U.S. patent number 3,903,883 [Application Number 05/461,753] was granted by the patent office on 1975-09-09 for variable aerosol heater with automatic temperature control.
This patent grant is currently assigned to Respiratory Care, Inc.. Invention is credited to Robert J. Froehlich, Richard W. Pecina.
United States Patent |
3,903,883 |
Pecina , et al. |
September 9, 1975 |
Variable aerosol heater with automatic temperature control
Abstract
An inhalation therapy device of the type in which a column of
water is heated, atomized, and combined with a flow of oxygen to
form a stream of humidified oxygen which is administered to a
patient. An adaptor located at the patient site is connected to the
hose carrying the stream. The adaptor includes a thermistor which
senses the temperature of the stream immediately prior to the
administration to the patient. The thermistor output signal is fed
back to a heater control system which controls the amount of heat
applied to the column of water in a manner which maintains the
temperature constant. The particular temperature being maintained
is manually selectable.
Inventors: |
Pecina; Richard W. (Waukegan,
IL), Froehlich; Robert J. (Rosemont, IL) |
Assignee: |
Respiratory Care, Inc.
(Arlington Heights, IL)
|
Family
ID: |
23833804 |
Appl.
No.: |
05/461,753 |
Filed: |
April 17, 1974 |
Current U.S.
Class: |
128/200.21;
219/497; 261/130; 128/203.27; 219/502; 261/142; 392/396 |
Current CPC
Class: |
A61M
16/1075 (20130101); A61M 16/109 (20140204); A61M
16/16 (20130101) |
Current International
Class: |
A61M
16/10 (20060101); A61M 16/16 (20060101); A61M
015/00 () |
Field of
Search: |
;128/193,194,192,212,1B
;219/497,502 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Gaudet; Richard A.
Assistant Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Schellin; Eric P.
Claims
What is claimed is:
1. In combination with an inhalation therapy device of the type
wherein a column of water is drawn from a receptacle through an
electric heating unit, whereby the water is heated, and into an
atomizing device, whereby the heated water is atomized, and wherein
the heated water is combined with a flow of oxygen to provide a
stream of humidified oxygen and wherein said stream of humidified
oxygen is delivered through an extended hose to the site of a
patient, and wherein the stream of humidified oxygen is thereat
administered to said patient, the improvement which comprises:
means for sensing the temperature of the stream of humidified
oxygen at the said patient site immediately prior to its
administration to the said patient and for generating an electrical
signal representative of said temperature; and,
control means responsive to said signal for controlling the amount
of heat generated by said electric heating unit to maintain the
stream at a preselected temperature;
wherein said control means comprises:
gate controlled bilateral switch means for controlling the flow of
electric current through said electric heating unit;
means for amplifying said electrical signal; and,
means connected to the gate electrode of said bilateral switch
means for controlling the conductive state of said swtich means in
response to said amplified electrical signal;
means for sensing the temperature of said electric heating unit and
generating an output signal indicative thereof; and,
means for overriding said amplified electrical signal and causing
said bilateral switch means to be in its non-conductive state when
said output signal indicates a preselected maximum temperature.
2. In combination with an inhalation therapy device of the type
wherein a column of water is drawn from a receptacle through an
electric heating unit, whereby the water is heated, and into an
atomizing device, whereby the heated water is atomized, and wherein
the heated atomized water is combined with a flow of oxygen to
provide a stream of humidified oxygen which is administered to a
patient, the improvement which comprises:
means for sensing the temperature of the stream of humidified
oxygen immediately prior to its administration to the patient and
for generating an electrical signal representative of said
temperature; and,
control means responsive to said signal for controlling the amount
of heat generated by said electric heating unit to maintain the
stream at a preselected temperature, said control means
comprising:
gate controlled bilateral switch means for controlling the flow of
electric current through said electric heating unit;
means for amplifying said electrical signal;
means connected to the gate electrode of said bilateral switch
means for controlling the conductive state of said swtich means in
response to said amplified electrical signal;
means for sensing the temperature of said electric heating unit and
generating an output signal indicative thereof;
means for overriding said amplified electrical signal and causing
said bilateral switch means to be in its non-conductive state when
said output signal indicates a preselected maximum temperature;
and,
circuit means for temporarily modifying the operation of said
overriding means such that the bilateral switch means is not caused
to become non-conductive until said output signal indicates another
preselected maximum temperature which is higher than said
first-mentioned preselected maximum temperature.
