U.S. patent number 3,675,243 [Application Number 05/004,967] was granted by the patent office on 1972-07-04 for electronic drip timing device.
This patent grant is currently assigned to Illinois Tool Works Inc.. Invention is credited to John F. Landuyt.
United States Patent |
3,675,243 |
Landuyt |
July 4, 1972 |
ELECTRONIC DRIP TIMING DEVICE
Abstract
Electronic timing device for timing drips in intravenous feeding
and similar systems can be adjusted to provide an audible or
visible signal in accordance with any desired drip rate between
about 4 and 300 drips per minute. The device overcomes the inherent
deficiency of conventional electronic metronomes which are
unsuitable for adjusting drip rates since they have a first pulse
period different from the remainder. The first pulse period is of
the exact length of the remaining pulse periods due to the presence
of a circuit which can be maintained in a standby condition with
its capacitor partially charged. This permits the pulse producing
circuit to be actuated simultaneously with the visual observance by
an operator of a drip passing a predetermined point. If the actual
drop rate is different from the desired rate, the operator adjusts
it and again actuates the timing device. This operation is repeated
until the timing rate and the drip rate are synchronized. The
device is battery operated and sufficiently small as to be easily
carried around the neck or in the pocket of the person using
it.
Inventors: |
Landuyt; John F. (Des Plaines,
IL) |
Assignee: |
Illinois Tool Works Inc.
(Chicago, IL)
|
Family
ID: |
21713445 |
Appl.
No.: |
05/004,967 |
Filed: |
January 22, 1970 |
Current U.S.
Class: |
340/384.71;
331/153; 968/818; 84/484; 968/820 |
Current CPC
Class: |
G04F
5/02 (20130101); G04F 5/025 (20130101); A61M
5/1689 (20130101); A61M 2209/02 (20130101) |
Current International
Class: |
A61M
5/168 (20060101); G04F 5/00 (20060101); G04F
5/02 (20060101); G08b 003/00 (); H03k 003/31 () |
Field of
Search: |
;331/111,131,143,153,149,145 ;328/66 ;340/384E ;307/271,301,252
;84/484 ;58/130 ;324/186 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
J V. Crowling, "Modified UJT Oscillator," EEE-Circuit Design
Engineering, Dec. 1966, pp. 120-121..
|
Primary Examiner: Griffin; Robert L.
Assistant Examiner: Martin; John C.
Claims
I claim:
1. A device for producing a plurality of pulses having a period
between pulses of a selected predetermined length comprising a
relaxation oscillator circuit including a capacitor and a plurality
of resistance members in series in a signalling means which have a
time period of a predetermined length in accordance with the
equation:
t = RC 1n V.sub.B - V.sub.o /V.sub.B - V.sub.c
where:
t = time
R = series resistance
C = capacitance
V.sub.B = battery voltage
V.sub.C = capacitor voltage
V.sub.o = initial capacitor voltage primary switch means for
connecting the battery to close said oscillator circuit;
reset resistance means and reset switch means operable for
selectively connecting said reset resistance means in said closed
circuit in parallel connection with said capacitor and shunting one
of said plurality of resistance members which has a greater value
of resistance, said reset resistance means having a resistance
value sufficiently low to prevent said circuit from oscillating to
produce pulses while maintaining the voltage across the capacitor
at a constant value equal to the value V.sub.o which it has when
the reset switch is open and the circuit is oscillating to produce
pulses.
2. The device as described in claim 1 wherein said reset switch
means is operative when actuated in one mode to connect said reset
resistance in said circuit in parallel connection with said
capacitor and to remove said one of said plurality of resistance
members from series connection with said capacitor, said switch
being operative when actuated in another mode to remove said reset
resistance from said circuit and to restore said one of said
plurality of resistance members to series connection with said
capacitor.
3. The device as described in claim 2 wherein said one of said
plurality of resistance members comprises variable resistance means
for varying the value of the series resistance R and thus the time
t in said equation.
