 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates to an automatically operated non-invasive blood
pressure measuring and recording system, and more particularly to a system
of the type which includes an inflatable cuff for encircling a portion of
the human body, usually the arm, means for inflating and deflation the
cuff for selectively occluding an arterial vessel, means such as a
microphone for detecting flow variations through the vessel as the cuff is
delfated, e.g., those variations giving rise to Korotkov sounds identified
with the systolic and diastolic pressures, and means for recording arm
cuff pressure values in correspondence with the detected flow variations
to provide a measurement record.
2. Description of the prior art
In known blood pressure systems the inflation of the pressure cuff is
obtained by the operation of either a hand operated pump or an electric
pump which is turned off when the desired pressure is reached. Deflation
is accomplished with an air escape valve controlled either manually or
with a servomechanism, as disclosed in U.S. Pat. No. 3,905,353, to provide
a more or less constant rate of pressure drop. These known techniques have
not been fully satisfactory, as they either are substantially nonlinear or
require complicated means to approach linearity, and as they are affected
by ambient conditions and do not provide the reproducability of pressure
drop necessary for accurate, repeatable measurements. In addition, such
techniques are not readily adaptable to provide a slower linear rate of
pressure drop in the particular regions where systolic and diastolic
pressures are detected, as suggested for improved measurement accuracy in
U.S. Pat. No. 3,814,083 (col. 3, 1. 28-40). Finally, such inflation and
deflation techniques do not lend themselves easily to automatic control
over a full inflation and deflation cycle, which is desirable from the
standpoints of reproducability of measurement and ease of operation.
In addition, known blood pressure systems provide a limited amount of
measurement and diagnostic information, either in the form of chart traces
of flow variations to be interpreted visually (e.g., U.S. Pat. Nos.
3,811,439, 3,867,926 and 3,878,834), in the form of readouts, either
digital or analog, of systolic and diastolic pressures (e.g., U.S. Pat.
Nos. 3,085,567, 3,396,405, 3,905,354, 3,623,476 and 3,500,822), or in the
form of aural signals to be interpreted traditionally by a physician for
the onset and disappearance of Korotkov sounds. Known systems heretofore
have not provided multiple sources of information simply and easily, and
have not included any arrangement permitting a diagnosis of the action of
the artery,e.g., for detection of murmurs and the like, in connection with
the blood pressure measurement.
Finally, known automatic blood pressure systems seeking to provide a high
degree of automation have been complicated and expensive, and accordingly
have failed to realize the potential economies of use by inexperienced or
untrained operators.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide an improved
automatic blood pressure measuring and recording system of the inflatable
cuff type which is more suitable for clinical use. A further object of the
invention is to provide such a system with an improved cuff inflation and
deflating means which is capable of providing a linear, repeatable rate of
pressure decrease for accurate measurement, which is adapted to be easily
and automatically controlled, and which permits use with a variety of
different cuff sizes. Still other objects of the invention are to provide
such a system which is capable of generating a variety of measurement and
diagnostic information, which is relatively simple and inexpensive to
construct, and which is easy to use even by unskilled operators.
In a preferred embodiment of the invention to be described hereinbelow in
detail, the blood pressure measuring and recording system includes
improved means for inflating and deflation a cuff in the form of a
reversible single stroke sleeve diaphragm pump defining a contained air
space variable in volume. A motor, operating at a selected constant speed,
drives a piston in the pump to linearly vary the volume of the contained
air space and thereby linearly vary the pressure in the cuff. Motor speed
control means, responsive to a manual start switch and limit switches on
the pump, automatically operate the motor to inflate and deflate the cuff
in a linear, reproducable manner. Preferably, the motor speed control
means is further responsive to detected flow signals to change the pump
motor speed to a lower constant rate in selected pressure regions to
enhance accuracy of measurement.
In another aspect of the invention, an adjustable ballast tank is
pneumatically coupled to the cuff and pump to accommodate different cuff
volumes while permitting a small and economical pump to accomplish desired
pressure changes.
In a further aspect of the invention, blood pressure measurements are
recorded by a recording mechanism having a linear pneumatic actuator which
receives the linearly varying cuff pressure to move a member carrying a
recording pen and pen driver over a calibrated chart, and at the same
time, to vary an electrical element, such as a resistance, to provide an
electrical signal varying with cuff pressure. A detector, such as a
microphone, provides a signal varying with the flow through the arterial
vessel, and the detected signal is applied to the pen driver to provide a
continuous trace on the calibrated chart as cuff pressure is decreased.