3. The combination of claim 2, wherein said control means includes
means for visually indicating if the device is properly
grounded.
4. The combination of claim 3, wherein said ground indicating means
includes:
an indicator lamp;
an amplifier in series with said lamp;
circuit means for biasing said amplifier into conduction when the
device is connected to ground;
a photo-tranistor connected to said amplifier so as to cause said
amplifier to become non-conductive when said photo-transistor is
conductive;
a light emitting diode optically coupled to said photo-transistor;
and,
switch means responsive to the activation of said circuit operation
modifying means for energizing said light emitting diode only when
said circuit operation modifying means is energized.
5. In combination with an inhalation therapy device of the type
wherein a column of water is drawn from a receptacle through an
electric heating unit, whereby the water is heated, and into an
atomizing device, whereby the heated water is atomized, and wherein
the heated atomized water is combined with a flow of oxygen to
provide a stream of humidified oxygen which is administered to a
patient, the improvement which comprises:
means for sensing the temperature of the stream of humidified
oxygen immediately prior to its administration to the patient and
for generating an electrical signal representative of said
temperature; and,
control means responsive to said signal for controlling the amount
of heat generated by said electrical heating unit to maintain the
stream at a preselected temperature, said control means
comprising:
gate controlled bilateral switch means for controlling the flow of
electric current thorugh said electric heating unit;
means for amplifying said electrical signal; and,
means connected to the gate electrode of said bilateral switch
means for controlling the conductive state of said switch means in
response to said amplified electrical signal, said means for
controlling the conductive state of said gate controlled bilateral
switch means comprising:
capacitor means for providing triggering current to the gate
electrode of said bilateral switch means;
a diode bridge rectifier circuit having one input lead connected to
said capacitor means so that said capacitor means is charged by the
rectifier current;
a photo-transistor connected in series with said bridge rectifier
output; and
a light emitting diode optically coupled to said photo-transistor
for controlling the conductive state of said photo-tranistor in
response to said amplified electrical signal.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of inhalation
therapy and more particularly to apparatus which humidifies oxygen
before it is adminsistered to a patient.
Inhalation therapy is the medical art of treating a patient with
oxygen, or a mixture of air and oxygen, having a high moisture
content. This is generally accomplished by atomizing or nebulizing
pure water and causing the oxygen to come into contact with it,
whereby the oxygen is humidified. A particular system for
accomplishing this is disclosed in application Ser. No. 286,692
filed Sept. 6, 1972 by Edward van Amerongen, for "Nebulizer",
assigned to the assignee of the present application, now U.S. Pat.
3,771,721, issued on Nov. 13, 1973. Briefly, the aforementioned
application shows a system in which a receptacle containing water
is adapted as a source of atomized liquid through the agency of a
nebulizer which couples oxygen pressure to the receptacle. A
venturi within the nebulizer draws water from the receptacle and
directs atomized water and oxygen toward an outlet from which the
humidified oxygen flows.
It has been found that the results of the inhalation therapy are
improved if the humidified oxygen is warmed before it is
administered to the patient. This has generally been accomplished
by heating the water in the receptacle before it is atomized. The
receptacle is placed in a heater which heats the water by heating
the walls of the receptacle. This approach has many disadvantages.
For one, it is very inefficient since the useful heat must flow
through the walls of the receptacle before reaching the water. This
results in bulky equipment and heavy power requirements. A more
serious disadvantage is that it is difficult to maintain a desired
temperature for the humidified oxygen stream by the method because
the heated water flows a relatively long distance, during which its
temperature can be affected by the environment, before coming into
contact with the oxygen.