4. The device as described in claim 2 wherein said reset switch
means comprises a momentary switch having a spring biased actuator
witch is depressed to be actuated in said one mode and released to
be actuated in said other mode.
5. The device of claim 3 wherein said primary switch means and said
variable resistance means are operatively interconnected for
actuation by a common control member.
6. The device of claim 1 wherein said signalling means includes a
speaker for producing an audible sound.
7. The device of claim 2 wherein said oscillator circuit includes a
transistor connected in fixed parallel relation to said capacitor
and operative to trigger the discharge of said capacitor only when
said reset switch is in said other mode and said transistor and
capacitor are at a predetermined voltage in excess of said
capacitor voltage V.
8. The device of claim 7 wherein a speaker is connected in series
with said transistor, said capacitor being in parallel with said
series connected transistor and speaker, said speaker producing an
audible sound pulse when said capacitor discharges through said
transistor.
Description
BACKGROUND OF THE INVENTION
This invention relates to timing devices and particularly to timing
devices used to adjust the rate of flow of fluid to a patient such
as in blood transfusions or intravenous feeding. Although there are
fairly sophisticated devices known in the prior art for
automatically regulating the flow of fluid or for indicating the
rate of flow, such devices would be almost prohibitively expensive
to use since a complete device would have to be provided at each
location where fluids were being fed. It is the usual practice in
the vast majority of hospitals for the drip rate to be adjusted by
a doctor or a nurse who uses a stop watch to time the drip rate.
Since different fluids being administered require different drip
rates varying over a substantial range such as from 4 to 300 drips
per minute, one can readily appreciate that it would be physically
impossible to count very high drip rates and very time consuming to
count and adjust low drip rates.
Since the drip rate range is generally within the range of timing
pulses produced by electronic metronomes, one might think that such
a device could be used to aid in the determination of drip rates.
However, certain problems are presented depending on which type of
metronome is used. For example, in a metronome or beat producing
device such as shown in U.S. Pat. No. 3,271,670, a single rotatably
adjustable control member is used to turn on the device and then
set the frequency to a desired rate. Obviously, such a device could
not be operated to produce a pulse period starting with a
particular drip and thus, in order to time the drip rate one would
have to set the metronome to the desired rate and then observe the
exact position of a drip relative to the walls of a drip tube which
contains it at the time of a pulse and then observe whether or not
the next drip is above or below the point where the first one was
observed at a time when the next pulse or beat is heard. Obviously,
such a metronome could only be used with very high drip rates
and/or long drip tubes to insure that a drip would be in motion in
the tube at all times. For lower drip rates, the device would have
to be continually set and reset until a drip was visible at the
time of a pulse. The setting and resetting would have to be
continually repeated until the actual drip rate was correctly
adjusted.
Other electronic metronome devices, such as, for example, the
device such as in U.S. Pat. No. 2,522,492, utilize separate
controls for setting the beat rate and for turning the device on
and off. Theoretically, it would seem that such a device could be
used for timing drip rates since a user could set the metronome to
beat at a rate equal to the required drip rate and then simply turn
the device on when the drip is observed at a particular location
such as the bottom of the drip tube. It has been found, however,
that such a proposed method of operation of a metronome as a drip
timer is not suitable since the very nature of electronic pulse
producing circuits provides for a first pulse which is of longer
duration than the remaining pulses. For the usual use of a
metronome, this is of no particular importance since the device is
merely used to provide a continuing beat of a desired frequency. In
order, however, to utilize an electronic metronome or pulse
producing device as a drip timer, it would appear to be desirable
to be able to set the beat rate and then keep the device from
pulsing or beating until a drop is observed hitting or passing a
given point. Such operation would result in easier synchronization
and determination of the correct rate. Obviously, if such a means
of determining drip rates is to be useful, the first pulse period
is very important and has to have the same duration as the
remainder.
