U.S. patent number 3,878,567 [Application Number 05/481,578] was granted by the patent office on 1975-04-22 for self-contained artificial heart.
This patent grant is currently assigned to Atlantic Richfield Company. Invention is credited to David L. Purdy.
United States Patent |
3,878,567 |
Purdy |
April 22, 1975 |
Self-contained artificial heart
Abstract
A small, self-contained blood pump includes a
physiologically-responsive beat rate control system and a pulmonary
edema protection system.
Inventors: |
Purdy; David L. (Indiana,
PA) |
Assignee: |
Atlantic Richfield Company (Los
Angeles, CA)
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Family
ID: |
26796302 |
Appl.
No.: |
05/481,578 |
Filed: |
June 21, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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99635 |
Dec 18, 1970 |
3828371 |
|
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Current U.S.
Class: |
623/3.19;
128/899 |
Current CPC
Class: |
A61M
60/50 (20210101); A61M 60/40 (20210101); A61M
60/871 (20210101); A61M 60/122 (20210101); A61M
60/268 (20210101); A61M 60/148 (20210101); A61M
2205/3334 (20130101) |
Current International
Class: |
A61M
1/10 (20060101); A61M 1/12 (20060101); A61f
001/24 () |
Field of
Search: |
;3/1,DIG.2,1.7
;128/1D,DIG.3 ;417/394,395,321,460,468 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"An Electronic-Mechanical Control for an Intrathoracic Artificial
Heart," by K. W. Hiller et al., American Journal of Electronics,
July-Sept., 1963, pages 212-221. .
"Development of an Artificial Intrathoracic Heart," by C. K. Kirby
et al., Surgery, Vol. 56, No. 4, Oct., 1964, pages 719-725. .
"The Development of an Intrapericardial Replacement," Transactions
A.S.A.I.C., Vol. XII, 1966, pages 272-274..
|
Primary Examiner: Frinks; Ronald L.
Attorney, Agent or Firm: Ewbank; John R.
Parent Case Text
RELATED APPLICATIONS
This is a division of U.S. Pat. No. 3,828,371, derived from Ser.
No. 99,635 filed Dec. 18, 1970.
Claims
I claim:
1. A self-contained implantable artificial heart comprising:
a source of electric power;
a reciprocating device, said device having a reciprocally movable
portion and a stationary portion;
artificial left and right artificial ventricles arranged so that
when said reciprocally movable portion moves in one direction, said
ventricles are simultaneously compressed to expel blood
therefrom;
electric control circuits comprising sensing means adapted to
generate an electrical signal indicative of blood pressure,
electronic means converting the blood pressure signal to a filtered
smoothly varying potential indicative of average blood pressure,
said average blood pressure potential being applied simultaneously
to a multivibrator to regulate the frequency of reciprocation of
the reciprocating device throughout a range of rate of stroke
within the range of healthy pulse rate, and to a control to affect
a similar regulation of the stroke of the reciprocating device,
whereby the range of pumping capacity of the ventricles is
significantly greater than the range of stroke rate;
a housing enclosing said source reciprocating device, control
circuits, and ventricles, said housing being of a size to fit
within the chest cavity after removal of a major portion of the
natural heart.
2. The device of claim 1 in which the electrical control means
includes sensing means to determine average pulmonary blood
pressure, an electromagnetic valve at the blood inlet to the right
artificial ventricle adapted to control the time when blood may
enter said right ventricle, said control means being adapted to
hold said valve closed when said average pulmonary blood pressure
is sensed to be above a predetermined level.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to a single unit mechanical device
capable of circulating blood in the human body in place of a human
heart and capable of surgical implantation in the thoracic cavity
in a single operation.
2. Description of the Prior Art
Previous nuclear powered mechanical heart devices such as the one
shown in U.S. Pat. No. 3,379,191 of Apr. 23, 1968, were comprised
of two separate units, one to be implanted in the thoracic cavity
and a separate power source unit to be implanted in the abdominal
cavity with a connecting line to pass the steam generated at the
boiler unit of the power source and return the used steam to a
condenser and then back to the power source. Another disadvantage
of the prior art devices was that the artificial ventricles were
mechanically coupled to the reciprocating piston and when the
piston drew blood into the ventricles, the atrial system tended to
collapse under the negative pressure induced therein. Adequate
precautions were not taken against pulmonary edema which resulted
from continuous pumping of blood to the lungs beyond capacity of
the blood vessels therein. Although prior art devices could be set
at a selected beat rate, no one has previously conceived of means
for varying the beat rate or blood pump output of an implantable
artificial heart according to the body's need for blood as a
natural human heart does.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a single
unit artificial heart device having an integral energy source and
controls adapted to be implanted in the pericardial sac in place of
a human heart.