Many of the problems of the prior art, including those noted above,
were solved by an invention disclosed in application Ser. No.
396,782, now U.S. Pat. No. 3,864,544, for "Electric Heating Unit
for Liquid", filed Sept. 13, 1973 by Edward van Amerongen, and
assigned to the assignee of the present application. Briefly,
application Ser. No. 396,782, now U.S. Pat. No. 3,864,544, shows an
electric heating unit adapted to be placed between the water
receptacle and the nebulizer. The unit includes an electric heating
element which heats a tubular member which conduits a rising column
of water from the receptacle to the nebulizer. The heating element
is disposed in a bore in a metal block. The block has another bore
in which a section of the tubular member is disposed. The heating
element heats the block which, in turn, heats the tubular member. A
thermostat is placed close to the block and controls the
temperature of the rising column of water by controlling the flow
of the electric current to the heating element.
While the electric heating unit of van Amerongen has proven to be a
large advance in the art of inhalation therapy, there are many
problems remaining. It has been found by medical practitioners that
it is desirable, in terms of achieving the most effective therapy,
to have a particular temperature for the humidified oxygen stream
when it is administered to the patient. In most cases, the
temperature of the humidified oxygen stream should be the same as
the physiological temperature of the patient, generally
98.6.degree.. In a few instances, such as in pediatrics, the
temperature of the stream should be lower, such as 92.degree.. Due
to the lack of accuracy of prior art devices and the many variables
involved in the inhalation therapy environment, no prior art device
has proven capable of providing a stream of humidified oxygen which
has a constant and controllable temperature when being administered
to the patient. Since the stream is heated by heating the water
before it is nebulized and combined with oxygen, such variables as
the length of the hose connecting the nebulizer to the patient, the
room temperature, the presence or absence of, and degree of, air
movement over the hose, variable pressure of the oxygen supply, and
the variability of the heater itself, all influence the temperature
of the stream at the patient site.
SUMMARY OF THE INVENTION
It is the general purpose of the present invention to provide a
device for inhalation therapy which permits the temperature of the
humidified oxygen stream at the patient site to be accurately and
automatically controlled. To attain this, the invention provides a
unique heater control circuit which controls the heating of the
water in accordance with the temperature of the humidified oxygen
stream at the patient site. A temperature sensing adaptor is
connected between the hose carrying the stream of humidified oxygen
and the device used to administer the humidified oxygen to the
patient. An electrical signal representative of the sensed
temperature is fed back from the adaptor to the heater control
circuit and used to automatically maintain the temperature
constant. The particular temperature being maintained is variable
and can be selected at the will of the operator. Another
temperature sensor senses the temperature of the heating element
and will override the stream temperature sensor if the heating
element becomes hot enough to cause vapor lock or otherwise
overheats.
Therefore, it is an object of the present invention to provide an
inhalation therapy device which maintains the temperature of the
humidified oxygen stream at the patient site constant.
It is another object of the present invention to provide an
inhalation therapy device which delivers a stream of humidified
oxygen to the patient site at a controllably variable
temperature.
