GB2175117A - Alarm for open port - Google Patents

Abstract

This invention provides an alarm-producing device for the indication of the leaving of a port of an enclosure, such as a refrigerator door or the door of a room, open for longer than a predetermined time period, which said alarm device comprises a source-detector means, a delay means, an alarm means, a reset means, and a power-supply means, and optionally includes amplifier means for alarm means, source means, attachment means, and alarm-disabling means. Said alarm device may be integral to the enclosure, or may be a separate unit attached by attachment means to said enclosure. Said source means may be part of the enclosure, e.g., the light-power-source means in a refrigerator, or it may be a separate source, e.g., the ambient light outside of a refrigerator. When said outside ambient source means is weak, an amplifier means is provided. Included in this invention are intrusion detectors and insulation-testing devices. <IMAGE>

Description

SPECIFICATION Alarm for open port The present invention relates to alarms to indicate the opening of a port, especially the door of a refrigerator for more than the predetermined delay period.

The inadvertent leaving of a refrigerator door open is a common occurrence, and especially among the elderly. Such negligence leads to spoiied food, greater energy bills, unnecessary refrigerator wear and tear, and general annoyance. However, there is no mention of a device for indicating that a refrigerator door has been left open for longer than a given maximum allowed period in the Art.

Therefore, this invention proposes a means of indicating the leaving of a port, such as a refrigerator door open for longer than the predetermined delay period.

In general, the invention comprises a source means, controlled by the position of the port (open or closed); a source detector; a delay means; an alarm means; a power supply means; and, a reset means. Said source means may be, when the said port is the refrigerator door, the electric current allowed to flow to the refrigerator bulb when the door is opened, may be the removal of a magnet attached to the door, said removal deactivating a reed relay; may be the ambient light outside of the refrigerator; or, may be the said refrigerator light bulb itself. Said detector may, in the case of the source means being the refrigerator bulb, be an LDR, etc. Said delay means might be an RC circuit; said reset means might then be a means for discharging the capacitor member of said RC circuit.

When the source means is the electric current supplied when the refrigerator door is opened, the said alarm device would preferably be an integral part of the refigerator. On the other hand, when using the refrigerator light as the source, said alarm device would be a separate unit, including attachment means for attachment to the refrigerator.

When the outside ambient light is the source, the alarm device of this invention might be either a separate or integral unit.

Said attachment means for the separate unit might be a screw which could be fastened to one of the refrigerator grill grooves; the LDR position vs. the light source might be altered to vary the said delay time somewhat when the internal indicator lamp is the light source.

Or, a magnet within the separate alarm device unit could hold the device to the inside of the refrigerator.

When the door is intentionally opened for a relatively long period, the alarms may be disabled by covering the LDR with a covering means; by shorting the amplifier base to emitter, as shown below, using a shorting means; etc.

Brief description of the drawings Figure 1 General invention principle.

Figure 2 Alarm device using indicator light power as source.

Figure 3 LDR amplifiers for outside ambient light source.

Description of the preferred embodiments Fig. 1 is a block diagram of the general invention principle. The source 1 is activated (or, in the case of a magnet/reed relay, deactivated) by the opening of the port, e.g., a refrigerator door. Detector 2 receives the signal from the source 1, and after a delay period determined by delay means 3, e.g., 30 secs, enables alarm means 4, which includes amplifying means to amplify the signal from the detector 2, if necessary. When the port, e.g., a refrigerator door is once again closed, reset means 5 turns off the alarm 4 in a reasonable time.

Figs. 2a and 2b show embodiments of the invention where the detector means 2 is a phototransducer such as an LDR powered by the indicator light power source.

Fig. 2a shows the separate unit used with the indicator light. When the refrigerator door (not shown) is opened, the refrigerator light source 20 is enabled by the N.C. door switch 9, and lowers the resistance of the LDR to a relatively low value. Current from d.c. source 7 (e.g., a 9-volt battery) flows in a constant amount via limiting resistor 3a, which is also the timing resistor, to timing capacitor 3.