It is a further object of this invention to provide an artificial
heart having a thermoelectric module allowing close simulation of
the functions of a human heart by electrical control of pumping
rate and pulmonary to systemic pumping ratio in response to
physiological need.
Another object is to provide an artificial heart which is more
efficient and longer lasting than previous devices.
Another object is to provide an artificial heart which is lighter
than previous devices.
Other objects of this invention will become apparent from the
description of the invention which follows.
Broadly, the invention is a self-contained artificial heart
including an electronic control circuit adapted to simulate a
natural heart's action by varying the pulse and flow rate in
response to a physiological variable.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal section taken approximately on the line
1--1 of FIG. 2 of a self-contained artificial heart constructed in
accordance with one embodiment of the invention;
FIG. 2 is a cross-section taken on the line 2--2 of FIG. 1;
FIG. 3 is a fragmentary plan view of the left hand end portion of
FIG. 1;
FIG. 4 is a diagrammatic one half plan view taken on the line 4--4
of FIG. 2;
FIG. 5 is a part sectional and part elevational view illustrating
the piston and cylinder and associated right and left artificial
ventricles in compressed position;
FIG. 6 is a circuit diagram of the beat rate and stroke length
control system;
FIG. 7 is a circuit diagram of the right ventricle blood inlet
valve control system;
FIG. 8 is a circuit diagram of the feedliquid pump control system;
and
FIG. 9 is a schematic of the electrical and working fluid flow
system.
DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED
EMBODIMENTS
Referring to the drawings which show an illustrative embodiment of
the blood pump device of the invention, the device 10 contains a
source of thermal energy 11 preferably a radioisotope and most
preferably a compound of plutonium.sup.238. A thermoelectric
converter 12 is in proximity to the thermal energy source 11 and
functions to convert a first portion of the thermal energy from Pu
compound 11 to electrical energy. Also in close proximity,
preferably surrounding the source of thermal energy and most
preferably surrounding the converter 12, is a monotube boiler 13
which functions to vaporize and superheat the working fluid. The
working fluid may be any one suitable for use in a Rankine cycle
engine such as hydrocarbon, halogenated hydrocarbons such as that
family of compounds known as the "Freons," or water. The working
fluid is changed from its liquid to its gaseous state in the boiler
13 by a second portion of the thermal energy and is passed to an
expansion zone 14 established by stationary piston 15 and
reciprocally movable cylinder head assembly 16 through a solenoid
controlled inlet valve 17 in said stationary piston 15. The
stationary piston 15 also contains a solenoid-operated exhaust
valve 18. The cylinder head assembly 16 moves first away from the
piston 15 when the inlet valve 17 is opened and the exhaust valve
18 is closed, and second toward the piston 15 when the exhaust
valve 18 is opened and the inlet valve 17 is closed. When the
cylinder head assembly 16 is moving away from the stationary piston
15, it compresses an artificial right ventricle 19 and an
artificial left ventricle 20 simultaneously to expel blood
therefrom by means of a pusher plate member 21--21 which is
attached to the cylinder head 16 but is preferably not physically
attached to the ventricles 19 and 20. When the cylinder head 16 is
moving back toward the piston 15, it causes the pusher plate 21--21
to move away from the ventricles 19 and 20, allowing them to expand
and allow blood to enter naturally as indicated by arrows 23 and 22
(respectively for ventricles 19 and 20) in FIG. 3; that is, as a
result of the pressure in the atrial system and not as a result of
the negative pressure which would be caused if the pusher plate 21
were attached directly to the ventricles 19 and 20 and forced them
open. When the ventricles 19 and 20 are compressed as shown in FIG.
5 as a result of the force of cylinder head assembly 16, blood is
caused to be expelled as indicated by arrows 24 and 25
(respectively for ventricles 19 and 20) in FIG. 3 into both the
systemic and the pulmonary systems of the mammal in which the blood
pump 10 is implanted.
