Abstrict
An electric heater assembly which provides an alarm warning when
an abnormal condition occurs and which simultaneously disables the
electrical heating elements is provided. The heater element assembly
includes a heating element, an electrically actuated alarm which
provides an alarm warning when an abnormal condition occurs, and
a tip-over switch which provides a closed circuit when the heater
is in a predetermined level position and which provides an open
circuit when the heater is tilted beyond a selected tilt angle.
The electrical heating element, electrically actuated alarm, and
tip-over switch are electrically connected such that the tip-over
switch disables the heating element and actuates the alarm when
the tip-over switch is in one of the open and closed positions,
and such that the tip-over switch enables the heating element and
disables the alarm when the tip-over switch is in the other of the
open closed positions.
Claims
I claim:
1. An electric heater assembly comprising:
at least one electrical heating element;
an electrically actuated alarm for providing an alarm warning upon
actuation;
a tip-over switch having a closed position in which a short circuit
is provided therethrough when said heater is in a predetermined
level position and having an open position in which an open circuit
is provided therethrough when said heater is tilted beyond predetermined
tilt angle; and
circuit means for electrically connecting said heating element,
said tip-over switch and said alarm such that said tip-over switch
disables said heating element and actuates said alarm when said
tip-over switch is in one of said open and closed positions and
such that said tip-over switch enables said heating element and
disables said alarm when said tip-over switch is in the other of
said open and closed positions.
2. The electric heater assembly of claim 1 wherein said circuit
means electrically connects said heating element, said tip-over
switch and said alarm such that said tip-over switch disables said
heating element and actuates said alarm when said tip-over switch
is in said open position and such that said tip-over switch enables
said heating element and disables said alarm when said tip-over
switch is in said closed position.
3. The electric heater assembly of claim 1 further comprising:
a temperature control switch including a sensing element, said
temperature control switch having a closed position in which a short
circuit is provided therethrough when said sensing element senses
the temperature of said heater to be below a predetermined threshold
value and having an open position in which an open circuit is provided
therethrough when said sensing element senses the temperature of
said heater to exceed said threshold value; and
temperature control circuit means for electrically connecting said
heating element, said temperature control switch and said alarm
such that said temperature control switch disables said heating
element and actuates said alarm when said temperature control switch
is in said open position and such that said temperature control
switch enables said heating element and disables said alarm when
said temperature control switch is in said closed position.
4. The heater assembly of claim 1 wherein said circuit means comprises
a tip-over switch circuit wherein said alarm and said tip-over switch
are electrically connected in parallel and wherein said parallel
combination is connected in series with said heating element.
5. The electric heater assembly of claim 4 wherein said alarm is
of the type which fails in an open circuit condition.
6. The electric heater assembly of claim 4 further comprising a
temperature control switch including a sensing element, said temperature
control switch having a closed position in which a short circuit
is provided therethrough when said sensing element senses the temperature
of said heater to be below a predetermined threshold value and having
an open position in which an open circuit is provided therethrough
when said sensing element senses the temperature of said heater
to exceed said threshold value, wherein said temperature control
switch is connected in series with said tip-over switch and said
series combination of said tip-over switch and said temperature
control switch is connected in parallel with said alarm.
7. The electric heater assembly of claim 4 further comprising a
heater thermostat connected in series with and between said heating
element and said parallel combination of said alarm and said tip-over
switch.
8. The electric heater assembly of claim 7 further comprising a
temperature control switch including a sensing element, said temperature
control switch having a closed position in which a closed circuit
is provided therethrough when said sensing element senses the temperature
of said heater to be below a predetermined threshold value and having
an open position in which an open circuit is provided therethrough
when said sensing element senses the temperature of said heater
to exceed said threshold value, wherein said temperature control
switch is connected in series with said tip switch and said series
combination of said tip switch and said temperature control switch
is connected in parallel with said alarm.
9. The electric heater assembly of claim 1 wherein said alarm comprises
an electrically actuated audible alarm.
10. The electric heater assembly of claim 4 wherein said alarm
comprises an electrically actuated audible alarm.
11. The electric heater assembly of claim 10 wherein said alarm
further comprises a pilot light connected in parallel with said
electrically actuated audible alarm.
12. The electric heater assembly of claim 8 further comprising
an electric fan including an electric fan motor wherein said electric
fan motor is connected in series with and between said electric
heating element and said thermostat.
