Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to an alarm apparatus for a
freezer, and it more partlcularly relates to an alarm
apparatus suitable for a domestic freezer.
At the present time, many households have a
freezer, for storage of a variety of food. The freezers have
the advantage of enabling a wide variety of food products to
be stored for a long time. However, if the freezer fails,
this can lead to the food being spoiled. Consequently, if a
failure is not detected sufficiently early, then the entire
contents of the freezer will become defrosted and will have
to be disposed of.
This problem is compounded by the fact that
freezers are often located in a relatively little used part
of the house, so that a freezer failure can go undetected
for some time. This problem is particularly acute, when one
leaves the house empty for a weekend or longer, for a
vacation etc. Typically, people overlook the necessity of
maintaining a watch on the freezer whilst on vacation. Even
if arrangements are made for someone to oversee the house,
often that person will not think to check the freezer at
regular intervals. Consequently, again a freezer failure can
go undetected for some time.
Accordingly, it is desirable to provide an alarm
apparatus, which will provide a clear warning of failure of
a freezer. Such an apparatus should not require any
modification of the freezer. Further, it should enable a
clear indication of a freezer failure to be given to someone
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outside the house.
In accordance with the present invention, there is
provided an alarm apparatus, for a freezer having a body and
a closure member, the alarm apparatus comprising an
electrical control unit including a power supply input, an
alarm device connected to the control unit, a temperature
sensor connected to the control unit, which temperature
sensor is adapted for mounting in a freezer, for detecting
temperatures exceeding a pre-set temperature, and a first,
flexible lead connecting two of the control unit, the alarm
device and the temperature sensor together, the first lead
having a cross-section enabling the lead to extend between
the body and the closure member of the freezer whilst
permitting closure thereof.
The control unit can be located either outside or
inside the freezer, but it is preferred for the control unit
to be located outside the freezer. With the control unit
outside, it can readily be connected to a conventional A.C.
socket. A control unit located within the freezer could not
so readily be connected to an electrical socket, and may
have to rely on a battery as a source of power. The control
unit can have a 9 volt D.C. input. In this case, a second
lead would be provided for connecting the control unit to a
transformer, for connection to a standard domestic A.C.
socket.
Further, although the control unit and the alarm
device can be mounted together, it is preferred in many
1;~0;~6~1~
cases to have them mounted separately. Thus, the alarm
device can be connected to the control unit by a third lead.
Connection of the various components together by appropriate
leads enables the apparatus to be readily fitted. For most
installations, it should be sufficient to provide standard
size leads of sufficient length to enable the user to
arrange the components as desired.
For a better understanding of the present
invention, and to show more clearly how it may be carried
into effect, reference will now be made, by way of example,
to the accompanying drawings, which show a preferred
embodiment of the present invention, and in which:
Figure 1 is a perspective view of an alarm
apparatus according to the present invention, shown fitted
in a freezer;
Figure 2 shows a circuit diagram of the control
unit;
Figure 3 shows a vertical, sectional view of the
control unit; and
Figure 4 shows an end view of the control unit.
With reference to Figure 1, the appara-tus as a
whole is denoted by the reference 1. The apparatus 1 has a
control unit 2, a sensor 3, and an alarm or warning light 4.
Further, a transformer 5 is provided for the control unit 2.
The sensor 3 is shown mounted in a freezer, shown
at 6. The freezer 6 includes a body 8 and a lid 10. The lid
10 is the closure member of the freezer 6, and in other
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freezer designs would be formed as a door. Conventionally,
at the present time, such a lid 10 has a sealing strip,
which has a certain degree of resilience.
A first lead 12 extends between the sensor 3 and
the control unit 2. As shown, in known manner, the freezer 6
includes a wire basket 14. To locate the sensor 3, part of
the lead 12 is wrapped around the basket 14. The first lead
12 includes two conductors, and is of small cross-section.
This enables the lead 12 to extend between the lid 10 and
body 8, when the freezer 6 is closed; the seal of the lid 10
deforms sufficiently J to maintain a good seal.
The sensor 3 is integral with the lead 12. The
other end of the lead 12 is provided with a plug 16, for
plugging it into the control unit 2.
Similarly, the transformer 5 is provided with a
second lead 18, including a plug 20 at one end thereofO The
plug 20 again is plugged into the control unit 2. The
warning light 4 is connected to a third lead 22, which
includes a respective third plug 24.
