output of the low-pass
filter 42 and comprises a transistor biased to turn on at a
predetermined voltage level. The clog alarm driver has an output
connected to an alarm 58, such as an indicator light which in
response to the output provides an indication. When the aperture
becomes clogged, the resistance across the aperture increases
substantially so that the rf carrier signal increases in amplitude
resulting in a high level DC signal from the low-pass filter that
exceeds the predetermined voltage level at which the clog alarm
driver turns on. Since a clog is a constant condition, the DC level
remains constant and the alarm provides a constant indication.
Amplifier clipper circuit 48 has a second output 62 which is
connected to a bubble alarm driver 60 which in response to an
output signal from the amplifier clipper provides an output to
alarm 58 causing the alarm to provide an indication. The bubble
alarm driver is a standard driver circuit that provides an output
in response to an input signal.
Referring to FIG. 3, there is shown a schematic diagram of the
amplifier clipper circuit 48 shown in FIG. 2. Terminal 46 is
connected to the non-inverting input of an operational amplifier
64. Series connected resistors 66 and 68 are connected between a 28
volt DC source and ground to form a voltage divider for
establishing a DC bias level at the junction between the two
resistors. A resistor 70 connects the junction between the
resistors 66 and 68 to the non-inverting input of amplifier 64. The
output of amplifier 64 is connected to terminal 50 of the amplifier
clipper circuit and in addition thereto, it is connected to the
inverting input of amplifier 64 by a feedback loop consisting of a
resistor 72 and a potentiometer 74 for providing a variable
resistance in the feedback loop. A series connected resistor 76 and
capacitor 78 are connected between the inverting input of amplifier
64 and ground. A transistor 80 has an emitter connected to the
inverting input of amplifier 64, a base connected to the output of
amplifier 64 and a collector connected to output 62 of the
amplifier clipper circuit. A resistor 82 and a capacitor 84 are
connected in parallel between the collector of transistor 80 and
ground.
In operation resistors 66 and 68 are adjusted to that an 8 volt DC
bias is established at the output of amplifier 64 and potentiometer
74 is adjusted so that the pulses are 4 to 6 volts in amplitude
above the 8 volt DC base line. In normal operation, transistor 80
remains in a cut off condition since the base is subjected to a
higher voltage than is the emitter. When bubbles are formed
adjacent the aperture, they tend to vibrate about the aperture
prior to passing through the aperture. The vibrating bubbles cause
the aperture resistance to fluctuate by an extremely small amount
such as 0.1 per cent. This fluctuation appears as base line noise
on output 50 of amplifier clipper 48. The noise includes excursions
below the 8 volt DC base line. The negative excursions cause
transistor 80 to turn on thereby clipping the negative going
signals. The current through transistor 80 when it turns on is
sensed by resistor 82 and capacitor 84 and causes capacitor 84 to
become charged. If a oscillating bubble is present, a continuous
train of negative going signals is produced so that capacitor 84
receives a continuous train of charges and develops a voltage which
appears on terminal 62 of the amplifier clipper circuit and is used
to drive the bubble alarm driver 60 when a specified threshold
voltage is exceeded.
Thus, when bubbles are formed adjacent the aperture, intermittent
output signals are provided to the bubble alarm driver so that the
alarm 58 provides an intermittent flashing indication indicative of
the presence of bubbles as distinguished from the constant
indication which is indicative of a clogged aperture. The present
invention provides an inexpensive circuit for providing alarms that
indicate the presence of bubbles adjacent the aperture or the
existence of a clogged aperture and thereby eliminates the
necessity for the use of an oscillosclope as required by the prior
art devices. The circuit makes it possible to use a single alarm
indicator for providing indications of both aperture clogging and
bubble formation.
* * * * *