It is a further object of the present invention to provide an
inhalation therapy device which automatically compensates for
environmental variables to deliver a stream of humidified oxygen to
the patient site at a constant temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings, in which like reference numerals
designate like parts throughout the figures thereof, and
wherein:
FIG. 1 shows an overall view of a preferred embodiment of the
invention;
FIG. 2 shows the preferred embodiment cut away along line 2--2 of
FIG. 1;
FIG. 3 is a schematic diagram of the sensor and control circuitry
of the invention;
FIG. 4 is a schematic diagram of the power supply circitry of the
invention;
FIG. 5 is a schematic diagram of the heater power circuitry of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIGS. 1 and 2, the heating and control unit is
designated by the numeral 10. The heating portion 12 of the unit 10
is connected between nebulizer 16 and water receptacle 18. As is
more fully disclosed in the aforementioned van Amerongen
application, a source of oxygen under pressure is connected to the
nebulizer 16 and flows through it into hose 20. The oxygen flow
creates a pressure drop in the nebulizer which causes a column of
water to be drawn from receptacle 18 through tubular member 38. An
electric heating element 42 is located in a horizontal bore in
metal block 40. A portion of tubular member 38 is disposed in a
vertical bore in block 40. As the rising column of water passes
through tubular member 38, it is heated by heat passing from heater
element 42 through block 40 to tubular member 38. A power cord 34
having a ground prong 33 is provided to couple electric power from
a conventional source of electrical energy.
The control portion of unit 10 is generally designated by numeral
14, and includes a printed circuit board 48 upon which electrical
circuit elements are mounted in the conventional manner. Also
mounted on the board 48 are three neon tubes 50, 52 and 54. When in
a completely assembled condition, these tubes are disposed behind
semi-transparent areas 56, 58 and 60, respectively, on the face of
the unit, these areas having indicia thereon to indicate circuit
conditions. The particular function of these tubes, as well as the
circuit components, will be fully described below. Projecting from
the face of the unit is temperature control knob 32. Disposed in
heating block 40 is a temperature sensing device 44, such as a
thermistor. The device 44 provides an electrical output signal on
wire 45 which is indicative of the temperature of the block 40.
Also disposed in heat conducting relationship with block 40 is
thermal fuse 46. Fuse 46 is connected in series with heater element
42 to disconnect current from the heater element in case of
overheating. The fuse also protects the unit in case of a circuit
malfunction, since the fuse operates directly from sensed heat and
does not rely on control circuit operation.
An adaptor 22 having a temperature sensing device 26 is connected
at the patient site between the end of hose 20 and the coupler,
hoses, etc., 24 of the device which administers the humidified
stream of oxygen to the patient. The temperature sensing device 26
is of the type, such as a thermistor, which provides an electrical
signal indicative of the temperature being sensed. The exact
structure of the adaptor 22 is not critical, being primarily a
matter of design based on such factors as the relative sizes and
shapes of the hoses and connectors. The important considerations
are that the adaptor be located at the patient site and that the
temperature sensing device 26 be disposed so as to sense the
temperature of the stream of humidified oxygen. In this fashion, an
electrical signal representing the temperature of the stream of
humidified oxygen at the patient site is transmitted via conductor
28, plug 30 and socket 36, to the control circuitry in portion 14
of unit 10.
The electrical circuitry aspect of the invention will now be
described. Referring to FIG. 4, the power supply circuit receives
A.C. power line input on terminals H and N. The A.C. power is
applied across the primary windings of transformer 402 and across
neon indicator tube 50. To permit the unit to be used with either
115 VAC or 220 VAC power, the primary windings can be
interconnected in two ways. If 115 VAC is applied, terminal A is
connected to terminal C and terminal B is connected to terminal D.
Connected in this manner, winding A-B is in parallel with winding
C-D. If 220 VAC is applied, terminal B is connected to terminal C.
Connected in this manner, winding A-B is in series with winding
C-D. In either mode of operation, the proper secondary voltage
results and is applied to bridge rectifier circuit 404. The bridge
rectifier output is filtered by filter capacitor 406 to provide
operating voltage Vcc. A regulating circuit comprised of the
parallel combination of Zener diode 410 and capacitor 412 in series
with resistor 408 provides regulated voltage Vreg of an amplitude
less than that of Vcc.