The transformer 5 can be a conventional
transformer for converting a household A.C. supply to a 9
volt D.C. supply. It should be capable of accepting 117
volts A.C. at 60 HZ at the input, whilst delivering a 9 volt
D.C. output at 200 MA. It should preferably be UL and CSA
approved.
The warning light 4 is a light emitting diode
(LED).
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Turning to the control unit 2, the arrangement of
the components in the control unit 2 i5 shown in Figures 3
and 4. It is to be appreciated that this arrangement is
merely preferred, and that the size of the body and the
arrangement of the components can be varied, without
effecting operation of it.
The control unit 2 has a housing 30, which is a
generally rectangular prism. The housing 30 includes a front
wall 32 provided with a number of perforations 34, for an
audible alarm. It also includes two openings 36, for the two
LED's. A bottom wall 38 includes openings 40, for connection
sockets. As shown in Figure 3, a partition 42 separates a
battery compartment 44, from the rest of the interior of the
housing 30. A plastic cover plate 46 covers off the rear of
the housing 30.
Within th~e housing 30, a piezo electric alarm 48
is mounted on standoffs 50 adjacent the perforations 34, for
producing an audible alarm. The piezo alarm 48 also serves
as a support for a printed circuit board 52.
As shown in Figure 5, in the openings 40 in the
bottom wall 38, there are three sockets. A first socket 54
is provided for the plug 16 for the sensor 3. Corresponding
second and third sockets 56, 58 are provided for the second
and third plugs 20, 24.
Turning to the circuit diagram of Figure 2, the
second socket 56, for the power supply, has its negative
side connected to a common negative line 71. The positive
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side of the socket 56 is connected through a diode 64 to a
positive line 70. There is also a connection between the
positive and negative inputs of the socket 56 through a
second light emitting diode 60 and a first resistor 62 in
series. The second light emitting diode 60 is located in the
left hand aperture 36 as viewed in Figure 1.
As shown at 57, a battery supply connection is
connected to the positive line 70. A negative battery
connection (not shown) is connected directly to the line 71,
whilst the positive connection is through a diode 68. The
positive line 70 is connected through a second resistor 66
to the first socket 54 for the sensor 3.
An integrated circuit operational amplifier 72 is
connected to the positive and negative lines 70, 71 as
shown. It also has an input 74 connected to the junction
between the second resistor 66 and the socket 54, so that
the voltage generated across the sensor 3 is input to the
operational amplifier 72.
A third resistor 76 is connnected in series with a
variable resistor 78 and a fourth resistor 80, between the
positive and negative lines 70, 71. A zener diode 81 is
connected and parallel across the two resistors 78, 80. An
input line 82 is connected between the operational amplifier
72 and the variable resistor 78 as shown. This enables the
operational amplifier 72 to act as a comparator, which
compares the fixed voltage generated at the variable
resistor 78 by the zener diode 81, to the voltage across the
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sensor 3.
An output of the operational amplifier 72 is connected
via fifth and sixth resistors 84, 86 to the negative line 71, with
the base of a transistor 88 connected to the junction between the
two resistors 84, 86.
A third light emitting diode 90 and a seventh resistor 92
are connected in series between the positive line 70 and the
collector of the transistor 88. The third light emitting diode 90
i~ located in the right hand aperture 36 of the housing 30, shown
in Figure 1.
Lines 94 provide a connection to a timer circuit
including an LM555 integrated circuit 96. This is connected to
resistors 98, 100 and 102 and a capacitor 104 in known manner.
The third, output socket 58 has three output pins 58a,
58b and 58c. 58a is a common terminal that is connected to the
positive line 70. Terminal 58b provides a fixed or continuous
output, which can be used if desired, possibly in conjunction with
a buzzer, warning light 4 or other alarm that optionally includes
its own timer or intermittent circuit. Terminal 58c provides an
intermittent output, determined by the timer circuit 96 and can be
connected to the light 4 or other alarm device, to provide an
intermittent audible or visual alarm.
The timer circuit enables a simple piezo electric alarm
48 to be used, whilst still having an intermittent output. The
alarm 48 is effectively connected across the terminals 58a, 58c, to
provide it with an intermittent output. Where an intermittent
output is not desired, or the alarm device includes its own
intermittent circuit, the timer circuit could be eliminated and a
two terminal socket
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connected to lines 58.