At the same time, the detected signal is applied to a signal analyzer
arranged to provide outputs at the systolic and diastolic pressures, and
the analyzer output signals are applied to the pen driver, to record the
systolic and diastolic pressures on the calibrated chart. In addition, the
detected signal is applied to an audio circuit to provide a high fidelity
representation of arterial flow for diagnosis of specific kinds of
arterial flow variations due to heart murmurs and the like, while a
measurement is in progress. If desired, the electrical signal varying with
cuff pressure and the analyzer output signals may be correlated in an
auxiliary display, e.g., a digital display, to indicate the numerical
values of the systolic and diastolic pressures. Thus temporary records on
the display, permanent records on a calibrated chart, and an aural
diagnostic signal all may be obtained as desired using the same equipment.
Other objects, aspects and advantages of the invention will be pointed out
in, or be apparent from, the detailed description hereinbelow, considered
together with the following drawings.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is an essentially diagrammatic view of a blood pressure measuring
and recording system constructed according to the present invention;
FIGS. 2-4 are views of the inflating and deflating means shown in FIG. 1,
FIG. 2 being a plan view, FIG. 3 a section on line 3--3 of FIG. 2, and
FIG. 4 an end elevation with portions shown in phantom for clarity;
FIGS. 5-7 are views of the pneumatic recording actuator shown in FIG. 1,
FIG. 5 being a side elevation, FIG. 6 a section on line 6--6 of FIG. 5,
and FIG. 7 a partial section on line 7--7 of FIG. 5; and
FIG. 8 is a schematic diagram of the speed control means shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, FIG. 1 illustrates in diagrammatic form an
automatic blood pressure measuring and recording system constructed in
accordance with the present invention. The individual whose blood pressure
measurement is to be taken is noninvasively coupled to the system through
an inflatable cuff 10 and a microphone 12. The inflatable cuff 10 fastens
around the individual's arm and, upon inflation and deflation, selectively
occludes a brachial artery for measurement of the blood pressure therein.
Adjacent the cuff 10, or mounted thereon, the microphone 12 detects sounds
from the selectively occluded artery arising from flow variations therein
and generates an output, amplified by an amplifier 14, to provide an
electrical detection signal Vd. In the manner described below, after the
cuff 10 and microphone 12 are in place, and a start switch 16 is closed,
the system automatically performs a blood pressure measurement process
correlating the cuff pressure with the detection signal to yield
measurement records on a calibrated chart 18, a display 20, or both. At
the same time, an aural representation of the flow variations is provided
on a loudspeaker 22 for detection of particular variations arising from
heart murmurs and the like.
As shown in FIG. 1, the cuff 10 is pneumatically coupled by means of a
suitable conduit 24 to a pressure source 26 which, in accordance with the
present invention, inflates and deflates the cuff over a pressure range
providing the desired arterial occlusion. The pressure source 26, to be
described below in greater detail with reference to FIGS. 2-4, comprises a
fixed volume single stroke reversible piston pump 28 and an electric motor
30 operating at a selected constant speed for advancing and retracting the
piston drive shaft 31 at a selected linear rate to cause a linear pressure
increase and decrease in cuff 10. The speed of motor 30 is under the
control of a speed controller circuit 32, to be described below in greater
detail with reference to FIG. 8.
Briefly, the speed controller 32 has an input from start switch 16 to cause
motor 30 to start a forward (inflating) stroke of drive shaft 31. An input
from a manual reverse switch 34 is provided to reverse motor 30 to permit
the measurement process to be aborted at any time during the measurement
if desired. When the forward stroke of pump 28 is completed, and full
inflation of cuff 10 is achieved, an upper limit switch 36 is tripped
automatically by pump 28 to cause the controller 32 to reverse motor 30
and begin the reverse (deflating) stroke of piston drive shaft 31 during
which measurements are taken.