Referring now to the sensor and control circuitry of FIG. 3, the
previously mentioned hose thermistor 26, located at the patient
site, is connected to the control circuitry by plug 30 and socket
36. The socket 36 has contacts 35 and 37 which contact the signal
carrying conductor of plug 30. The ground conductor of plug 30
contacts the ground conductor of socket 36. As an examination of
the diagram will show, when plug 30 is inserted into socket 36,
thermistor 26 is connected to socket 36, terminal 35 and resistor
76 is disconnected from terminal 35. The function of resistor 76 is
to provide a low resistance to control circuitry 14 which will
cause a shut-down of the heater power if plug 30 is removed from
control unit 10. Socket terminal 35 is connected in series with
trim resistor 72, resistor 74, and temperature control variable
resistor 31 across Vreg. The setting of variable resistor 31 is
varied by previously mentioned knob 32. The junction of a resistor
31 and thermistor 26 is connected to input terminal 70 of
differential amplifier 66. Resistors 62 and 64 provide a voltage
divider across Vreg, the junction of resistors 62 and 64 being
connected to terminal 68 of amplifier 66. A feedback path from the
output of amplifier 66 to input terminal 68 is provided by resistor
78 and capacitor 80. The output of amplifier 66 is coupled by
resistor 82 to terminal 84 of differential amplifier 86. The other
input terminal 88 receives a ramp voltage from a ramp generator
circuit designated generally by the numeral 91. The ramp generator
includes a programmable UJT 94 with its gate electrode connected to
the junction of programming resistors 90 and 92. The cathode of 94
is connected to ground through series diodes 102 and 104. The anode
of 94 is connected to terminal 88 of amplifier 86 and coupled to
Vreg through resistor 98. A capacitor 96 is connected across the
anode-cathode circuit of 94. A resistor 100 connects the anode of
diode 102 to Vreg. The output of differential amplifier 86 drives
light emitting diode 108, which is connected to Vcc through
resistor 106.
Vreg is also applied to a series combination of resistor 110 and
capacitor 112. For reasons to be discussed later, resistor 110 has
a very high value of resistance and capacitor 112 has a high value
of capacitance. The junction of resistor 110 and capacitor 112 is
connected via resistor 114 to input terminal 116 of differential
amplifier 118. The other input terminal 124 is connected to the
junction of voltage dividing resistors 120 and 122. Resistor 126
provides a feedback path from the output terminal of amplifier 118
and input terminal 116. The output of amplifier 118 is coupled by
resistor 128 to the base of transistor 130. A light emitting diode
132 is connected in parallel with transistor 130 and in series with
resistor X. The series parallel combination resistor X, transistor
130 and light emitting diode 132 is connected across Vcc.
The output of amplifier 118 is also coupled by resistor 134 to the
base of transistor 136, the collector of which is coupled by
resistor 138 to input terminal 140 of differential amplifier 142.
Resistors 144 and 146 form a voltage divider across Vreg, and their
junction is also connected to terminal 140. Also connected in
series across Vreg are trim resistor 150, resistor Y and previously
mentioned block thermistor 44. The junction of resistor Y and block
thermistor 44 is connected to input terminal 148. The output of
amplifier 142 is coupled by resistor 152 to the base of transistor
154, the collector of which is connected to previously mentioned
terminal 84 of amplifier 86.
FIG. 5 shows the heater power and ground detector circuitry. In the
ground detector circuit, the grounding prong 33 of the power line
plug is coupled to the collector of photo-transistor 133 by
resistor 158 and diode 156. The emitter of photo-transistor 133 is
connected to power conductor H. The collector of photo-transistor
133 is connected to the input of Darlington amplifier 160. Resistor
159 shunts the photo-transistor. Ground indicator neon tube 54 is
connected in series with the Darlington amplifier. Diode 162
couples the neon tube 54 and amplifier 160 to power line conductor
N. A resistor 164 couples the cathode of diode 162 to power-line
conductor H.
In the heater power circuit, heater element 42 and thermal fuse 46
are connected in series with a bidirectional gate-controlled
semiconductor device 166 across the power line conductors. A triac
is the preferred device. The gate electrode of triac 166 is coupled
by a silicon bilateral switch 168 to one plate of capacitor 170.