By transmitting the engine cylinder force directly to the blood, a
pulse shape very similar to that of the human heart can be
obtained, resulting from the high initial force as gas initially
enters the cylinder and rapidly decreasing as the engine cylinder
moves. Blood, indicated by the arrow 25 from the left artificial
ventricle 20, is passed to a connection 26 to the patient's aorta
while blood 24 from the right artificial ventricle 19 is passed to
a specially designed pulmonary artery connection 27 containing an
outlet valve 28. The inlet 29 to this right artificial ventricle 19
preferably contains an electromagnetically controlled valve 30 to
be described in more detail later in the specification. The aorta
connection 26 also contains a valve 31 to prevent backflow of blood
25 in the opposite direction. The left ventricle 20 also contains a
blood inlet valve 32 which allows blood 22 only to enter the left
ventricle 20.
The aorta connection 26, pulmonary artery connection 27, left and
right artificial ventricles 20 and 19 are constructed of any
suitable medical grade material which is compatable with blood and
body tissues. Natural and synthetic polymer materials such as
polyurethane, dacron, hepranized silastic, and silicon polymers are
merely exemplary; the particular material selected does not form a
part of the present invention.
A capillary condenser tube 33 is connected to the piston exhaust
valve 18 and preferably has an inner surface lined with a fibrous
metal wick 34. For example, such a wick-type of capillary lining
may be formed from sintered titanium-aluminum-vanadium alloy.
Exhaust vapor entering the condenser tube 33 at 36 (FIG. 9)
condenses on the porous wick 34 and fills the wick pores. The
condensate flows through the wick 34 to the exit 35 (FIG. 9) of the
condenser and then through a subcooler 37 (FIG. 4) to the inlet 38
of the feedliquid pump 39. The condensate is retained in the wick
by capillarity regardless of the position or attitude of the heart
device. The capillary condenser 33 has a large surface area and
rejects heat to an interstitial fluid 43 (FIG. 1) which in turn
rejects its heat to the blood in the ventricles 19 and 20 and
maximizes the distribution of heat while minimizing the blood
temperature rise. The feedliquid pump 39 is preferably driven by an
electrically operated solenoid 40 driven by an electronic control
system shown in FIG. 8 at a constant rate. From the feedliquid pump
39 the working fluid is passed back to the boiler 13 where it is
vaporized again.
The availability of the electric power from the thermoelectric
module or converter provides for electronic control of various
functions of this artificial heart which make it superior to any
prior art artificial heart. The thermoelectric module 12 is
preferably a series of silicon-germanium semi-conductor
thermocouples. The thermoelectric converter 12 provides electricity
to electrical control circuits (shown in FIG. 6) which control the
electromagnetic gas inlet valve 17 and the electromagnetic exhaust
valve 18 in the piston 15 and which function to control precisely
either or both the stroke length and the cylce rate of the movable
cylinder head assembly 16. In the preferred embodiment, the
electrical control circuit (FIG. 6) is adapted to vary the pulse
rate and the stroke length in response to a physiological variable
such as blood pressure, variations in which are detected by means
of a sensor such as a pressure sensitive transistor thereby varying
the rate of pumping of blood in response to the physiological
variable, closely simulating the behavior of a natural human
heart.
The converter 12 also provides electricity for another electrical
control circuit (shown in FIG. 7) which is preferably provided to
control an electromagnetic valve 30 at the blood inlet 29 to the
right artificial ventricle 19 and is adapted to control the amount
of blood indicated by arrow 23 (FIG. 3) entering the right
ventricle 19. A sensor (not shown) of pulmonary blood pressure is
provided which signals the control circuit (FIG. 7) when the
pulmonary blood pressure rises above a predetermined level and
causes the electromagnetic valve 30 to be closed until the
pulmonary blood pressure drops to an acceptable level. Pulmonary
edema is thereby effectively prevented because of the artificial
heart's adaptability to change the systemic system to pulmonary
system pumping rate ratio.
Since the rate of blood pumping and hence flow of working fluid
through the cylinder may be varied, and the feedliquid pump 40
preferably operates at a constant rate, there will be excess vapor
during the major portion of normal activity and during periods of
low blood flow power demands. A relief valve 45 (FIG. 9) is
provided to release excess vapor from the boiler superheater 46
into the condenser 33 at 36 at a predetermined pressure.