As pressure in cuff 10 decreases, flow through the brachial artery will
commence and a detection signal Vd will start to appear. At the
commencement of the detection signal Vd, an input of this signal to
controller 32 causes motor 30 to operate at a slower constant speed to
enhance measurement accuracy in the regions of systolic and diastolic
pressures, as suggested in U.S. Pat. No. 3,814,083. When the reverse
stroke of pump 28 is complete, after measurements have been taken and
recorded, the drive shaft 31 of pump 28 automatically trips a lower limit
switch 38 to cause controller 32 to stop motor 30. As can be seen from the
foregoing description of operation, the blood pressure measurement system
of the present invention provides automatic cycling through the full
measurement process in a simple manner using easily generated inputs to a
controller which is required to change only the speed and direction of an
electric motor to obtain the desired control.
As illustrated in FIG. 1, the cuff 10 and pressure source 26 are
pneumatically coupled by means of conduit 24 to a ballast tank 40. Due to
variatons in the circumferences of patient's arms, a convenional cuff of
fixed dimensions is incapable of covering all arm circumferences. Six
sizes of cuffs typically are required to accommodate all arm sizes, and
each cuff requires a different volume of air in order to reach the
required pressure for the underlying brachial artery to be occluded. To
retain a constant air volume with all six cuffs and a single fixed volume
pump 28, ballast tank 40 is provided. By varying the position of a manual
control shaft 42, the internal volume 43 of ballast tank 40 is adjusted to
complement the volume of a particular cuff 10 and to thereby obtain a
constant volume for pump 28 to inflate. As shown in FIG. 1, the ballast
tank 40 includes a diaphragm 44 coupled to control shaft 42 through a
spring 46. By varying the control shaft 42, spring pressure is brought to
bear on diaphragm 44 to adjust the internal volume 43 of the tank.
Preferably, for ease of adjustment, the control shaft 42 is arranged with
a plurality of settings each corresponding to a particular cuff size.
The linearly varying pressure in cuff 10 is applied, in conjunction with
detection signal Vd, to a recording apparatus 50 arranged to generate an
oscillatory record 52 of the detected arterial flow variations on
calibrated chart 18. As illustrated in FIG. 1, cuff 10 is pneumatically
coupled by conduit 24 to a pneumatic recording actuator 54 which, as will
be described in greater detail below with reference to FIGS. 5-7, is
arranged to translate the cuff pressure into a corresponding lengthwise
mechanical displacement of an output shaft 56. An arm 58, pivoted at 60,
is linked to shaft 56 and rotated thereby. The arm 58 mounts a radially
movable recording pen 62 above chart 18. A dynamic pen driver 64, carried
by arm 58, receives the detection signal Vd through the contacts of a
relay circuit 66 and drives the recording pen 62 in a radial direction in
proportion to the detection signal.
The recording apparatus 50 operates in the following manner: As pump 28
inflates cuff 10, arm 58 swings the pen 62 across chart 18. Because no
record is to be made during inflation of the cuff, relay circuit 66 is
arranged to have its contacts open during this time to prevent a signal
from being applied to pen driver 64. When the upper limit switch 36 is
actuated to reverse the pump motor 30, the contacts of relay circuits 66
are closed in response thereto.
As pump 28 linearly deflates cuff 10, arm 58 pivots steadily across chart
18. Calibration lines 68 on chart 18 indicate in appropriate units (e.g.,
mm. Hg) the cuff pressures corresponding to the various positions of arm
58 thereover. As detection signals Vd are received through the closed
contacts of relay circuit 66, pen driver 64 responds by moving recording
pen 62 radially back and forth to provide an oscillating trace 52 of the
detected flow variations in a permanent form on chart 18. Through the use
of calibration lines 68, the chart 18 will show at what cuff pressures the
various arterial flow variations have taken place. When cuff 10 is fully
deflated and pump 28 actuates the lower limit switch 38, the contacts of
relay circuit 66 are again opened in preparation for a subsequent cycle of
operation.
In addition to the record of arterial flow variation versus cuff pressure
provided on chart 18, the blood pressure measuring system of the present
invention is arranged to provide an accurate measurement and record of the
systolic and diastolic pressures of the arterial vessel. A precise
indication of the systolic and diastolic pressues is provided by a signal
analyzer 70 receiving the detection signal Vd and preferably having the
circuit arrangement described in U.S. Pat. No. 3,814,083, incorporated
herein by reference.
