U.S. patent number 3,729,729 [Application Number 05/178,244] was granted by the patent office on 1973-04-24 for annunciator system.
Invention is credited to Martin R. Geller, David A. Goldman.
United States Patent |
3,729,729 |
Geller , et al. |
April 24, 1973 |
ANNUNCIATOR SYSTEM
Abstract
An annunciator system of the type having a central annunciating
station and remote receptacles typically adapted for receipt of a
plug-in manual controller, not requiring power for operation
thereof, is improved by introduction of a controller adapted to
monitor changing conditions. The introduced controller is a plug-in
unit deriving all required operating power through the remote
receptacle and at the same time providing system control inputs
through the receptacle. The introduced controller may also have
facility for receiving the manual controller to provide the
annunciator system with plural inputs. units. In a preferred
arrangement, the system is shown in hospital usage where it
provides for the monitoring of a liquid level.
Inventors: |
Geller; Martin R. (New York,
NY), Goldman; David A. (Yorktown Heights, NY) |
Family
ID: |
22651788 |
Appl.
No.: |
05/178,244 |
Filed: |
September 7, 1971 |
Current U.S.
Class: |
340/538; 331/111;
331/65; 340/656; 340/620; 340/573.1 |
Current CPC
Class: |
A61M
5/1684 (20130101); G08B 25/00 (20130101); G01F
23/265 (20130101) |
Current International
Class: |
G08B
25/00 (20060101); A61M 5/168 (20060101); G01F
23/22 (20060101); G01F 23/26 (20060101); G08b
021/00 () |
Field of
Search: |
;340/244C |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Habecker; Thomas B.
Claims
What is claimed is:
1. An annunciator system comprising a central station including a
current source and annunciator means connected thereto and a remote
call station including a receptacle for connection to said
annunciator means and plug-in means matable with said remote
station receptacle, said plug-in means having a receptacle for call
means and further comprising: detecting means for detecting the
occurrence of a predetermined condition; signal generator means
responsive to said detecting means for generating an output signal
indicative of said condition occurrence; means conducting current
from exclusively said receptacle to both said detecting means and
said signal generator means for energization thereof; and control
means operatively responsive to said signal generator output signal
for controlling said current conducting means, thereby modifying
current flow through said annunciator means to selectively energize
said annunciator means to provide a sensible output upon the
occurrence of said condition.
2. The system claimed in claim 1 wherein said current conducting
means includes an impedance connected in series circuit with said
annunciator means and wherein said control means includes a switch
member connected in parallel with said impedance and operated by
said signal generator output signal.
3. The system claimed in claim 2 wherein said annunciator means is
energized upon current flow therethrough of magnitude higher than a
predetermined magnitude, said switch member being rendered
conductive by said signal generator output signal and thereby
increasing current flow to a magnitude higher than said
predetermined magnitude.
4. The system claimed in claim 2 wherein said annunciator means is
energized upon current flow therethrough of magnitude less than a
predetermined magnitude, said switch member being rendered
non-conductive by said signal generator output signal and thereby
decreasing said current flow to a magnitude less than said
predetermined magnitude.
5. The system claimed in claim 3 wherein said annunciator means
includes a visible indicator having a filament connected in series
circuit with said current source and said impedance.
6. The system claimed in claim 4 wherein said annunciator means
includes a visible indicator having a filament connected through
normally open contact means across said current source and further
includes contact closure means connected in series circuit with
said current source and said impedance.
7. The system claimed in claim 3 wherein said plug-in means
includes a receptacle section adapted for connecting manually
operable switch means in parallel with said impedance for
selectively energizing said annunciator means upon operator input
to said manually operable switch means.
8. The system claimed in claim 4 wherein said plug-in means
includes a receptacle section adapted for connecting manually
operable switch means in series circuit with said control means for
selectively energizing said annunciator means upon operator input
to said manually operable switch means.
9. The system claimed in claim 7 wherein said manually-operable
switch means includes a normally non-conductive switch element
rendered conductive by said operator input.