The source of thermal energy 11 previously mentioned is preferably
a compound of Pu.sup.238 isotope and is shielded preferably by a
platinum capsule 41 having an absolute filtered vent 42 (FIG. 1) to
duct helium generated by said isotope 11 during the course of this
decay directly into the interstitial fluid 43. The helium permeates
the silastic covering 44 (FIG. 1) into the bloodstream. A
microsphere fuel form is coated first with thoria and then with
platinum-rhodium to form a ductile mass which withstands any
credible impact as well as fire or any credible accident.
An internal cylindrical bellows 47 and an external cylindrical
bellows 48 (FIGS. 1 and 2) are provided, one end of each being
welded to the movable cylinder head 16 and the other end of each
being welded to a stationary member 49 which is affixedly attached
to the piston 15. The internal bellows 47 forms a hermetic seal to
prevent any possible working fluid escape and to vent any vapor
leakage past the cylinder 14 directly to the condenser 33. In the
preferred embodiments, there is provided a xenon-filled annular
chamber defined by bellows 47 and 48. Much of such annular chamber
is occupied by thermally insulating, slidably interfitting Min-K
cylindrical cans 50 and 51 which act as thermal insulators.
Surrounding this annulus is the external bellows 48 which provides
a hermetic seal for xenon 52 containment. Xenon 52 provides the
dual function of lowering the thermal conduction of the annulus and
generating a null force on the piston 15 when the cylinder 14 is at
its smallest volume. With the movement of the cylinder head
assembly 16 away from the piston 15, the two bellows 47 and 48 are
lengthened and the xenon pressure reduces, thereby increasing the
propensity of the gas pressure forces other than the working fluid
pressure to urge the cylinder head assembly 16 toward the position
providing the smallest volume for expansion zone 14. As the
cylinder head assembly 16 advances, it asserts a direct force onto
the two artificial ventricles 19 and 20, thereby expelling the
blood. At the completion of the pump stroke the pressure in the
cylinder will have dropped and the exhaust valve 18 will open for
at least a portion of the return stroke.
DESCRIPTION OF CIRCUITRY
The artificial heart is controlled by circuitry responsive to some
physiological function such as the average blood pressure, filtered
to eliminate the variations from beat to beat. In FIG. 6, dotted
lines enclose certain electronic functions, which have
inter-relationships shown by the schematic diagram. A variable
voltage signal indicative of the variations in blood pressure is
regulated by the "Right Atrial Pressure Sensor" unit, there being a
suitable transducer in the right atrium. The human body is thus a
significant participant of the feedback loop.
Particular attention is directed to the feature whereby this
average blood pressure signal varies both the stroke and the rate
of the artificial heart, thus simulating the normal heart's
capacity for increasing both the volume per beat and the rate of
the pumping action. That portion of FIG. 6 within the dotted lines
identified as "Rate Control" is a multivibrator, the rate of which
is controlled by the average blood pressure. The "Gas Inlet
Control" is an emitter coupled monostable vibrator, the pulse width
of which is varied by the average blood pressure. The train of thus
regulated pulses actuates a driven circuit identified as a "Gas
Inlet Switching Network" whereby the gas inlet valve 17 solenoid is
energized to control both the stroke and the rate of the
reciprocating cylinder head assembly 16. The exhaust valve 18 is
regulated by a solenoid energized through a "Gas Exhaust Switching
Network" driven by the signal from the "Gas Exhaust Control," the
frequency of the pulses being the complimentary output of the "Rate
Control" regulated by the feedback signal from the human body
through the "Right Atrial Pressure Sensor."
The current from the thermoelectric converter 12 energizes the
circuits of FIGS. 6, 7, and 8. Within each set of dotted lines, any
transistor described as a second transistor is the one on the
right, the leftward transistor being called the first
transistor.
The reciprocation rate of the cylinder head assembly 16 is
controlled by the rate at which the inlet valve 17 is opened. A
less than maximum stroke length is achieved by shortening the
duration of the opening of the inlet valve 17. The exhaust valve 18
is electrically actuated toward the open position during at least
some portion of the cycle when the intake valve is not so
actuated.