Briefly, such a signal analyzer 70 operates by processing detected Korotkov
sounds and utilizes a microphone 12 having a flat frequency response over
the range of 10-100 Hz. The amplified microphone output Vd is supplied to
a systolic Korotkov sound detecting system comprised to two channels. One
channel of the system has a bandpass filter 72 having a range from 18 to
26 Hz. These signals in the bandpass range are passed to an absolute value
circuit 74 which provides output signals representative of the absolute
values of the filtered input signal. The signals from the absolute value
circuit 74 are passed to a comparison circuit or comparator 76.
The other channel of the systolic Korotkov sound detecting system includes
an absolute value circuit 78 which provides absolute value signals to a
circuit 80 which detects peak values and holds the maximum peak value
detected. The output of the peak detector 80 is also supplied to the
comparison circuit 76. The comparison circuit is constructed and arranged
to consider the output of circuit 74 as a numerator value and the output
of circuit 80 as a denominator and produce an output signal dependent on
the ratio value of the two input values. The comparison circuit is further
arranged to produce a positive voltage output signal only when the ratio
value is equal to or greater than 0.45. The comparator may be a standard
commercial item such at the National Semiconductor LM 311 which is
conventionally used as an amplifier with two operational states. Whenever
the ratio is less than 0.45, the amplifier output is negative or zero;
otherwise it saturates at full scale positive.
The processor circuitry also includes a channel for diastolic Korotkov
sound detection. This channel includes a bandpass filter 82 having a
frequency range from 40 to 60 Hz. The output of the filter 82 is supplied
to an absolute value circuit 84 which provides absolute value output
signals. The signals from circuit 84 are supplied directly to a comparison
circuit or comparator 86 and to a circuit 88 which detects peak values and
holds the maximum peak value detected. The output of the peak detector 88
is supplied to the comparison circuit 86. Comparison circuit 86 receives
the detector output 88 as a denominator value and the absolute value
signal as a numerator and provided an output signal when the ratio value
falls below a value of 0.17.
The output signals from comparator 76 and comparator 86 are supplied to an
OR gate 90, the output of which will be signals occurring at the systolic
and diastolic events. The systolic and diastolic signals are applied to
pen driver 64 in recording apparatus 50, preferably at a higher signal
level than the detection signal Vd, so as to provide higher amplitude
traces 92, 94 on chart 18 which are distinguishable form the flow
variation trace 52. Thus there is automatically and permanently provided
on chart 18 both a continuous record of arterial flow variations versus
pressure and an accurate record of detected systolic and diastolic
pressures.
The systolic and diastolic pressures also may be recorded temporarily if
desired on the display 20, which preferably is of the digital variety
showing the detected values in alphanumeric characters. To obtain such a
display, the systolic and diastolic signals from analyzer 70 may be
supplied to control the operation of a gate circuit 96. When the gate
circuit 96 receives either the systolic or diastolic signals, the gate
circuit is arranged to pass along to display 20 a pressure signal Vp which
is proportional to cuff pressure values for the time that the gate is
operated. In accordance with the present invention, the cuff pressure
signal Vp is automatically generated by the operation of pneumatic
recording actuator 54. As shown in FIG. 1, the output shaft 56 of actuator
54, which is displaced linearly in relation to cuff pressure, carries a
contact element 98 which varies the characteristics of an electrical
device such as a resistance 100. The pressure signal Vp may be derived
from the varying resistance 100, e.g., by means of the illustrated voltage
divider arrangement employing a voltage source 102 in series with the
resistance 100.
Still another form of useful diagnostic information may be provided by the
blood pressure system of the present invention. By using a microphone 12
with a wide frequency response, such as from 5 to 5000 Hz., and a wideband
audio amplifier circuit 104, the loudspeaker 22 will provide not only the
fundamental wave or pulse, but also all harmonics and overtones, making it
possible to hear a murmur and the tone character of the murmur. Such a
high fidelity representation of arterial flow variations in aural form is
useful for diagnostic purposes and is readily provided in the present
system as a concomitant to the previously described measurement and
recording functions.
The blood pressure measuring system of the present invention thus provides
a versatile array of useful records and information on chart 18, display
20, and loudspeaker 22. If desired, various switches (not shown) may be
provided to obtain such records and information either independently or
simultaneously.