10. The system claimed in claim 8 wherein said switch means
includes a normally conductive switch element rendered
non-conductive by said operator input.
11. The system claimed in claim 1 wherein said condition detecting
apparatus includes an oscillator the frequency of oscillation of
which exhibits preselected change upon the occurrence of said
predetermined condition.
12. The system claimed in claim 11 wherein said predetermined
condition is the occurrence of a preselected liquid level, said
oscillator including a capacitance means having first and second
electrodes adapted for securement in opposing coplanar relation to
a dielectric vessel containing said liquid.
13. The system claimed in claim 12 wherein said capacitance means
includes a third electrode adapted for securement to said vessel in
non-coplanar relation to said first and second electrodes.
14. The system claimed in claim 8 wherein said signal generator
generates a periodic output signal.
15. The system claimed in claim 11 wherein said predetermined
condition is the occurrence of a preselected liquid level, said
oscillator including a capacitance means having first and second
electrodes adapted for securement to a dielectric vessel containing
said liquid and defining there-with first and second
series-connected capacitors, said vessel providing the dielectric
for said capacitors.
16. The system claimed in claim 15 including a third capacitor
comprising a third electrode and said liquid, said vessel providing
the dielectric for said third capacitor, said third capacitor being
connected to said first and second capacitors by said liquid.
17. Apparatus for use in an annunciator system having a central
annunciating station including a current source and annunciating
means and a remote receptacle connected to said station and adapted
for receipt of a plug-in member manually operable to provide a
control input to said annunciator system, said apparatus comprising
an adapter-connector insertable in said receptacle for connection
of said adapter-connector to said station and adapted for receipt
of said plug-in member, and circuit means connected by said
adapter-connector to said station, thereby deriving operating power
from said current source, for providing a further control input to
said annunciator system, said circuit means comprising detector
means for detecting the occurrence of a predetermined condition,
signal generator means operatively responsive to said detector
means for generating an output signal indicative of said condition
occurrence and control means operatively responsive to said signal
generator means for providing said further control input to said
annunciator system upon occurrence of said condition.
Description
FIELD OF THE INVENTION
This invention relates to annunciator systems and to improved
condition detector apparatus for use therein.
BACKGROUND OF THE INVENTION
The expansion of the capabilities of annunciator systems in
existing installations is of substantial current interest. For
instance, in presently constructed hospitals, the expansion of the
capabilities of the customary "patient call" annunciator system to
provide monitoring of various conditions, e.g., instantaneous
liquid levels in intravenous feeding and body fluid collection,
would provide evident advantages. Clearly, such additional
annunciating capabilities would afford opportunities for a
reduction in the number of personnel needed for customary periodic
condition monitoring and for increased security inherent in
continuous condition monitoring.
In the exemplary instance, i.e., expansion of the capabilities of
the hospital patient call system, various considerations affect the
practicality of expansion, and, if not satisfied, tend to overcome
the above-discussed advantages. Typically, the patient call system
comprises a central station having a current source and annunciator
panel and plural remote stations, each including a patient-operated
switch adapted to control current flow through its associated
central station annunciator. Accordingly, a seemingly expeditious
manner of system expansion is the provision of remote station
condition detector apparatus adapted to operate the patient switch
upon detection of a condition of predetermined interest and
deriving its operating current from conductors other than those
conducting annunciator controlling current. Such approach to system
expansion is, however, greatly impractical since it necessitates
elaborate mechanical apparatus for said patient switch operation
and separate conductors providing detector apparatus operating
current and does not enable central station discrimination as to
whether the patient or the detector apparatus is responsible for
the change in annunciator control current.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved
annunciator system integrally incorporating a pre-existing
annunciator system and expanding the annunciating capability
thereof.
It is a more particular object of this invention to provide a
hospital annunciator system combining at least an integral part of
a pre-existing patient call annunciator system with condition
detector apparatus deriving its operating current through such
pre-existing system.
It is a further object of this invention to provide improved
condition detector apparatus for use in the systems of the
invention.