The gas inlet valve solenoid is controlled by a "Gas Inlet
Switching Network." A "Gas Inlet Control" is an emitter-coupled
monostable vibrator whose pulse is triggered by the train of pulses
from the "Rate Control," the pulse width being varied by the signal
from the "Right Atrial Pressure Sensor." Thus, when the body sends
back more blood toward the heart, the pumping capacity is increased
in part as a result of increasing the stroke by increasing the
pulse width.
The "Gas Inlet Switching Network" is a driver circuit comprising a
first and second transistor. A positive current is directed through
a diode, a resistor, the solenoid coil for the inlet valve 17 and
the collector and emitter of the second transistor. The base of the
second transistor is controlled by the emitter signal from the
first transistor developed across a resistor voltage divider. The
emitter of the second transistor is also connected by two parallel
capacitors to the collector through the solenoid winding in the
valve 17 for the gas inlet. A diode in parallel with the solenoid
winding for the valve 17 of the gas inlet serves to prevent any
adverse effects from the intermittent potential in the solenoid. In
the operation of the "Gas Inlet Switching Network", the low power
signal from the "Gas Inlet Control" regulates both the frequency
and duration of valve opening, and the switching network unit
controls the flow of the higher power current to the solenoid of
the valve 17.
The "Gas Inlet Control" is an emitter-coupled monostable vibrator
and includes two common emitter connected transistors, the emitters
being maintained above ground by a resistor to ground. The base of
a first transistor of the "Gas Inlet Control" is connected through
a resistor to the collector of the second transistor, which
provides an output signal from the "Gas Inlet Control." The
collectors of the first and second transistors of the gas inlet
control are connected through their respective resistors to a
positive potential. The signal on the collector of the first
transistor is coupled to the base of the second transistor through
a capacitor. The pulse width is increased when the heart rate is
increased because the "Gas Inlet Control" is modulated by the
output signal of the right atrial pressure sensor. For example,
such atrial signal can be connected through a resistor to the base
of the second transistor.
The "Rate Control" unit is an R-C coupled common emitter
multivibrator. The base of each transistor is connected by a
capacitor to the collector of the other transistor and by a
resistor to the positive signal from the "Right Atrial Pressure
Sensor." Similarly, the collector of each transistor is connected
through a resistor to such positive signal from the "Right Atrial
Pressure Sensor".
The operation of the "Rate Control" unit can be clarified by noting
that a positive signal from the "Right Atrial Pressure Sensor" is
converted by the multivibrator to two trains of pulses at a rate of
the general magnitude of a natural heart beat, the pulses from one
side of the multivibrator being directed to the "Gas Exhaust
Control" and the other train of pulses from the other side of the
multivibrator being directed to the "Gas Inlet Control." The
frequency of the multivibrator increases when the body needs more
blood circulation as communicated by the positive signal from the
"Right Atrial Pressure Sensor."
The "Right Atrial Pressure Sensor" includes a transducer responsive
to the pressure in the right atrium, such transducer being
associated with the base of the transistor in such unit. A voltage
divider between the positive terminal of the source of electrical
potential and ground provides a controlled voltage to the base. The
emitter of the transistor is connected by a resistor to ground. The
collector is connected by a resistor to the positive terminal of
the source of electrical potential. The output signal at the
collector is coupled to supply the positive potential for the
multivibrator by an isolating diode in series with a resistor. A
capacitor is connected between such resistor and ground. Such
association of the electronic components in the unit designated as
the "Right Atrial Pressure Sensor" provides a filtered signal (the
beat to beat variations being rejected) which is a smoothly varying
positive signal indicative of average atrial pressure, and this
signal regulates the variations of both the "Rate Control" unit and
the "Gas Inlet Control" for controlling both the rate and stroke of
the reciprocations of the cylinder head assembly 16. In this
manner, the entire system closely simulates the response of a
natural heart to right atrial pressure.
The "Gas Exhaust Control" is similar in configuration and operation
to the "Gas Inlet Control." A signal consisting of a train of
pulses from the multivibrator is applied to the base of the first
transistor. The bias, however, is derived directly from the
positive potential source, rather than from the positive output of
the "Right Atrial Pressure Sensor" because the working fluid can
flow through an open exhaust valve during the same fraction of a
cycle without regard to whether the inlet valve was long open for a
full stroke or a shorter time for a partial stroke.