Electronic metronomes commonly include a resistance-capacitance
network wherein the capacitor is alternately charged and discharged
to provide a series of pulses. The time to charge the capacitor in
such a circuit (the factor determining the duration of a pulse
period) can be found from the following equation:
t = RC 1n V.sub.B - V.sub.o /V.sub.B - V.sub.c
wherein:
t = time
R = series resistance
C = capacitance
V.sub.B = battery voltage
V.sub.C = capacitor voltage just prior to discharge
V.sub.o = initial capacitor voltage
It can be readily seen from the equation that the first pulse
period will be longer than the remaining ones when the circuit is
turned on since the capacitor has to start charging from an initial
voltage, V.sub.o = o rather than the higher initial voltage which
it would have at the beginning of each following time period. It is
thus apparent that trying to start synchronization with the
capacitor at zero volts, such as would be the case if the capacitor
were shorted out or the circuit closed by an on-off switch, would
be unsatisfactory and would result in the first time interval being
too long and thus providing a mismatch between drops and beats.
SUMMARY
Among the objects of this invention are to provide a simple,
effective, economical, and compact device for aiding a nurse or
other person in quickly and accurately adjusting the drip rate of a
fluid feeding apparatus.
These and other objects are obtained by the present invention. In
the preferred embodiment of the invention, the various elements are
housed in a small case which can be easily supported by a cord
placed around the neck of the nurse. The device includes a
combination on-off and rate setting switch which connects an
enclosed battery to a relaxation oscillator circuit, and also
adjusts the circuit to change the beat rate of the device. The
output of the device is preferably audible in which case the sound
is heard from a speaker enclosed in the device, or by means of an
ear plug. Alternatively, a visual signal such as a light could be
used to provide a silent signal.
The basic operation of the circuit in the device is that when the
on-off switch is turned on, a capacitor which is in parallel with a
series connected transistor and speaker coil is subjected to a
voltage across its terminals and initially resembles a short
circuit. The voltage across the capacitor immediately starts to
build up until it reaches the trigger voltage of the initially
non-conducting transistor in parallel with it. At this point, the
transistor becomes conductive and causes the capacitor to be
discharged through the speaker. This cycle of alternate charging
and discharging of the capacitor will then be repeated continually.
The time period for charging and discharging the capacitor, and
thus the time between pulses, can be varied by changing the
resistance value in the R-C network. Obviously, when the R-C value
is increased, it will take a longer time for the capacitor to
charge and the beat rate will be slower. Conversely, decreasing the
R-C value will cause the capacitor to discharge sooner and thus
have a higher beat frequency. The voltage at which the capacitor
will discharge, its trigger voltage, is determined by a plurality
of resistors connected in series in a voltage divider network to a
transistor. A compensating resistor and a blocking diode in the
circuit provide a temperature compensation network.