In the efficient attainment of these and other objects, the
invention provides an annunciator system comprising a central
annunciating station and a remote station, the remote station
including a receptacle connected to the central station, and
connector-adapter means matable with the receptacle and
incorporating circuit means for both conveying annunciator control
signals to the central station and conducting operating current
from the central station through the receptacle to associated
remote station condition detecting apparatus. The connector-adapter
may further include the facility for receiving annunciator
controllers normally matable with the remote station receptacle
whereby the system is effective to provide annunciator control
signals upon the occurrence of a detected condition of interest
and/or another separate event.
In its preferred form, the system of the invention is adapted for
hospital usage and includes a pre-existing patient call annunciator
system having a central station and a remote station modified only
to the extent that a connector-adapter and associated circuitry for
condition detection and annunciator control is substituted for the
patient call plug at the remote station receptacle. In this
arrangement of the system, the condition detector is preferably
adapted for detection of a liquid level of interest and derives its
operating power through the remote station receptacle while
providing liquid level announcements through the pre-existing
annunciators. Where desired, the system may have the capacity for
concurrent distinct announcement of patient demands for attention
or the occurrence of a liquid level of interest.
The term "pre-existing," employed above and elsewhere herein to
describe systems which are improved by the invention, is intended
to embrace all systems whose annunciating capabilities are expanded
by the invention, irrespective of whether such systems pre-date the
invention.
In describing the manner in which the invention provides its
improved systems, we set forth examples of two such pre-existing
systems and indicate the improvements therein. These two systems
are not known to be precise renditions of presently known systems
but are believed to be representative of hospital annunciator
systems.
The foregoing and other objects and features of the invention will
be evident from the following detailed description of embodiments
thereof shown in the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the system of the invention.
FIGS. 2A and 2B illustrate types of annunciator units employable in
practicing the invention.
FIGS. 3A and 3B illustrate manually operable controllers employable
as secondary controller 16 in FIG. 1.
FIGS. 4A and 4B are schematic diagrams of controllers employable as
primary controller 48 in FIG. 1.
FIG. 5 is a schematic diagram of oscillator 54 and detector 58 of
FIG. 1.
FIGS. 6A and 6B are schematic diagrams of circuits employable as
voltage-sensitive switch 66 of FIG. 1.
FIG. 7 is a schematic diagram of an optional circuit adapted for
use in the FIG. 1 system to provide concurrent distinct system
announcements.
FIG. 8 illustrates a vessel for liquid containment and electrode
arrangements for use in detecting liquid levels of interest.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, an annunciator system comprises a central
station, typically the nurses' station on each floor of a hospital,
including a current source 10 and a plurality of annunciator units
12, and a plurality of remote stations, i.e., patient's bedsides,
each of which is associated with a one of annunciator units 12. In
systems preexisting the invention and in widespread use, a
receptacle 14 at the remote station is directly connected to the
central station and a plug-in controller 16 is matable with the
receptacle. In such systems, controller 16 may be of the type 16a
shown in FIG. 3A, incorporating a patient operable push-to-close
(PTC) switch 18a. In this instance, annunciator unit 12a (FIG. 2A)
is employed, comprising a lamp 20a series-connected in line 22.
Alternatively, the controller may be of type 16b (FIG. 3B)
incorporating a patient operable push-to-open (PTO) switch 18b. In
this instance, annunciator unit 12b (FIG. 2B) is employed,
comprising a lamp 20b connectable across lines 22 and 24 through
contact 26 and contact arm 28. Coil 30 is energized when switch 18b
is closed and contact arm 28 engages contact 32 as shown in the
drawings. In operation of such pre-existing systems, annunciator
unit 12 is energized upon the operation of switches 18a, 18b by a
patient, thereby providing indication at the nurses' station of his
need for attention.