The "Gas Exhaust Switching Network" includes a transistor, the base
of which is connected through a resistor to ground. The solenoid
coil operating the gas exhaust valve is connected in series with
the collector to the positive potential source. A diode bypasses
the solenoid coil of the gas exhaust valve 18 to protect the
transistor from a voltage spike when the solenoid current is
interrupted.
In the operation of the circuitry of FIG. 6, the pressure sensor at
the right atrium provides a positive signal upon which is impressed
the collector voltage developed by the base current generated by
the right atrial pressure. The pulse rate of the "Rate Control" is
controlled by the voltage of the "Right Atrial Pressure Sensor" to
provide a train of pulses to the "Gas Inlet Control" and the "Gas
Exhaust Control." The respective gas inlet and exhaust switching
networks are operated by their controls so that the valves are
actuated at rates determined by the pressure in the right atrium,
and the inlet switching network is additionally controlled to
narrow the proportion of maximum pulse width sent to the gas inlet
valve solenoid coil except when a predetermined high pressure of
the right atrium is exceeded. Thus, as the body sends back blood to
the heart at a greater rate, the heart's pumping capacity is
increased by increasing both the stroke of the cylinder head
assembly 16 and the frequency or number of strokes per minute.
FIG. 7 depicts a "Pulmonary Edema Protector" and is effectively a
blood switching system which prevents the flow of blood to the
lungs during those periods when the average pulmonary blood
pressure is excessive. When the pulmonary, arterial, average
pressure rises above a predetermined value, the Schmidt trigger
changes state and closes blood inlet valve 30 by which the blood
would flow to the lungs through the right ventricle. The "Pulmonary
Edema Protector" includes two transistors, the emitters of which
are connected together and maintained above ground potential by a
resistor. Each collector is connected through a resistor to the
positive terminal, and the bases are each biased by a resistor to
ground. The input signal is coupled through a resistor from the
"Pulmonary Arterial Pressure Sensor" to the base of the first
transistor, and the output signal from the collector of the first
transistor is coupled by a resistor to the base of the second
transistor.
The signal at the collector of the second transistor of the
"Pulmonary Edema Protector" is coupled through a resistor to the
base of the single transistor in the "Blood Inlet Switching
Network," a circuit similar to the "Gas Exhaust Switching Network"
described above with respect to FIG. 6.
In operation, the opening or closing of the right ventricle blood
inlet valve 30 is controlled by the "Blood Inlet Switching
Network." Such valve is closed in response to any signal from the
"Pulmonary Edema Protector," which signal is sent only during the
brief moments when the pulmonary arterial pressure exceeds the
predetermined limit. The "Pulmonary Edema Protector" protects the
system so that the lungs are protected from blood circulation rates
greater than the lungs can at that moment satisfactorily process,
even when the flow of blood back to the heart might suggest a
greater circulation rate. Thus, the inlet valve 30 for the blood
for the right ventricle is closed during those moments appropriate
for responding to the ability of the lungs to process such rate of
blood circulation, but is open much of the time.
In FIG. 8, the voltage source is conducted through a zener diode
voltage stabilizer to a feedliquid "Pump Rate/Duration Control," a
multivibrator comprising two transistors of opposite conductivity
type. The emitter of the first transistor is connected directly to
the positive potential. The collector of the second transistor is
connected by a resistor to such positive potential. The collector
of the first transistor is connected through a resistor, and the
emitter of the second transistor is connected directly to ground.
The bases of the two transistors are interconnected by a
symmetrical network, each including a base-to-collector resistor
and a capacitor and resistor in series between the base of one
transistor and the collector of the other. The feedliquid "Pump
Switching Network" is essentially of the same configuration and
operation as the "Gas Inlet Switching Network" of FIG. 6.
In the operation of the circuitry of FIG. 8, the oscillator of the
rate control unit provides a train of pulses of controlled duration
which actuate the heavy duty switching of the switching network
unit to energize the solenoid 40 to operate the pump 39 at a
predetermined constant rate. By appropriate choice of the resistors
in the symmetrical base-collector network of the feedliquid pump
rate/duration control, the relative time between adjacent pulses as
well as the pulse duration can be readily controlled.
The embodiments of this invention described in great detail are
merely illustrative of the invention. Certain obvious modifications
might eventually be apparent to those skilled in this art without
departing from the spirit and scope of the invention as set forth
in the claims.
* * * * *