13. The electric heater assembly of claim 8 including a second
heating element connected in series with said first heating element
and means for selectively short circuiting one of said heating elements.
14. The electric heater assembly of claim 13 further comprising
an electric fan including an electric fan motor, wherein said fan
motor is connected in parallel with said heating elements.
15. An electric heater assembly comprising:
at least one electrical heating element;
an electrically actuated alarm for providing an alarm warning when
said heater is tilted beyond a predetermined position; and
a tip-over switch providing a closed circuit therethrough when
said heater is in a predetermined level position, and providing
an open circuit therethrough when said heater is tilted beyond a
predetermined tilt angle;
wherein said alarm and said tip-over switch are electrically connected
in parallel and wherein said heating element is connected in series
with said parallel combination of said tip-over switch and said
alarm.
16. The electric heater of claim 15 further comprising a heater
thermostat electrically connected in series with and between said
heating element and said parallel combination of said tip-over switch
and said alarm.
17. The electric heater assembly of claim 15 further comprising
a temperature limit control switch including a sensing element,
said temperature control switch having a closed position in which
a short circuit is provided therethrough when said sensing element
senses the temperature of said heater to be below a predetermined
threshold value and having an open position in which an open circuit
is provided therethrough when said sensing element senses the temperature
of said heater to exceed said threshold value, wherein said temperature
control switch is connected in series with said tip-over switch
and said series combination of said tip-over switch and said temperature
control switch is connected in parallel with said alarm.
18. The electric heater assembly of claim 16 further comprising
a temperature limit control switch including a sensing element,
said temperature limit control switch having a closed position in
which a short circuit is provided therethrough when said sensing
element senses the temperature of said heater to be below a predetermined
threshold value and having an open position in which an open circuit
is provided therethrough when said sensing element senses the temperature
of said heater to exceed said threshold value, wherein said temperature
limit control switch is connected in series with said tip-over switch
said series combination of said tip-over switch and said temperature
control switch is connected in parallel with said alarm.
19. The electric heater assembly of claim 18 wherein said heater
further includes a second heating element and means for selectively
short circuiting one of said heating elements.
20. An electric heater assembly comprising:
at least one electric heating element;
an electrically actuated alarm for providing an alarm warning upon
actuation;
a temperature control switch including a sensing element, said
temperature control switch having a closed position providing a
closed circuit therethrough when said sensing element senses the
temperature of said heater to be below a predetermined threshold
value and having an open position providing an open circuit therethrough
when said sensing element senses the temperature of said heater
to exceed said threshold value;
temperature control circuit means for electrically connecting said
heating element, said temperature control switch and said alarm
such that said temperature control switch disables said heating
element and actuates said alarm when said temperature control switch
is in said open position and such that said temperature control
switch enables said heating element and disables said alarm when
said temperature control switch is in said closed position;
wherein said temperature control circuit means comprises a temperature
control limit switch circuit wherein said alarm and said temperature
control switch are electrically connected in parallel and wherein
said parallel combination is connected in series with said electrical
heating element.
21. The heater assembly of claim 20 further comprising a heater
thermostat connected in series with and between said electrical
heating element and said parallel combination of said alarm and
said temperature limit control switch.
22. The heater assembly of claim 21 further comprising a tip-over
switch connected in series with and between said electrical heating
element and the parallel combination of said alarm and said temperature
limit control switch.
23. The electric heater of claim 20 wherein said alarm comprises
an electrically actuated audible alarm.
24. The electric heater of claim 22 wherein said alarm comprises
an electrically actuated audible alarm.
25. The electric heater of claim 24 wherein said alarm further
comprises an electrical pilot light connected in parallel with said
electrically actuated audible alarm.
26. The electric heater of claim 22 further comprising an electric
fan including an electric fan motor wherein said electric fan motor
is connected in series with and between said electric heating element
and said thermostat.
27. The electric heater of claim 22 including a second heating
element connected in series with said first heating element and
means for selectively short circuiting one of said electric heating
elements.
Description BACKGROUND OF THE INVENTION
This invention relates generally to electric resistance heaters
and more specifically to an abnormal condition detection system
for use in electrical resistance heaters, wherein the system will
automatically shut-off the heater upon detection of an abnormal
condition and simultaneously generate an alarm warning.
Safety considerations with regard to electric appliances and particularly
with regard to electrical resistance type space heaters have led
to the incorporation of various safety features in such heaters.