In accordance with the present invention, such preexisting system
is modified by the introduction of a connector-adapter 38 (FIG. 1)
having a plug-in section matable with receptacle 14 and preferably
a receptacle section matable with unit 16. The customary direct
interconnection of patient switch 18 and its associated annunciator
unit 12 is interrupted by circuitry connectable to
connector-adapter 38. As illustrated, the plug-in section of unit
38 includes lines 40 and 42 respectively connectable with lines 34
and 36 and the receptacle section thereof may include lines 44 and
46 across which controller 16 may be connected. In this respect, it
should be understood that the subject invention pertains to the
illustrated system with controller 16 being optional and, to this
extent, controller 16 is referred to hereinafter as a secondary
controller. In use of the system of the invention with annunciator
units 12a, secondary controller 16 may be omitted without any
substitute connection to lines 44 and 46. Where annunciator units
12b are employed, in the absence of secondary controller 16 lines
44 and 46 may be interconnected by a jumper inserted into the
receptacle section of connector-adapter 38.
Lines 40-46 are connected to primary controller 48, variant forms
of which, 48a and 48b, are illustrated in FIGS. 4A and 4B
respectively for use in systems employing annunciator units 12a and
12b. As discussed in detail below, the primary controller
constitutes circuit means adapted both to provide control of
current flow through annunciator units 12 and, at the same time, to
conduct operating current to detector apparatus. The controller 48
is also connected to lines 50 and 52, line 50 being directly
connected to oscillator 54 and line 52 being connected to
oscillator line 55. Oscillator 54 may oscillate in relation to the
level of a liquid, e.g., a solution for intravenous feeding, and
accordingly provides an output signal on line 56 connected to
detector 58. The detector is connected to controller 48 by lines 50
and 60 and by lines 52 and 62. An output signal of preselected
amplitude is provided by detector 58 on line 64 upon the occurrence
of a liquid level of interest and is applied to voltage-sensitive
switch 66. This switch is connected to controller 48 by lines 50,
60 and 68 and by lines 52 and 70. Upon application of such
preselected signal to switch 66, the switch provides an output
signal on line 72 to primary controller 48. Controller 48 is
responsive to this signal to control current flow through
annunciator unit 12 to provide visible indication at the central
station of the occurrence of the liquid level of interest. Such
liquid level may be detected either in a liquid dispensing or
liquid collection mode as discussed below.
Where secondary controller 16 is employed in conjunction with
primary controller 48 and associated circuitry 50-72, primary
controller circuit structure permits continuing control of
annunciator unit 12 by the secondary controller. Thus, the
secondary controller may be operated, as in said pre-existing
systems, to provide central station annunciation of a patient's
demand for attention. Where desired, as discussed below in
connection with FIG. 7, the system of the invention permits
concurrent distinct indication of both such patient demand and the
occurrence of a liquid level of interest. In addition, controller
48 circuit structure provides that all operating current for itself
and units dependent thereon be derived from source 10 without need
for modification of the pre-existing system.
In the following detailed discussion of the structure and operation
of the systems of the invention, initial discussion is provided for
the system embodiment employing annunciator unit 12a, primary
controller 48a, secondary controller 16a (optional) and
voltage-sensitive switch 66a. The remaining elements of the system,
e.g., current source 10, oscillator 54 and detector 58, are the
same in each of the system embodiments.
In the first system embodiment of the invention, lamp 20a of
annunciator unit 12a is series-connected between lines 22 and 34,
lines 24 and 36 being directly interconnected. In such arrangement,
current of nominal amplitude may be drawn through lamp 20a without
exciting the lamp to provide a visible output. Applicants provide,
to advantage discussed below, that the operating current for liquid
level detection may readily be maintained below such nominal
amplitude, e.g., by use of low current drain circuitry, thereby
avoiding energization of lamp 20a during quiescent conditions,
namely, when either the liquid level of interest has not occurred
or when the patient is not in need of attention.
Referring to FIG. 4A, primary controller 48a may include a
rectifier 74 where current source 10 is an alternating current
source. The rectifier is connected to lines 40 and 42 and provides
its output on lines 76 and 78. Line 76 is directly connected to
line 46 of adapter-connector 38 and is connected through resistor
80 to connector-adapter line 44 through resistor 114. A Zener diode
82, or like device exhibiting a predetermined breakdown voltage is
connected between line 78 and resistor 80 and provides a
substantially constant direct current voltage across lines 50 and
52 which conduct operating current circuit to elements 54, 58 and
66 of FIG. 1. A voltage divider comprising resistors 84 and 86 is
connected between lines 76 and 72 for biasing the base of
transistor 88. The transistor emitter is directly connected to line
46 and the transistor collector is directly connected to the
junction of resistor 80 and diode 82. A local indicator for the
remote station, comprising a lamp 90 and diode 92, may be connected
across lines 50 and 72 where desired.
