U.S. patent number RE28,656 [Application Number 05/483,213] was granted by the patent office on 1975-12-16 for thermostatless blanket control circuit.
This patent grant is currently assigned to Northern Electric Company. Invention is credited to Gordon S. Carlson, George C. Crowley.
United States Patent |
RE28,656 |
Crowley , et al. |
December 16, 1975 |
Thermostatless blanket control circuit
Abstract
An overload protection circuit for an electric heating blanket
is provided. A sensing element in the blanket is coupled to a
neon-filled diode. When an overload condition is sensed the diode
ceases to emit light and a bimetallic element in series with a
light-responsive resistor causes a pair of contacts in series with
the heating element to open.
Inventors: |
Crowley; George C. (Winnetka,
IL), Carlson; Gordon S. (Northbrook, IL) |
Assignee: |
Northern Electric Company
(Chicago, IL)
|
Family
ID: |
26887810 |
Appl.
No.: |
05/483,213 |
Filed: |
June 26, 1974 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
192181 |
Oct 26, 1971 |
03673381 |
Jun 27, 1972 |
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Current U.S.
Class: |
219/212; 219/494;
361/106; 361/165; 361/173 |
Current CPC
Class: |
G05D
23/1909 (20130101); H05B 3/342 (20130101); G05D
23/24 (20130101); H02H 5/043 (20130101); H05B
2203/014 (20130101) |
Current International
Class: |
G05D
23/20 (20060101); H02H 5/00 (20060101); H05B
3/34 (20060101); G05D 23/24 (20060101); H02H
5/04 (20060101); H01H 037/00 () |
Field of
Search: |
;317/132,4R,41,124
;307/117 ;219/212,494 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trammell; James D.
Attorney, Agent or Firm: Clark; George R. Rose; Neil M.
Pacocha; John S.
Claims
What is claimed as new and desired to be secured by Letters Patent
of the United States is:
1. An overload protection circuit for an electric blanket having a
heating means and a sensing means .Iadd.and a heat sensitive
material .Iaddend.which has a resistance that decreases with
increasing temperature, the sensing means being located in
proximity in said blanket to said heating means and electrically
coupled .[.in parallel with.]. .Iadd.to .Iaddend.said heating means
.Iadd.by said heat sensitive material .Iaddend.comprising a diode
filled with an ionizable gas which emits radiation when said gas is
ionized; said diode being .[.coupled in series with.].
.Iadd.connected between .Iaddend.said sensing means .Iadd.and said
heating means in parallel with said heat sensitive material,
.Iaddend.control means having a pair of overload contacts which are
coupled in series with said heating means and radiation responsive
means coupled to said control means and positioned to receive said
radiation from said diode; said control means being constructed to
control the opening and closing of said overload contacts in
accordance with the condition of said radiation responsive means
wherein said condition changes in accordance with the radiation
received by said radiation responsive means from said diode.
2. An overload protection circuit as set forth in claim 1 wherein
said radiation responsive means is a resistor which has a
resistance that varies as a function of the radiation said resistor
receives from said diode.
3. An overload protection circuit as set forth in claim 2 further
comprising a blanket energizing switch means which has contacts
that momentarily place line voltage across said resistor when said
switch is being changed from its off and its on position.
4. An overload protection circuit as set forth in claim 1 wherein
said control means is a bimetallic control element that is coupled
in series with said radiation responsive means across said series
combination of said diode and said sensing means.
5. An overload protection circuit as set forth in claim 4 wherein
said radiation responsive means is a resistor which has a
resistance that varies as a function of the radiation said resistor
receives from said diode.
6. An overload protection circuit as set forth in claim 5 further
comprising a blanket energizing switch means which has contacts
that momentarily place line voltage across said resistor when said
switch is being changed from its off to its on position.
Description
BACKGROUND OF THE INVENTION
Electric heating blankets are commonly constructed with a
heat-sensitive sensing wire or element and a heating wire or
element. One frequently encountered electric heating blanket
construction consists of a flexible insulating core around which
the heating wire and sensing wire are wound. The heating and
sensing wire are separated by a layer of heat sensitive material.
The resistance of the heat-sensitive material varies inversly with
the temperature of the heating wire and this variation is sensed by
the sensing wire to provide for overload protection. An insulating
covering is preferably supplied over the sensing wire.
Control for a blanket of the type described is conventionally
achieved by a means of a thermally sensitive switch which has a
pair of contacts coupled in series with the heating wire. The
sensing wire may be coupled to the control circuit of a second
thermally sensitive switch which has pair of overload contacts in
series with the heating wire. The second thermal switch provides
overload protection for the blanket. The bimetallic thermal control
switches which are commonly used to control the operation of the
overload contacts are expensive and are capable of handling only a
very small amount of power. Moreover, these switches tend to be
overly sensitive and are difficult to manufacture.
It is therefore an object of the present invention to provide a
relatively inexpensive and uncomplicated thermal overload
circuit.
It is another object of the present invention to provide an
overload protection circuit for an electric blanket wherein a light
source is activated by a sensing wire and a light-responsive switch
means is activated by the light source to open the heating wire
circuit of the blanket wire.