A normally open switch adapted to be closed by a spring loaded
reset button on the outside of the case or housing permits a fixed,
low value resistance to be selectively placed in the circuit in
parallel with the capacitor. The reset switch also electrically
removes the relatively high value variable resistance used for
changing the beat rate from the circuit. With the reset switch
actuated, the reset resistance and the capacitor are each connected
in series with a fixed resistance. The effect of the low value
resistance which is inserted by the reset switch is to cause the
capacitor to be charged to a voltage greater than zero and equal to
the voltage which it assumes during normal operation of the device
at the beginning of each charging cycle. A normal operating
sequence would be to turn the device on, set the rate, (beats will
be produced) and then hold the circuit in a partially "on"
condition but one wherein no pulses are produced by means of the
reset button. The reset button is released when the operator
visually observes a drip hitting the bottom of a drip tube or some
other point in a fluid dripping device such as an intravenous
feeding apparatus. If the next drip observed comes either sooner or
later than the first pulse or beat produced by the device, then the
flow rate of the feeding apparatus is adjusted appropriately and
the reset button is again held in until it is released when a drip
is observed. This sequence of operations is then repeated until the
actual drip rate corresponds to the desired drip rate.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic perspective view of a drip timing device
in accordance with the invention;
FIG. 2 is a graph showing capacitor voltage versus time for a
capacitor in a prior art pulse producing relaxation oscillator
circuit; and
FIG. 3 is a circuit diagram of the electronic circuit of the
device.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows the drip timing device of the invention indicated
generally at 10 and including case 11 comprising a pair of case
halves 12, 14 held together by a fastener member 16. The device can
readily be stored in the pocket of an operator or may be hung
around the operator's neck by means of a pair of integral lug
members 18 about which a carrying cord 20 may be attached. At one
end of the device 10, a dial 22 is provided which includes a
plurality of indicia thereon corresponding to the varying beat
rates from 4-300 beats per minute which may be produced. A rotary
knob 24 having a pointer 26 overlies the dial 22 and is attached to
an on-off switch S.sub.P and a variable resistance R.sub.2 (FIG. 3)
mounted inside the case for turning the device on and off and
setting the pulse or beat rate to any value throughout the range of
4-300 beats per minute. The audible signal produced by the device
can be heard either through speaker openings 28 or by means of an
ear phone (not shown) which may be connected to the device by means
of jack 30. A reset button 32 on the side of the case 11 is adapted
to be depressed against the force of a spring (not shown) to
operate a reset switch S.sub.R and hold the circuit of the device
in a partially "on" or standby condition as will be described more
fully hereinafter.
In FIG. 2, a graph of capacitor voltage versus time is plotted for
a capacitor in a known relaxation oscillator circuit. Referring to
the graph, one can see that the capacitor in the circuit will
alternately charge and discharge and that initially the capacitor
will build up a charge from an initial capacitor voltage equal to
zero to a final voltage V.sub.C which is the capacitor voltage at
the instant prior to discharge. This increase in capacitor voltage
with time as the circuit is first closed is illustrated by curve 40
while curve 48 represents the fall-off in voltage from value
V.sub.C to a value V.sub.o, which is greater than zero, at the
completion of discharge. The exact values of V.sub.o and V.sub.C
depend upon the values of the various resistances in the circuit.
After the first capacitor charging period represented by the curve
40, each remaining charging period can be presented by identical
curves 42, 44 and 46 and each discharge period by identical curves
50, 52 and 54. Identical time periods T.sub.2, T.sub.3 and T.sub.4
are of a duration equal to the total time required for the
capacitor to charge and discharge (the horizontal components of the
charging and discharging curves 42, 50 respectively). It will be
readily appreciated that the time period T.sub.1 corresponding to
the first charging curve 40 and the discharge curve 48 will be
longer than the remaining time periods T.sub.2, T.sub.3 and T.sub.4
by the amount of time necessary for the capacitor to charge when
turned on from a voltage value equal to zero to a voltage value
equal to V.sub.o.
Since it is necessary, in order for a pulse producing device to be
useful in adjusting drip rates for the first time period T.sub.1 to
be equal in length to the remaining periods T.sub.2, T.sub.3 .....
T.sub.N, the time period T.sub.1 must be shortened. This can be
accomplished by the circuit shown in FIG. 3 which permits the
length of charging curve 40 to be shortened by an amount equal to
the length of curve 56 between voltage V.sub.o = o and the value of
V.sub.o which is greater than zero which is indicated by the lower
dotted line in FIG. 2.
Referring to the circuit diagram of FIG. 3, a battery indicated
generally at 34 having a voltage of 4.2 volts is connected between
ground and a primary on-off switch S.sub.P which opens and closes
the battery circuit and connects the battery 34 by means of wires
60 to a common terminal point 62 connected to a resistance R.sub.1
having a value of 5.6K and a parallel connected resistance R.sub.3
having a value of 1K. Connected in series with resistance R.sub.3
are two more resistances, R.sub.4 having a value of 2K, and R.sub.5
having a value of 10K which form a voltage dividing network.
