GB2031631A

GB2031631A - Refrigerator temperature monitor

Info

Publication number: GB2031631A
Application number: GB7840764A
Authority: GB
Original assignee: SHEW A
Current assignee: SHEW A
Priority date: 1978-10-16
Filing date: 1978-10-16
Publication date: 1980-04-23

Abstract

Means for monitoring the operation of a refrigerator or cold room or freezer comprises a temperature sensing device (1) for location in the cold compartment of the refrigerator and connected to an alarm circuit for indicating, by an alarm (6), a preset high temperature, and a circuit which is responsive to the energising of a defrosting electrical heater (7) in the refrigerator and which includes a time delay (4) which is activated by operation of said heater (1) so as to deactivate said alarm for a preset period after activation of the defrosting heater (1). The refrigerator failure alarm is thus not activated during defrosting periods. <IMAGE>

Description

SPECIFICATION Refrigerator monitoring means This invention relates to refrigerator monitoring means including alarms to provide warning of failure in refrigeration equipment.

Faults can occur for mamf reasons and tnege include power failure, meci-,anical or electricai i,reak- down, overloading by the user, blocked drains or maladjustment, to mention but a few.

Methods based on sensing the temperature in the refrigeration equipment are preferred but have not been very successful because of the usual arrangements to automatically melt away unwanted build up of water and water vapour from the refrigerator mechanism. These defrost arrangements usually take the form of either electrical heaters positioned to melt the accumulated ice under the control of a time switch providing typically two to four heating periods every 24 hours. Or alternatively, time switches controiling the circulation of hot gases derived from other parts of the system through the evaporator are provided.

These methods result in rise in temperature of the refrigerator environment making a simple sensing system impractical. The rise in temperature is of short duration so as not to damage the produce stored in the refrigerator but is adequate to melt the build up of ice which drains away to waste.

It is, accordingly, the object of the present invention to provide an equipment which overcomes the above disadvantages and limitations.

According to this invention there is provided refrigerator monitoring means comprising a temperature sensing device connected to an alarm circuit and a disabling circuit therefor responsive to the energising of the refrigerator defrost heater which circuit includes a time delay means.

Further features of the invention provide for a plurality of sensing devices and associated disabling circuits to be connected through a single alarm circuit.

The alarm circuit may be connected to a further remote point or points by conventional wiring, a telephone dialling or by radio.

The invention also provides for the delay means to include the normal time switch used to control the refrigerator defrost period and a second timer to extend the operation of the disabling circuit for a period to allow the refrigerator to recover normal low temperature.

The invention will now be described by way of an example with reference to the accompanying drawing which shows in block form the operation of an alarm for two refrigerators. This illustrates how the apparatus may be connected to a plurality of refrigerators and share a common alarm.

1 represents temperature sensitive resistors located in the refrigerator environments and lamps 2 indicate which circuit is indicating an alarm condition. The outputs from the temperature sensing resistors are applied to voltage comparators 3 which are also connected to the outputs from delay timers 4.

The outputs from the comparators 3 are connected to a common audible alarm 5 through isolating diodes 6.

In parallel with a defrost heater element 7 for each refrigerator unit is means for energising the time delayed disabling circuit. In one form this means consists of a transformer 8 the primary coil of which is in parallel with the element 7. In the alternative form illustrated a relay coil 9 is connected in parallel to the defrost heater elements 7 and 10 and indicates the normally open contacts of the relay.

The apparatus operates in the following manner.

Assume a refrigerator is adjusted using its normal controls to maintain a refrigerated space at -200C and an alarm signal is required should the space temperature rise to -10 C at any time other than that caused by defrost, The voltage comparator 3 is adjusted so that its output goes high when the temperature at its sensor 1 exceeds this figure.

Normally the output would be low at temperatures lower than -10"C.

Whep the comparator output goes 'high', alarm 5 is sounded and the appropriate signal lamp 2 is illuminated. Diodes 7 isolate feeds to the remaining lamp.

The 'high' signal at the output of voltage comparator 3 energises a relay 11 to cause contacts 12 to initiate a remote alarm, a telephone dialler or a radio transmitter to warn of a refrigeration fault when such additional alarm means are included in the system.

Timer 4 is initiated by a voltage on its trigger terminal 13, derived from transformer 8 with its primary in parallel with defrost heater element 7 when the latter is energised.

In the alternative method, timer 1 requires its trigger terminal 14 to be grounded to initiate timing.

This is achieved by connecting relay coil 9 in parallel with defrost heater 7 and connecting normally open contact 10 between terminal 14 and ground.

Where convenient, the transformer 8 and relay coil 9 may be connected directly to the time switch or its contactor normally provided to control the defrost function instead of being wired across the heater.

The timers 4 are set to such a value as to allow the refrigeratortimeto recover after a defrost period.

The timers are variable and a convenienttiming cycle has been found to be 90 minutes if nuisance alarms are to be avoided.

The timer output X and Y are complementary.

During non-timing periods the output at X is high and the output of Y low. On receipt of a trigger signal at terminal 13 to initiate the timer, the two outputs X and Y change state, X goes low and Y goes high.

The low output at X connected to the negative input of the comparator 3 drives the output of 3 low independent of the temperature in the refrigerator and thereby preventing an alarm signal.

By going high at Y, a lamp 15 is energised indicating defrost in progress.

The system includes means for indicating the temperature in any refrigerator whetherthe fixture or cold room is on defrost or not. It is thus possible to monitor the temperature at any time. Change over switches 16 are drawn in the normal alarm connected position. On changing to the alternative position sensors 1 are connected to indicator 17.

The system is preferably DC battery operated from an accumulator maintained in a fully charged condition from a mains driven power supply pack, thereby providing protection in the event of power failure.

Claims

1. Means for monitoring the operation of a refrigerator or cold room or freezer, which comprises a temperature sensing device for location in the cold compartment of the refrigerator and connected to an alarm circuit for indicating a preset high temperature, and a circuit which is responsive to the energising of a defrosting electricai heater in the refrigerator and which circuit includes a time delay means which is activated by operation of said heater so as to disactivate said alarm means for a preset period after activation of the defrosting heater.

2. Means as claimed in Claim 1, wherein the means for activating said delay means comprises a transformer of which the primary coil is in parallel with each defrost heater element.

3. Means as claimed in Claim 1, wherein the means for activating said delay means comprises a relay coil connected in parallel to the defrost heater elements.

4. Means as claimed in Claim 1,2 or 3, wherein the temperature sensing device comprises a temperature-sensitive resistor, the output from which is connected to a voltage comparator connected to an alarm device and also the ouput from said time delay means.

5. Means for monitoring the operation of a refrigerator, freezer or cold room, substantially as hereinbefore described with reference to or as shown in the accompanying drawing.