Referring to FIG. 5, oscillator 54 may be of conventional
structure, including transistors 94 and 96 and associated biasing
and operating components. The base of transistor 96 is directly
coupled to the collector of transistor 94 and the collector of
transistor 96 is coupled through capacitor 98 to the base of
transistor 94. Operating current is supplied to the oscillator by
lines 50 and 55 and the oscillations thereof are controlled by
capacitor 98. In a particularly preferred application of the
invention, the electrodes of capacitor 98 are secured to the
exterior of an intravenous liquid feeding vessel, the oscillator
circuit elements being selected such that sustained oscillations
accompany the presence of liquid intermediate the capacitor
electrodes. Such sustained oscillations discontinue as the liquid
recedes from such level.
During occurrence of sustained oscillations, transistor 100 of
detector 58 (FIG. 5) conducts periodically, discharging capacitor
102. Upon cessation of oscillations, transistor 100 is rendered
non-conductive and capacitor 102 charges toward line 50 voltage,
i.e., detector output line 64 goes negative.
Voltage-sensitive switch 66a of FIG. 6A includes transistor 104,
the base of which is directly connected to line 64. The collector
of transistor 104 is directly connected to line 68 and the emitter
thereof is connected through resistor 106, switch 108 and resistor
110 to line 70. The transistor is rendered conductive upon the
occurrence of said negative voltage on line 64 and accordingly
applies a negative voltage to the base of transistor 112, in turn
rendering transistor 112 conductive. Line 72 is thereupon set at
approximately the same voltage as line 70, i.e., positive.
Referring again to FIG. 4A, when line 72 is positive as discussed,
a positive signal is thereby applied to the base of transistor 88,
switching transistor 88 into conduction and short-circuiting
resistor 80. This short-circuiting of resistor 80 increases the
current drawn from rectifier 74 and hence from current source 10.
By appropriate selection of component values, the current drawn on
this event is increased far above said nominal amplitude to a level
sufficient for energization of annunciator unit 12a.
In summary of the operation of the first system embodiment, it will
be seen that the occurrence of a liquid level of interest, e.g.,
intravenous feeding liquid decreasing to below a given level, gives
rise to the cessation of sustained oscillations in oscillator 54,
the detection of such cessation by detector 58, the closing of
switch 66 and the further closing of switch 88 of primary
controller 48a. Shunting of resistor 80 may also be accomplished by
the closure of PTC switch 18a of secondary controller 16a, which
provides continuity between lines 44 and 46 through resistor 114.
Resistor 114 may be dispensed with, but when used, is selected to
have a value such that its resistance sufficiently shunts resistor
80 to provide a current flow energizing lamp 20a. Thus, annunciator
unit 12a may be energized either by the primary or the secondary
controller.
In FIG. 6A, switch 108 is illustrated in the position labeled D
(liquid dispensing). Where the collection of liquid to a
preselected level in a vessel is of interest, this switch is placed
on the C (liquid collection) position thereof. In this mode of
operation, the start rather than the cessation of oscillation in
oscillator 54 is detected. Prior to the commencement of
oscillations, i.e., when liquid is not present between the
electrodes of capacitor 98, line 64 of detector 58 is negative,
back-biasing transistor 116 in turn back-biasing transistor 112. As
oscillations commence, line 64 goes positive, switching transistor
116 into conduction. This, in turn, renders transistor 112
conductive, thereby providing a positive signal on line 72 and
energizing annunciator unit 12a.