One input to full wave bridge rectifier 172 is connected to the
junction of 168 and 170. A photo-transistor 109, shunted by
resistor 171, is connected in series with the rectifier output.
Capacitors 174 and 180, and resistors 176 and 178, provide
filtering. Neon tube 52 is connected in parallel with heater
element 42.
The heater power circuit operation will now be described. The
current through heater element 42 is controlled by conductive state
of triac 166. Triac 166 is controlled by bridge rectifier 172 in
the following manner. The triac fires when the charge on capacitor
170 builds up sufficiently to break down semiconductor switch 168
and supply gate current to the triac. Capacitor 170 is charged by
the current drawn by rectifier circuit 172. The rectifier current
passes through the parallel combination of resistor 171 and
photo-transistor 109. When photo-transistor 109 is nonconductive,
the relatively high resistance value limits the current drawn by
the rectifier circuit to a value insufficient to charge capacitor
170 to the bilateral switch breakdown voltage during a half cycle
of the power line voltage. The presence of resistor 171 tends to
limit voltage excursions across the photo-transistor. The bridge
rectifier connected to the photo-transistor in the manner shown in
the drawing permits a bilateral device (triac 166) to be controlled
during both polarities of the input waveform by a unilateral device
(photo-transistor 109). In order for capacitor 170 to charge
sufficiently to cause breakdown of switch 168 and conduction of
triac 166, the photo-transistor 109 must be in a conductive state
so that the rectifier circuit can draw the necessary current. Thus,
by controlling the conductive state of photo-transistor 109,
control of the triac 166, and hence control of the current through
heater element 42, is achieved. Indicator light 52, being in
parallel with the heater element, lights only when the heater
element is receiving current and generating heat.
The primary purpose of the control and sensor circuitry of FIG. 3
is to control the conductive state of photo-tranistor 109 as a
function of the temperature of the humidified oxygen stream at the
patient site. However, the circuitry of FIG. 3 performs three other
functions as well. These functions are: to sterilize the
water-handling tubular member in the heating unit; to provide,
along with the ground detector circuitry of FIG. 5, a temporary
indication as to whether the unit is properly grounded; and, to
limit the maximum temperature of the heating block. How the circuit
accomplishes these functions is most easily understood by
describing first how the circuit operates to accomplish its primary
purpose, and then how this operation is modified to achieve the
other functions.
Referring now to FIG. 3, the signal from hose thermistor 26,
indicative of the temperature of the humidified oxygen stream at
the patient site, is applied to terminal 70 of differential
amplifier 66. It has been found in practice that the amount of gain
of amplifier 66 is very important for obtaining superior system
operating results and the optimum gain was established by
experimentation. The output of amplifier 66 is applied to terminal
84 of amplifier 86. The other terminal receives a ramp voltage from
ramp generator 91. The ramp voltage rises from approximately 1.8
volts (provided by diodes 102 and 104) to approximately 5.4 volts.
The circuits are so designed that the signal on terminal 84 will be
somewhere within that range so that at some point during the rising
ramp, a zero difference occurs. The location of this point
determines the waveform of the signal on the output terminal of
amplifier 86 which is applied to light emitting diode 108. The
light emitted from diode 108 strikes photo-transistor 109 to
control the current through the heater element as previously
described.
The optical coupling provides electrical isolation between the
control and sensor circuitry and the heater power circuitry. A
commercially available optical coupling device which contains both
the light emitter and photo-transistor within a sealed compartment
is used.