Two primary safety features which have been included in prior designs
are systems for effectively shutting off the electrical heater if
the temperature of the heating element exceeds a predetermined threshold
temperature and systems for shutting off the electric heater if
the electric heater is tipped over or tilted beyond a predetermined
upright or level position. These two safety features are desirable
since either of these conditions may constitute a serious safety
hazard if the heater is not effectively disabled upon the occurrence
of these events.
An example of an electric space heater safety system which includes
a gravity actuated tip-over switch is disclosed in U.S. Pat. No.
3,637,981 (Swimmer). The tip-over switch includes a weighted member
which maintains a vertical position resulting from the force of
gravity. An operating member attached to the weighted member urges
a pair of electrical contacts apart, thereby opening the circuit
for the heating element when the heater is tilted beyond a predetermined
angle.
U.S. Pat. Nos. 3,201,548 (Mertler) and 3,271,546 (Chesnut) each
disclose systems including a combined thermostat and tip-over switch
which may be used with electrical appliances such as with electrically
heated appliances. In the systems disclosed by these two references,
the appliance is de-energized by the separation of a single set
of electrical contacts. The systems include a gravity actuated pendulum
type tip-over switch to separate the electrical contacts when the
appliance is tilted beyond a predetermined level upright position.
The thermostat/tip-over switch also includes a set of bimetallic
blades which are responsive to temperature changes. The bimetallic
blades are used to separate the contacts when the temperature exceeds
a predetermined adjustable level.
Although the above described devices will effectively disable the
heating element of an electrical resistance type heater when the
heater is either tilted beyond a predetermined tilt angle or when
the heater exceeds a predetermined operating temperature, these
devices do not generally provide any indication to the user that
an abnormal condition has occurred. It is desirable to provide the
user with a warning signal in order for the user to take appropriate
steps to correct any hazardous condition which may arise due to
the abnormal operation of such heaters.
To this end, the arrangement disclosed in U.S. Pat. No. 4,755,653
(Townsend et al.) comprises a heater assembly which includes an
alert indicator. The alert indicator warns the user when the heater
either exceeds a predetermined safe operating temperature or is
tilted beyond a safe tilt angle. The alert indicator includes a
buzzer and a pilot light to provide a visual and aural warning to
the user when an abnormal condition has occurred. The buzzer and
pilot light are activated by a tip-over switch which is normally
in an open condition when the heater is in a normal upright level
position. When the heater is tilted, the tip-over switch closes
to activate the buzzer and pilot light. A thermostat which includes
a second tip-over switch is used to disable the heating element
when the heater is tilted beyond a predetermined level position.
The system also includes a temperature limit control which disables
the heating elements when the temperature exceeds a predetermined
temperature. The temperature limit control includes a single-pole,
double-throw switch with two sets of contacts. A first set of contacts,
normally in a closed position, enables the heating elements when
the heater is operating below the predetermined temperature. A second
set of contacts, normally in an open position, closes to activate
the buzzer and pilot light when the heater exceeds the predetermined
temperature.
Although the system disclosed by Townsend et al provides the desired
alarm warning, the system is not without limitations. Since the
system includes two separate tip-over switches, one to disengage
the heating elements and another to activate the alarm, any variance
between the settings of the two tip-over switches may reduce the
effectiveness of the alarm system. If the two tip-over switches
operate at different angles from one another, it is possible that
the heating elements may be disabled while the alarm system is not
actuated or that the alarm may be actuated without the heating element
being disabled. In either case, the effectiveness of the alarm system
is reduced. Further, it is desirable to minimize the number of tip-over
switches used in a heater for purposes of manufacturing economy.
It is therefore desirable to provide a system which includes an
alarm system wherein the alarm system will be actuated by the same
tip-over switch which disables the heating element. It is also desirable
to provide a system wherein the alarm will also be actuated by a
temperature limit control switch which disables the heating element
of the heater.
Therefore, in view of the above, it is a general object of the
present invention to provide a heater assembly wherein the same
tip-over switch disables the resistive heating element and actuates
an alarm system.
It is a further object of the present invention to provide a system
which requires only a single tip-over switch to disengage the heating
element and actuate an alarm system.
It is still a further object of the present invention to provide
a heater assembly wherein a temperature limit control switch disables
the heating element and simultaneously actuates an alarm system.