Where it is desired to provide selective indications at the central
station of both the patient's need for attention and the occurrence
of a liquid level of interest, the optional circuit means shown in
FIG. 7 may be introduced in the above-discussed first embodiment of
the invention. In FIG. 6A, optional dotted lines 118, 120 and 122
are provided for this purpose and interconnect with the circuit
means of FIG. 7 as indicated. The FIG. 7 circuitry comprises a
free-running multivibrator including transistors 124 and 126 and
associated resistors and capacitors connected in known manner to
provide periodic output pulses on line 128. Transistor 130 is
rendered conductive during occurrence of the pulses on line 128 and
line 120 and accordingly is periodically connected to line 122
(positive potential). By use of this optional circuit means, the
base of transistor 112 of voltage-sensitive switch 66a is
periodically connected to a positive potential. When its base is
connected to a positive potential, transistor 112 is rendered
non-conductive, irrespective of the occurrence or non-occurrence of
a liquid level of interest. Assuming, by way of example, that line
64 indicates the occurrence of a liquid level of interest,
rendering transistor 104 conductive, transistor 112 will be
rendered alternately conductive and non-conductive during the
occurrence of such liquid level of interest as determined by
control of line 120 by the FIG. 7 circuit. Line 72 accordingly
provides a periodic positive signal to transistor 88 of primary
controller 48a with the result that transistor 88 is periodically
switched into conduction and lamp 20a flashes at this frequency.
Assuming further that patient switch 18a is continually closed
during the occurrence of a liquid level of interest, resistor 80 of
the primary controller will be effectively short-circuited
periodically by transistor 88 during conduction thereof and will be
continually shunted by resistor 114. Evidently, the current
conducted through annunciator unit 12a will be at least at a first
level determined by the shunting effect of resistor 114, sufficient
to provide dull illumination of lamp 20a and, during periods of
conduction of transistor 88, will be at a higher level, providing
increased visible output in lamp 20a. A pulsating light output of
lamp 20a overriding the constant glow will result, providing
concurrent distinct indications of both the occurrence of the
liquid level of interest and of the patient's need for
attention.
In a second embodiment of the invention, annunciator unit 12b is
employed in conjunction with primary controller 48b (FIG. 4B),
secondary controller 16b (optional) and voltage-sensitive switch
66b (FIG. 6B). Lines 44 and 46 are either connected together or to
secondary controller 16b. In this system embodiment, a current of
predetermined magnitude sufficient to energize coil 30 and maintain
contact arm 28 in engagement with contact 32 is required at all
times other than upon the occurrence of either or both of a
patient's demand for attention and a liquid level of interest.
Where the current through annunciator unit 12b decreases below such
predetermined magnitude, coil 30 is deenergized and contact arm 28
is spring-biased into engagement with contact 26 thereby energizing
lamp 20b. The manner in which current flow through unit 12b is
controlled will be evident from a consideration of the detailed
circuitry of primary controller 48b and switch 66b.
Referring to FIG. 4B, controller 48b has the same lines for
interconnection with remaining elements of the system as in the
case of controller 48a and incorporates various like elements
including rectifier 74, resistor 80, zener diode 82, transistor 88
and biasing resistors 84 and 86. A remote station indicator 132 may
be included where desired. Transistor 88 is again connected such
that it effectively shunts resistor 80 when rendered conductive. On
the other hand, lines 44 and 46, extending from the secondary
controller, do not shunt resistor 80 but are connected respectively
to line 72 and resistor 86. Switch 66b (FIG. 6B) incorporates the
same circuit elements as in the case of switch 66a with the
exception that switch 108 is oppositely poled, providing
communication between transistors 104 and 112 in the liquid
collection mode and providing communication between transistors 112
and 116 in the dispensing mode.