It is a further object of the present invention to provide an
electric blanket control in which a neon-filled diode is coupled in
series with a sensing wire .Iadd.and is connected between the
sensing wire and the heater in parallel with a heat sensitive
material .Iaddend.so that the neon gas in the diode is de-ionized
when an overload condition exists, and in which a light-responsive
means reacts to the absence of light from the ionized neon by
opening the heating wire circuit.
DESCRIPTION OF THE DRAWING
The FIGURE is a schematic diagram of an embodiment of the present
invention .
TECHNICAL DESCRIPTION OF THE INVENTION
In order for an electric blanket to be suitable for personal use
the blanket must be safe and it must be easy to operate. An
electric heating blanket may become overheated during use thereby
creating a dangerous risk to the user of the blanket. Therefore,
virtually all commercially available blankets provide for some form
of overload protection. The various control circuits that are
conventionally employed, however, are relatively expensive to
manufacture and are relatively difficult to manufacture. A reliable
and inexpensive overload control circuit is provided by the present
invention.
An electric blanket which incorporates the present invention is
indicated by the reference number 10 of the FIGURE. The electric
blanket 10 is constructed in a somewhat conventional manner in that
it has a heating wire 12 and a sensing wire 14 incorporated
therein. The length of the sensing wire is approximately equal to
one-half the length of the heating wire 12, which is shown
schematically in the FIGURE by the two half length sections 12a and
12b. The sensing wire 14 is wound through only one half of the
electric blanket 10, but unlike most sensing wires the sensing wire
14 is able to carry enough electrical current to function as a
heating wire also. The sensing wire 14 may by physically located in
a portion of the heating blanket with either of the half-length
segments of the heating wire in proximity to it. The resistance of
the heating section which is in proximity to the sensing wire 14
will be however slightly different from the resistance of the other
section of heating wire in order to provide for temperature
equalization across the entire heating blanket 10.
The heating wire 12 is connected in series with the thermal control
element 16 of the thermal switch across the input voltage line. The
element 16 is a conventional bimetal thermal control element that
is responsive to the current that flows through the heating wire 12
and is adjustable by the user by means of a conventional adjustment
screw 18c. The switch 18 causes the connection between the points
18a and 18b to be repeatedly made and broken in a cyclic manner.
The length of time that the connection is made during a given time
period is determined by the setting of the adjustment screw.
In addition to the control switch 18 an overload switch 20 must be
provided to insure that an overload condition does not damage the
blanket and possibly result in a dangerous condition for the user
of the blanket. When the blanket 10 is energized the overload
switch 20 closes the heating wire circuit through the points 20a
and 20b since the On-Off switch 28 is in its On position and
electrical connection is also made between the points 28a and 28b.
The bimetallic thermal control element 22 that controls the making
and breaking of the switch 20 is coupled to the neon-filled diode
24. The diode 24 is coupled to the sensing wire 14 which in turn is
coupled to the current limiting resistor 30. The diode 24 is
normally energized so that the neon gas in the diode 24 is ionized
and the diode 24 is consequently emitting light. .Iadd.A heat
sensitive material located between the .Iaddend..[.The.]. sensing
wire 14 .Iadd.and the heating wire 12 .Iaddend.is made of a
material which has a decreased resistance when its temperature
increases. When an overload condition occurs the .[.sensing wire
14.]. .Iadd.heat sensitive material .Iaddend.heats up and the
resistance of the .[.sensing wire.]. .Iadd.material .Iaddend.then
reduces sufficiently to cause the ionized gas in the diode 24 to be
extinguished. When this occurs light will no longer be emitted by
the diode 24. The light emission state of the diode 24 is used in
the manner described below to control a light-responsive switch
which opens and closes the heating wire circuit and it also may be
used to give the user a visual indication of the overload condition
if desired.
The current through bimetallic control element 22 controls contacts
of the switch 20 which makes and breaks the electrical connection
between the points 20a and 20b. When the neon gas in the diode 24
is ionized, light from the diode 24 is received by the
light-responsive resistor 26, which may be a cadmium sulphide cell
or other suitable element. The resistance of the light responsive
resistor 26 is such that the current through the bimetallic element
22 causes sufficient heating of the element 22 so that it deflects
enough to keep the switch 20 closed thereby completing the circuit
between the points 20a and 20b when the neon gas in the diode 24 is
ionized. If overload occurs, however, the absence of emitted light
from the diode 24 causes the resistance of the light-responsive
resistor 26 to increase sufficiently so that the current through
the bimetallic element 22 decreases to the point where the element
22 cools off and deflects in a direction that causes the switch 20
to open the electrical connection between the points 20a and 20b of
the heating wire circuit.
Since the operation of the light-responsive resistor 26 is critical
it is desirable to be able to make the overload circuit fail-safe
in the event that the resistance of the resistor 26 decreases
materially or shorts out. For this purpose the On-Off switch 28 has
a contact 28c which momentarily contacts the moving contact of the
switch 28 when the switch is being turned on. This momentarily
places the full line voltage across the resistor 26, and if the
resistance of the resistor 26 is below a predetermined minimum
value, it will be burned out causing an open circuit thereby making
the overload circuit inoperative to close switch 20. This
arrangement thus prevents energization of the heating elements 12
in the event that the overload circuit is not in condition to
operate.
While a particular embodiment of the present invention has been
described it is not intended that the invention be limited thereto
since many modifications may be made and it is intended to cover
any such modification that falls within the true scope and spirit
of the appended claims.
* * * * *