In use, the apparatus l is mounted as shown in
Figure l. The sensor 3 is located within the freezer 6,
either with the lead 12 wrapped around the wire basket 14,
or unwrapped. The transformer 5 is connected to the control
unit 2 and plugged into a standard socket. The warning light
4 is placed at a suitable location, where it can be seen,
and connected to the control unit 2. The control unit 2
itself is mounted at any suitable location adjacent the
freezer 6. When powered, the second light emitting diode 60
is illuminated, giving an indication that the apparatus is
in operation.
The apparatus l then monitors the temperature in
the freezer 6. This is achieved by comparing the output of
the sensor 3 with the voltage on the input line 82. If the
voltage of the sensor 3 equals or exceeds the fixed voltage
on line 82, then the output of the operational amplifier 72
goes to 9 volts. This turns on the transistor 88, which in
turn turns on the piezo electric alarm 48. The alarm 48
gives an audible alarm. Simultaneously, the third light
emitting diode 90 on the front of the control unit 2 is
turned on.
Thus, the control unit 2 by itself provides both
an audible and a visual alarm. However, the output socket 58
is provided, so that an additional alarm or warning can be
given remote from the control unit 2. The ouiput at socket
58 is 9 volts when activated. As shown, this is connected to
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the first light emi-tting diode of the warning light 4, to
give a visual warning, which will be pulsed or constant
depending on which socket 58b, 58c is used. Alternatively,
this socket 58 could be connected to another alarm device or
to a 9 volt relay, which turns on a 120 volt A.C. outlet.
The warning light 4 can be placed at any suitable
location. For example, it is common when a householder goes
on vacation to arrange for a neighbour to maintain a watch
on the house. In this case, the warning light 4 could be
placed in a basement window, or other window adiacent the
freezer. Then, if the freezer fails, the light will be
illuminated, and the neighbour will be given a warning,
without having to enter the house. Appropriate action can
then be taken.
The battery connection 57 is provided solely as a
backup to the main power supply. One of the principal
sources of failure of the freezer is failure of the
electrical supply. Accordingly, if this occurs, the
apparatus 1 should still be active. Preferrably, a 9 volt
alkaline battery is used. Then, a warning will be given, if
the power supply fails. This also serves to keep the
apparatus 1 active, even if the user accidentally forgets to
plug in the transformer 5.
To test if the apparatus 1 is working correctly,
one can simply remove the sensor 3 from the freezer 6. The
sensor 3 is then allowed to warm up sufficiently to switch
on the apparatus. One can then check that the warning lights
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4, 90 and the pie~o electric al~rm 48 are Eunctioning
correc-tly.
The various components of the apparatus can be
compact. This makes the apparatus 1 easy to install and
transfer from one freezer to another. The sensor 3 can be
quite compact, and take up little space in the freezer.
By way of example, in the following table, a list
is given of suggested components for the apparatus:
TABLE 1
PARTS LIST FOR FREEZER ALARM
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Diode 64: IN4004 DIODE
Diode 68: IN4004 DIODE
Zener diode 81: IN4733 51 V ZENER DIODE
Operational Amplifier 72: LM741 OP.AMP.
Temperature sensor 3: LM335Z TEMPERATURE SENSOR
Integrated circuit 96 LM555 TIMER
Transistor 88: 2N2222 A NPN TRANSISTOR
1st Resistor 62: 470 OHM 1/4 W. 5%
2nd Resistor 66: 5.6K OHM 1/4 W. 5%
3rd Resistor 76: lK OHM 1/4 W. 5%
4th Resistor 80: lK OHM 1/4 W. 5%
5th Resistor 84: 12K OHM 1/4 W. 5%
6th Resistor 86: 3.9K OHM 1/4 W. 5%
7th Resistor 92: 220 OHM 1/4 W. 5%
8th Resistor 98: 2.2M OHM 1/4 W. 5~
9th Resistor 100: 2.2M OHM 1/4 W. 5%
10th Resistor 102: 470 OHM 1/4 W. 5%
Variable Resistor 78: lK OHM 3/4 W. 15 TURN POT
Transformer 5: 9 V. D.C. 200 MA. O/P 117
VAC-60 HZ l/P WITH 5.5 m/m
POLARIZED PLUG
Socket 54: 3/32 JACK 2 CONDUCTOR SUB-MINI-
Socket 56: 5.5 m/m X 2.1 m/m JACK
Socket 58: 1/8 JACK 3 CONDUCTOR MINI
First LED 3: RED Tl 3/4 FLASHING
Second LED 6: RED Tl 3/4
Third LED 90: GREEN Tl 3/4