SUMMARY OF THE INVENTION
To achieve the foregoing and other objects and in accordance with
the purposes of the present invention, the heater assembly of the
present invention may include a heating element, an electrically
actuated alarm and a tip-over switch which provides a closed circuit
when the heater is in a predetermined level position and an open
circuit when the heater is tilted beyond a selected tilt angle.
The alarm, heating element and tip-over switch can be electrically
connected such that the tip-over switch disables the heating element
and actuates the alarm when the tip-over switch is in one of the
open and closed positions and such that the tip-over switch enables
the heating element and disables the alarm when the tip-over switch
is in the other of the open and closed positions.
In a preferred embodiment, the tip-over switch and the alarm are
electrically connected in parallel and the parallel combination
of the tip-over switch and the alarm are connected in series with
the electrical heating element.
Thus, the arrangement of the present invention provides a system
wherein the heating element is disabled by a tip-over switch which
provides an open circuit when the heater is tilted beyond a predetermined
tilt angle and wherein an alarm is automatically actuated when the
tip-over switch provides one of the open and closed circuits. The
system of the present invention does not require any further mechanical
process, such as the movement of a second tip-over switch or the
closure of an additional set of contacts, to actuate the alarm.
The arrangement of the present invention therefore provides a more
reliable system than systems which require further mechanical operations
to enable or actuate the alarm.
Additional objects, advantages and novel features of the invention
will be set forth in part in the description which follows, and
in part will become apparent to those skilled in the art upon examination
of the following or may be learned by practice of the invention.
The objects and advantages of the invention may be obtained by means
of the combinations which are particularly pointed out in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an electrical schematic representation of a first preferred
embodiment of the heating element assembly of the present invention.
FIG. 2 is an electrical schematic of a second preferred embodiment
of the heating element assembly of the present invention.
FIG. 3 is an electrical schematic of a third preferred embodiment
of the heating element assembly of the present invention.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
Referring now to the drawings, and specifically to FIG. 1, an electric
heater assembly 10 includes a heating element 26, an alarm 12 and
a tip-over switch 14. The heating element 26, alarm 12 and tip-over
switch 14 may be connected by any suitable electrical circuit (1)
which provides an arrangement wherein the tip-over switch 14 simultaneously
disables the heating element 26 and actuates the alarm 12 when the
heater is tilted beyond a predetermined angle and (2) which enables
the heating element 26 and disables the alarm 12 when the heater
is in a normal upright position. In the preferred embodiment illustrated,
the alarm 12 is electrically connected in parallel with the tip-over
switch 14 and the resistive heating element 26 is in turn connected
in series with the parallel combination of the tip-over switch 14
and the alarm 12. In this embodiment the tip-over switch 14 is disposed
such that it provides an open circuit therethrough when the heater
is tilted beyond a predetermined upright position and a short circuit
therethrough when the heater is in a normal level position.
When the heater is in a normal level or upright position the short
circuit provided by the tip-over switch 14 provides a direct electrical
path to the resistive heating element 26, such that the voltage
drop across the alarm 12 is substantially zero. When the heater
is tilted beyond the predetermined angle, the open circuit provided
by the tip-over switch 14 forces current in the circuit to pass
through the alarm 12, thereby actuating the alarm 12. As described
in more detail below the electrical resistance of the alarm 12 is
preferably several orders of magnitude greater than the electrical
resistance of the heating element 26. Therefore, when the alarm
12 is actuated, substantially all of the electric power in the circuit
will be dissipated by the alarm 12, thereby disabling the heating
element 26.
The alarm 12 may be any suitable means which provides the user
with a warning. Preferably, the alarm 12 includes an electrically
actuated audible alarm such as a coil type buzzer 20. The alarm
12 may further include a visual alarm means such as a pilot light
16. The pilot light 16 is preferably connected in series with a
resistor 18 to provide a sufficiently high resistance to disable
the heating element 26 when the alarm is actuated. Preferably the
buzzer 20 and the pilot light 16 are connected in parallel. For
reasons explained below, the buzzer 20 and pilot light 16 are preferably
of the type which fail in an open circuit condition.
A suitable buzzer 20 is available from U.S. Controls Corp. (New
Berlin, Wis.) as model No. 10189 which has a resistance of approximately
2.1K OHMS measured at the lead wires. A suitable pilot light 16
is a neon lamp available from several commercial sources. In an
exemplary embodiment the resistor 18 connected in series with the
pilot light 16 has a resistance of 30K OHMS.