Resistance R.sub.4 is a trimmer resistance which is tapped at a
point 64 along its length by a blocking diode 66 which may be of
the type sold by General Electric Co. under the number 1N 4154. The
diode 66 is in series with a resistance R.sub.6 having a resistance
of 1 meg and coacts with resistance R.sub.6 to form a temperature
compensation network. The diode 66 is also connected to the gate G
of a transistor 70 of a type sold by General Electric Co. under the
number D 13T1 which has its cathode K connected to ground through
the coil 72 of a 3.2 ohm speaker 74.
The 5.6K resistance R.sub.1 is connected in series with a variable
resistance R.sub.2 having a maximum value of 420K which in turn is
connected to the anode A of the transistor 70. The variable
resistance R.sub.2 provides the variation in beat rate of the
circuit and is adjustable by means of the knob 24. The basic
relaxation oscillator circuit is completed by a capacitor C having
a value of 22 mfd which is connected in parallel with transistor 70
and speaker coil 72 between the junction of resistors R.sub.1 and
R.sub.2 and ground.
The circuit as described to this point is known and will produce
pulses or beats having a time for the first pulse longer than the
time for the remaining pulses as described in connection with the
graph in FIG. 2.
The remainder of the circuit to be described is the portion which
permits the time period of the first pulse to be equal to the time
period of the remaining pulses and includes the resistance R.sub.7
having a value of 1.2K and the reset switch S.sub.R which has a
first set of contacts 80 which can be closed to place the
resistance R.sub.7 in series with the resistance R.sub.1 and in
parallel with the capacitor C. A second set of contacts 82 on the
reset switch S.sub.R electrically removes the large variable
resistance R.sub.2 from the circuit and connects resistance R.sub.1
directly to the transistor 70 and capacitor C. Since the resistance
R.sub.7 has a value 1.2K which is approximately 20 percent of the
value of the 5.6K resistance R.sub.1, it is readily apparent that
the voltage across the capacitance C will be approximately 20
percent of the 4.2 volt battery voltage or approximately 0.9 volts.
Since this value is less than the trigger voltage of the transistor
70 which has a value of approximately 3.4 volts, it is obvious that
the capacitor C cannot discharge through the transistor 70 and will
retain its charge as long as the switch S.sub.P is closed and the
reset switch S.sub.R is depressed by finger pressure on the reset
push button 32. Since the values of the various resistances are
chosen to cause the capacitor C to be charged to a voltage which is
equal to the value V.sub.o on the lower dotted line in FIG. 2, it
will be readily apparent that releasing the reset switch S.sub.R,
such as when a drip is observed in an intravenous feeding
apparatus, will result in a first pulse having a duration of time
equal to that of the remaining pulses which will be produced after
the reset switch S.sub.R is released.
The resistance R.sub.1 determines the shortest time period between
pulses which the device can produce. In the present device, this
shortest time period is 300 pulses per minute. The point 64 at
which the blocking diode 66 is tapped into the trimming resistor
R.sub.4 determines the trigger voltage of the transistor 70 which
in the present embodiment is approximately 3.4 volts. Once the
trimming resistor R.sub.4 is initially adjusted, to the remaining
circuit components to provide an accurate beat rate, no further
adjustment should be necessary in order to maintain the accuracy of
the pulse rate produced by the device as long as the battery 34 is
in good condition.
Although a speaker 74 has been shown as a means of rendering the
discharge of capacitor C audible, it is obvious that an earphone
could be substituted for the speaker coil 74 if the device were to
be used in a relatively noisy room or if it were desired that
patients not be awakened. For this purpose, an earphone can be
inserted into the circuit by means of jack 30 shown in FIG. 1.
Alternatively, a visual signal such as a flashing light could
signal the beat rate if appropriate changes were made in the values
of the various elements of the circuit.
* * * * *