Turning again to pressure source 26, FIGS. 2-4 illustrate in detail a
preferred embodiment of the construction thereof. Pump 28 comprises a base
110 mounting an integral cylindrical housing portion 112 having a flange
112f joined to the flange 114f of a second cylindrical housing portion 114
by fasteners 116. Within the cylindrical inner space formed by mating
housing portions 112, 114 is a piston 118 secured to drive shaft 31 by
fastener 119. The piston 118 is coupled to cylinder portions 112, 114 by a
foldable cylindrical sleeve membrane or diaphragm 120, made for example of
rubber, and attached to one end to piston 118 by means of a retainer plate
122 and fastener 119, and attached at the other end between housing
flanges 112f, 114f. An end wall 124 of cylindrical housing portion 114
contains an umbrella relief valve 126 and an outlet connector 128 joining
to conduit 24. The end wall 124, housing portion 114, and diaphragm 120
form a contained interior chamber or air space 130 in pump 28 which is
variable in volum by movement of piston 118 to cause the inflation and
deflation of cuff 10. The diaphragm 120 folds over itself as the piston
118 moves and thereby maintains a leakage free seal between piston 118 and
cylindrical housing 112, 114 for reliable, repeatable pressure changes.
When the cuff is fully deflated, and piston 118 is near the right end (as
seen in FIG. 3) of the housing, the pressure in the contained space 130 is
essentially the ambient pressure and there is no pressure loading of
diaphragm 120. Without any loading, the folded diaphragm 120 tends to slip
along the interior surface of the housing as the piston starts its forward
stroke (toward the left in FIG. 3), which may result in jamming of the
diaphragm or nonlinear pressure changes if subsequent loading causes the
diaphragm to slip back. To avoid such undesired slippage when starting the
pump on its forward stroke, the interior surface of housing portion 112 is
provided with a frictional lining 132 to grip the diaphragm 120. The
frictional lining preferably is formed with an abrasive, as provided for
example by sandpaper grit, or is formed with a tacky substance.
As shown in FIG. 3, the piston drive shaft 31 is journalled through a hub
133 in end wall 134 of housing portion 112 and is threaded. A gear 136
threadably engages shaft 31 and is fixed against axial travel by end wall
134 and a retaining plate 138. The gear 136 is rotated by a meshing pinion
140 rotatably driven by pump motor 30 to thereby move drive shaft 31
axially in a forward, inflating stroke or in a reverse, deflating stroke
as required by controller 32. From the foregoing description it can be
seen that pump motor 30, when operated at a constant speed, will cause
linear movement of piston 118 and a linear, positively controlled buildup
or decrease of pressure in cuff 10. As it is a simple matter to operate
motor 30 at a constant preselected speed, the pressure source 26 of the
present invention provides a simple and uncomplicated device for achieving
linear and repeatable rates of pressure decrease in cuff 10 for accurate
blood pressure measurements.
As illustrated in FIGS. 2-4, the piston drive shaft 31 carries near its end
a transverse pin 142 which rides in a slot 144 in base 110 to prevent
rotation of shaft 31. In addition, as it travels lengthwise with shaft 31,
the pin 142 is arranged to trip actuators 36a and 38a of the upper and
lower limit switches 36 and 38, mounted on base 110 in positions
corresponding to the maximum forward and reverse positions of piston 118.
Accordingly, the pump 28 is readily and easily adapted to provide signals
at the maximum and minimum cuff pressures for automatic control of the
pump through motor speed controller 32.
The construction of pressure source 26 is such that base 110, housing
portions 112, 114 and piston 118 may be made of injection molded plastic,
for economical construction.
FIGS. 5-7 illustrate in greater detail the construction of the preferred
embodiment of the recording actuator 54 of FIG. 1. As shown in FIGS. 5-7,
the actuator 54 comprisescylindrical mating housing portions 146, 148
having flanges 146f, 148f joined by fasteners 150. An inlet connector 152
admits pressurized air from cuff 10 through conduit 24 to a contained
space formed by a piston 154, a foldable sleeve diaphragm 156, and housing
portion 146. Changing pressure in the space moves piston 154 against the
resistance of a spring 158 to displace actuator shaft 56, joined to piston
154, in an axial direction. By making the resistance of spring 158
proportional to pressure, displacement of actuator shaft 56 will be
linearly related to the pressure in cuff 10. Adjustment screws 157 bearing
on spring retainer 159 permit adjustment of the position of shaft 56 and
calibration of recording apparatus 50.