The heater assembly 10 may include a temperature limit control
switch 22 having a temperature sensing element. The temperature
limit control switch 22 is preferably connected in series with the
tip-over switch 14 and the series combination of the tip-over switch
14 and the temperature limit control switch 22 is preferably connected
in parallel with the alarm means 12. In this preferred embodiment
the temperature limit control switch 22 provides a short circuit
therethrough when operating under normal conditions and provides
an open circuit therethrough when the sensing element of the temperature
limit control switch 22 detects that the temperature of the heater
assembly 10 has exceeded a predetermined safe operating temperature.
In a preferred embodiment the heater assembly 10 further includes
a thermostat 23 which is used to select the normal operating temperature
of the heater assembly 10. The thermostat 23 regulates the temperature
of the heater assembly 10 by disabling the heater element 26 at
a predetermined temperature. The thermostat 23 is preferably connected
such that one of the connecting terminals of the thermostat 23 is
electrically connected at the node between the tip-over switch 14
and the alarm 12. In this manner, cycling of the thermostat contacts
will not actuate the buzzer 20 or pilot light 16.
A suitable tip switch/thermostat is available as a single unit
from Norstat (Norwalk, Ohio), type SB509M or from Bimet (Morris,
Ill.). type TPS-22. These single unit tip switch/thermostat devices
include a mercury type tip-over switch and include an additional
connection point between the thermostat and tip-over switch. It
will be recognized by those skilled in the art that the tip-over
switch 14 and the thermostat 23 are available as individual components
from several commercial sources which are well suited for the purposes
of the present invention. A suitable temperature limit control switch
is available from Therm-O-Disc (Mansfield, Ohio).
A second heating element may be included to provide the user with
a range of operating temperatures for the heater assembly 10. In
the preferred embodiment of FIG. 1, a second heating element 28
is connected in series with the first heating element 26. A switch
30 which includes two contacts enables the user to selectively short
circuit the second heating element 28. When the lower heating element
28 is added to the heating element 26 a higher resistance is provided
thereby yielding a lower wattage at the same input voltage (preferably
of 120 volts AC). In this manner, the user can select whether the
heater is to be operated in a high mode of operation by short circuiting
the second resistive heating element 28 or whether the heater is
to be operated in a low mode of operation by connecting both the
resistive elements 26 and 28 in series.
In an exemplary embodiment, the resistive element 26 has a resistance
of 9.6 OHMS and the resistive heating element 28 has an electrically
resistance of 1.5 OHMS when measured at room temperature.
The heater assembly 10 may further include a fan including a fan
motor 24 to further enhance the heating capabilities of the heating
assembly 10. The fan motor 24 may be any suitable electric fan motor
and is preferably connected in series between the first heating
element 26 and the thermostat 23.
The heater assembly 10 may further include a second pilot light
32 which will provide a signal to indicate whenever the heater assembly
10 is in an "on" condition. This second pilot light 32
is preferably connected such that it always bypasses the tip-over
switch 14, temperature control switch 22 and alarm 12. In this manner,
the second pilot light 32 will indicate that the unit is in an "on"
condition independent of the state of the temperature limit control
22 or tip-over switch 14.
The heater assembly 10 may be connected to a power supply, such
as an AC power supply, by any suitable means and preferably by means
of a polarized plug 34.
FIG. 2 illustrates a second preferred embodiment of the present
invention wherein a heater assembly 110 includes an alarm 112 connected
in parallel with a tip-over switch 114 and wherein the parallel
combination of the tip-over switch 114 and the alarm 112 is connected
in series with a first resistive heating element 126. Similar to
the embodiment of FIG. 1, this preferred embodiment of FIG. 2 includes
a pilot light 116 connected in series with a resistor 118 and a
buzzer 120 which define the alarm 112.
A temperature limit control switch 122 which also provides an open
circuit when the temperature of the heating element 110 exceeds
a predetermined safe value is connected in series with the tip-over
switch 114 and in parallel with both the pilot light 116 and the
buzzer 120.
A thermostat 123 is provided between the tip-over switch 114 and
the heating element 126. Preferably, the tip-over switch 114 and
thermostat 123 are provided as a single unit with an additional
connection point between the thermostat and the tip-over switch.
Similarly to the arrangement of FIG. 1 this preferred embodiment
of FIG. 2 allows the tip-over switch 114 to perform both of the
functions of enabling or actuating the alarm 112 and disabling the
resistive heating element 126.