For purposes of explanation, let it be assumed that patient switch
16b is in the position shown in FIG. 3b (unoperated) and that
liquid being collected has not reached a level of interest. Under
these conditions, oscillator 54 is non-oscillating and detector 58
provides a negative potential on line 64 to which switch 66b
responds with conduction occurring in both transistors 104 and 112.
line 72 is accordingly positive and a positive potential is applied
to the base of transistor 88 rendering this transistor conductive
and shunting resistor 80. Current flow through annunciator unit 12b
is accordingly of sufficient magnitude to maintain coil 30
energized and lamp 20b is unenergized. As oscillations commence
upon the occurrence of the liquid level of interest, detector
output line 64 goes positive whereupon transistors 104 and 112 are
rendered non-conductive. Line 72 recedes from its positive level
and transistor 88 is rendered non-conductive and the current
therethrough is greatly reduced, thereby decreasing the loading of
current source 10 such that current flow through annunciator unit
12b decreases to a level insufficient for maintaining coil 30
energized with resulting energization of lamp 20b. Evidently, where
switch 18b of secondary controller 16b is operated by the patient,
continuity between lines 44 and 46 is interrupted and, whatever the
state of line 72, transistor 88 is rendered non-conductive, thereby
inserting resistor 80 in the loading circuit of rectifier 44 and
causing current flow through annunciator unit 12b to decrease below
the level required for continued energization of coil 30.
In the liquid dispensing mode of operation of the second system
embodiment, transistor 112 is rendered conductive during
oscillations and non-conductive upon occurrence of the liquid level
of interest.
FIG. 8 illustrates a physical embodiment of capacitor 98 of
oscillator 54 which is suitable for detection of liquid levels of
solutions. The salinity of these solutions for hospital usage is
frequently of appreciable magnitude, thereby providing a relatively
conductive liquid. Accordingly, the liquid in conjunction with
conductive strip electrodes 134 and 136 and the dielectric wall of
the vessel, e.g., a glass or plastic container, provides a
resistive-capacitive feedback path between oscillator lines 138 and
140. As the liquid level drops below the strip electrodes,
conduction in the feedback path is substantially reduced, giving
rise to the cessation of oscillations. Electrode strips 134 and 136
may be comprised of metallic strip material secured in opposing
relation to the outer wall of the liquid containing vessel.
Where the salinity of the monitored liquid is appreciable, it is
preferable to introduce a further electrode strip 142, secured to
the vessel outer wall adjacent one of electrode strips 134 and 136.
Electrode strip 142, when used, is connected by line 144 to
oscillator 54 and, as indicated in FIG. 5, is connected in turn by
line 55 to rectifier line 78. In operation of the system
incorporating electrode strips 134, 136 and 152, three capacitances
are involved. First and second capacitances are defined as between
the liquid and electrode strips 134 and 136 and a third capacitance
exists as between electrode strip 142 and the liquid. The first and
second capacitances are series connected by the liquid and the
third capacitance is effectively a shunt capacitance connected
intermediate the first and second capacitance to line 78. As liquid
level drops below electrode strips 134 and 136, the third
capacitance acts as a shunt and oscillations cease more rapidly.
This arrangement is particularly effective where some adherence of
the liquid to the interior walls of the vessel occurs for an
interval following the receding of the liquid level below
electrodes 134 and 136. In this event, in the absence of electrode
strip 142, a high resistance-low capacitance path may persist
between lines 138 and 140. Absent the third shunt capacitance, this
path may cause oscillation to persist for a slight time longer
after the receding of the liquid to the level of interest.
In a practical usage of the systems of the invention, the patient
call plug is removed from the remote station receptacle of a
pre-existing annunciator system and the connector-adapter of the
invention is simply installed in the receptacle. All operating
current for the controller and detector apparatus is provided
through the connector-adapter and no ancillary connections are
required, e.g., power cords at the patient's bedside are not
needed. If desired, the patient call plug may be inserted in the
receptacle section of the connector-adapter and used by the patient
while the detector apparatus is operative.
While the invention has been described in connection with the
foregoing hospital related application and more particularly in
connection with liquid level detection, the invention is clearly
applicable to both expanding the capabilities of other pre-existing
annunciator systems and to detection of conditions other than
liquid level change. Moreover, the particularly disclosed
embodiments of the system may be evidently modified by those
skilled in the art without departing from the spirit of the
invention and accordingly, the illustrated embodiments are intended
in a descriptive and not in a limiting sense. The true scope of the
invention is defined in the following claims.
* * * * *