Secured to actuator shaft 56 is a member 160 providing a coupler 162 for
attachment to the pivotable recording arm 58. Member 160 also carries a
wiper 164 functioning as the electrical contact 98 of FIG. 1. A platform
166 on housing portion 148 carries resistance strip 100 in contact with
the wiper 164, and a parallel conductive jumper strip 168 also is in
contact with wiper 164 so as to present at output terminals 170, 172 (FIG.
7) a resistance which varies linearly with the displacement of actuator
shaft 56 and thus linearly with the pressure in cuff 10.
FIG. 8 illustrates in greater detail the construction of pump motor speed
controller 32 of FIG. 1. As shown in FIG. 8, controller 32 comprises a
regulator circuit 180 and a relay circuit 182 connected to pump motor 30,
to switches 16, 34, 36 and 38, and to a line carrying the detection signal
Vd. The motor 30 is a DC voltage sensitive type which produces at its
terminals 184, 186 a counter EMF in direct ratio to its rotational speed
(R.P.M.), and which thus is controllable by regulating its input power to
obtain a prescribed counter EMF.
Regulation of the speed of motor 30 is provided by regulator circuit 180,
which comprises a regulator 188, for example a model LM-117 made by
National Corporation, having a power input terminal Ti, a power output
terminal To, and a control terminal Tc to which a control voltage is
applied. In conventional regulator fashion, the regulator 188 has
terminals To and Tc connected to motor terminals 184, 186 and adjusts the
power supplied to the motor 30 to maintain its counter EMF equal to the
control voltage applied at regulator control terminal Tc.
The control voltage at terminal Tc, and thus the speed of pump motor 30, is
set by a switchable voltage divider circuit comprising resistors R1
through R4 and transistor switches Q1 and Q2. Capacitors C1 and C2 are
provided to damp switching transients. As shown in FIG. 8, the regulator
circuit 180 permits the pump motor to be operated at different constant
speeds by applying, at suitable times, different control voltages at
regulator control terminal Tc. When a cycle of operation is started,
transistor switches Q1 and Q2 are open, and closure of start switch 16
applies a source of voltage Vs to regulator input Ti and to the series
circuit formed by resistors R1 and R2. The voltage across resistor R2
appears at regulator control terminal Tc and the regulator 188 establishes
a corresponding rate of motor speed to provide the desired inflation rate
in cuff 10. Upon actuation of the upper limit switch 36 (when the cuff 10
is fully inflated), relay circuit 182 causes transistor Q1 to conduct,
thereby placing resistor R3 in parallel with resistor R2, lowering the
control voltage at terminal Tc, and reducing the speed of motor 30 to a
second constant rate. When microphone 12 produces a detection signal Vd,
transistor Q2 is caused to become conductive, thereby placing resistor R4
in parallel with resistors R2 and R3, and further lowering the control
voltage and motor speed to a third constant rate selected to provide
increased accuracy of detection of systolic and diastolic rates. It will
be apparent that proper selection of the values of resistors R1 through R4
will permit predetermined constant rates of inflation and deflation to be
achieved.
Relay circuit 182 governs motor 30 and regulator circuit 180 through a
cycle of operation by means of a relay 190 having contacts K1 through K4
illustrated in the state each assumes when the relay 190 is deenergized.
As will be explained below from a description of the relay's control
features, the relay 182 remains deenergized during the inflation stroke of
pump 28, becomes energized in response to actuation of the upper limit
switch 36, and remains energized during the deflation stroke.
Relay contacts K1 and K2, as shown in FIG. 8, are connected between motor
30 and regulator 188 to reverse the polarity of voltage applied to motor
30 at the end of the inflation stroke of the pump and to cause the motor
to reverse its direction and perform the deflation stroke. Contact K3 is
arranged to connect a voltage, derived for example from the voltage
divider formed by resistors R5, R6 and voltage source Vs, to the base of
transistor switch Q1 to cause it to conduct and thereby effect a change in
motor speed. Contact K4 is provided to hold relay 190 energized during the
deflation stroke.
Control of the motor speed controller 32 through a cycle of operation is
effected by switches 16, 34, 36 and 38. The voltage source Vs is connected
to regulator circuit 180 through | | |