In the embodiment of FIG. 2, a four contact switch 130 is electrically
connected between the resistive element 126, a second resistive
element 128 the motor 124 of an electric fan. This arrangement allows
the user to selectively operate the heating elements of the heater
at a high mode of operation by selectively short circuiting the
second resistive heating element 128 or at a low mode of operation
by connecting both heating elements 126, 128 in series. This arrangement
also permits the user to operate the fan motor at either a high
setting when the heating elements 26, 28 are disabled or a low setting
when either heating element 28 is short circuited or when both heating
elements 26, 28 are connected. These various modes of operation
provide the user with a wide range of alternatives for the heater
settings.
Suitable resistive heating elements for the embodiment of FIG.
2 include a high heating element 126 with an electrical resistance
of 8.5 OHMS and a heating element 128 with an electrical resistance
of 1.4 OHMS when measured at room temperature. It will be recognized
by those skilled in the art that these are approximate resistances
and that any suitable resistance may be used depending on the use
contemplated.
The heater assembly 110 also includes suitable means such as a
polarized plug 134 for connecting the heater assembly 110 to a power
supply.
With the heater element assembly described with the preferred embodiments
of FIGS. 1 and 2, the tip-over switch will disable the heating elements
of the heater assembly when the heater is tipped or tilted beyond
a predetermined safe tilt angle. Similarly, the temperature limit
control switch disables the heating elements when the heating elements
exceed a predetermined threshold temperature. The temperature limit
control and tip-over switch are connected such that when an abnormal
condition exists the heating elements are disabled simultaneously
with the actuation the alarm. In the system of the present invention,
the tip-over switch and temperature limit control each serve two
functions. Thus, only a single tip-over switch is used both to disable
the heating element and to actuate the alarm. Similarly a single
temperature limit control switch is used to both disable the heating
element and actuate the alarm. With the arrangement of the present
invention the chances are minimized that when an abnormal condition
occurs the alarm will not be actuated or that the alarm will be
actuated without an abnormal condition occurring.
Since both the alarm pilot light and the buzzer are of the type
which fail with open circuits, the failure mode of these components
does not compromise the safety of the heating element by short circuiting
either the temperature limit control switch or the tip-over switch.
Since the alarm pilot light and the buzzer are preferably connected
in parallel, either one will function as intended independent of
whether the other one fails. The arrangement of the present invention,
thus, enhances the reliability of the alarm system without compromising
the system's abnormal condition shut-off capabilities.
Further, since a single tip-over switch is used to actuate the
alarm and disable the heating element, a more economical design
is provided those designs presently available in the art.
FIG. 3 illustrates another preferred embodiment of the present
invention. In the embodiment of FIG. 3, the temperature control
limit switch 222 is connected in parallel with the alarm 212. As
in the embodiments of FIGS. 1 and 2, the alarm 212 preferably includes
a pilot light 216 and a buzzer 220 connected in parallel with each
other. The temperature control limit switch 222 is preferably of
the type which provides an open circuit therethrough when the switch
222 senses that a predetermined temperature has been exceeded and
provides a closed circuit therethrough under normal operation. In
this embodiment the tip-over switch 214 is connected in series with
the parallel combination of the temperature control limit switch
222 and the alarm 212. The rest of the elements in this embodiment
are similar to the elements of the embodiment of FIG. 2.
The heater assembly 210 of this embodiment provides a more reliable
temperature control and alarm arrangement than presently available
arrangements. When the temperature control switch 222 senses that
the temperature has exceeded the preset temperature thereby providing
an open circuit, the alarm is automatically actuated by the opening
of the circuit and the heating elements 228, 226 are automatically
disabled. Unlike prior art designs there is no need for a switch
arm to close a set of contacts to actuate the alarm. Thus, the possibility
that the alarm will not be properly actuated if the switch arm malfunctions
is eliminated.
The foregoing description of the preferred embodiments of the present
invention has been presented for purposes of illustration and description.
These embodiments are not intended to be exhaustive, nor is it intended
to limit the invention to the precise forms disclosed in view of
the many modifications and variations that are possible in light
of the above teachings. The embodiments were chosen and described
in order to best explain the principles of the invention and its
practical applications, to thereby enable others skilled in the
art to best utilize the invention in various embodiments and with
various modifications as are suited to the particular use contemplated.
It is intended that the scope of the invention be defined by the
following claims, including all equivalents. |