The maximum temperature which the heating block is allowed to reach
is determined by the block termistor circuit. Block thermistor 44
provides a signal representative of block temperature. This signal
is applied to terminal 148 of amplifier 142. The other terminal 140
receives a reference potential from the junction of resistors 144
and 146. Trim resistor 150 is adjusted so that, when the block
temperature is below the prescribed maximum the output signal from
amplifier 142 biases transistor 154 to be nonconductive. When the
block temperature rises to the prescribed maximum, the output
signal from amplifier 142 causes transistor 154 to become
conductive. When conductive, transistor 154 clamps terminals 84 of
amplifier 86 close to ground, the result being that the output of
amplifier 86 approaches Vcc, whereby the voltage across diode 108
is insufficient to cause light emission. Thus, photo-transistor 109
ceases to conduct and current through the heater element is cut
off. When the block temperature lowers, transistor 154 goes out of
conduction and the hose thermistor again controls the current
through the heating element.
It is advantageous to sterilize the tubular member of the heating
unit when the unit is being turned on to begin operation. The
circuit which accomplishes this includes amplifier 118, transistor
136, and associated circuitry. When the unit is connected to the
power source, a large capacitor 112 begins to charge through high
value resistor 110. The junction of resistor 110 and capacitor 112
is coupled to input terminal 116 of differential amplifier 118. The
other input terminal 124 receives a steady reference potential from
the junction of resistors 120 and 122 connected across Vreg.
Amplifier 118 is so biased that, with the initial conditions
described above, its output signal causes transistor 136 to
conduct. The conduction of transistor 136 causes resistor 138 to be
effectively in parallel with resistor 146 since one end of resistor
138 is clamped close to ground through the transistor. This changes
the reference potential on terminal 140 of amplifier 142 so that
the heating block reaches a much higher temperature before the
signal from block thermistor 44 causes the output of amplifier 142
to bring transistor 154 into conduction. When the capacitor 112 has
charged to a preselected voltage, the output signal from amplifier
118 turns transistor 136 off, whereby the reference point connected
to terminal 140 of amplifier 142 changes to a value determined
solely by Vreg, resistor 144 and resistor 146, and the block
thermistor circuit operates as previously described.
It is advantageous for the ground indicator lamp 54 to indicate
proper grounding only for a short period of time after the unit is
connected for operation. Referring to FIG. 5, indicator lamp 54 is
connected in series with a Darlington amplifier 160 between
rectifier 162 and conductor H of the power line. When prong 33 is
connected to earth ground, a small amount of current will flow from
resistor 158 through diode 156 and resistor 159 to conductor H.
This current will cause the Darlington amplifier to conduct thereby
causing neon tube 54 to light. The conduction path is from
conductor N through diode 162. If earth ground is not present at
33, no current will flow and the Darlington amplifier will not
conduct.
The previously described output signal from amplifier 118 is
coupled to the base of transistor 130, causing the transistor to
conduct. Since light emitting diode 132 is shunted by transistor
130, the diode does not emit light when the transistor is
conducting. Light emitting diode 132 is optically coupled to
photo-transistor 133 so that, during the sterilizing period,
photo-transistor 133 receives no light and is, in effect, an open
switch. If prong 33 is grounded at this time, the circuit will
operate as described above and indicator lamp 54 will light. If
prong 33 is not grounded, lamp 54 remains off.
When the sterilizing period is over, the signal from amplifier 118
causes transistor 130 to become nonconductive. The voltage
appearing across diode 132 now causes the diode to emit light. This
light is received by optically coupled photo-transistor 133,
causing it to become conductive. The conductive photo-transistor
shunts resistor 159 and effectively clamps the input terminal of
Darlington amplifier 160 to its emitter terminal 161, whereby the
amplifier becomes non-conductive and indicator lamp 54 becomes
dark. As is evident, the ground detector circuit is used for
indication purposes only and does not modify the operation of the
other circuits in any way.
What has been described is an inhalation therapy unit which
automatically maintains the temperature of the humidified oxygen
stream at the patient site constant. The present invention thus
solves many of the problems previously experienced in this field of
technology. The temperature being maintained is variable to suit
the needs of different patients. Obviously, many modifications and
variations of the present invention are possible in light of the
above technique. It is to be, therefore, understood that, within
the scope of the appended claims, the invention may be practiced
otherwise than as specifically described.
* * * * *