When the voltage across timing capacitor 3 reaches the proper value to turn on alarmmeans amplifier transistor 4a, which may be a Darlington transistor, sound transducer means 4 (e.g., a buzzer) turns on, signalling the prolonged door opening. Capacitor 6 improves buzzer sound quality. Resistance 5 will reset the timing capacitor, once the door is closed, in a reasonable time.

Switch 8 turns off the amplifier transistor 4a, by shorting the latter's base and emitter when in closed position.

Fig. 2b shows the unit integral with the refrigerator, according to this invention, powered, when N.C. door switch 9 is released, by the mains voltage appearing across the indicator bulb terminals, which said voltage is lowered by the transformer-less ballast capacitor 10, the action of which latter is described and claimed in copending Application No. XXXXX.

Besides components 11, 12, 13, 14a and 14b, this alarm is identical to that of Fig. 2a, except for the deletion of LDR 2, which, of course, is unnecessary here.

Fig. 3 describes amplifiers for the phototransducer, e.g., an LDR, as in the alarm of Fig. 2a, necessary when an alarm which will work under most circumstances is desired, even when the port, e.g., a refrigerator door is open to such a small extent that the door switch remains closed, so that the indicator lamp terminals remain unpowered. They thus can be independent of the refrigerator lamp, being enabled even by the outside ambient light which enters the slightly opened door, unless said light is extremely weak. Obviously, if the refrigerator light is enabled by opening the door, it will be of more-than-enough intensity to activate the alarm, after the usual delay period, when using these amplifiers. Thus, the LDR need not be placed opposite the said indicator lamp.On the contrary, it should be placed as close as possible to the door opening, at the angle proper to receive maximum light from the outside. Obviously, such an LDR amplifying device could be used for either a separate, or integral alarm unit.

Since the amount of light that will be available is unknown, and variable, in these embodiments, a constant-current source must be triggered when said light becomes available, after a certain threshold of light is reached.

Thus these embodiments have in common a constant-current source resistor 3a, sourcing current when the light impinging on LDR 2 exceeds the threshold, by turning on the threshold detecting means: transistor 15 in Fig. 3a; regenerative switch 15a-15b in Fig.

3b; and, op. amp. 15 in Fig. 3c, respectively.

A battery, the power supply of Fig. 2b, a rectified transformer voltage, etc. may be used to power these embodiments, where applicable.

The embodiments of Figs. 3b-c are abrupt, in that they remain off up to the threshold, while that of Fig. 3a allows a small current to flow into the amplifier 4a base even before the threshold point. One controlling factor in these embodiments is that the resistance of the LDR in very-low ambient light (with the door open only slightly) must be less than the LDR resistance when the door is closed in bright ambient daylight. The opposite can be true if the light can "leak' through the door padding.

For example, the measured (equilibrium) resistance of an LDR within a closed refrigerator in a darkened room, when the only light source was the street lighting coming through the room's windows at night was no less than 250 Mohms. Upon opening the refrigerator door somewhat, the resistance dropped to about 80 Mohms. Thus, the indicated said light threshold could in this case be that giving an LDR resistance of about 100-150 Mohms. Such very sensitive light alarms of Fig. 3 can be the basis of an intrusion detector. In this case, the time constant 3-3a could be reduced, as desired.

Said alarms could also be the basis of an insulation tester. Thus, an almost instantaneous insulation test could be made, without the need to measure any other variable (change).

(The time constant would be small for this embodiment.) The above Figures are exemplary only, and should not be taken to limit the scope of the invention. It should also be understood that the alarm devices of this invention can be used in many cases for other enclosures bounded by one or more ports, e.g., a room having one or more doors, and that the LDR mentioned may in many cases be replaced by a different phototransducer, e.g., a phototransistor or photo-SCR, in which case the phototransducer and its amplifying means are in a single unit, for use in possible very-low ambient light conditions, as mentioned. The said abrupt phototransducer amplifying means may be other than those mentioned above, e.g., a Schmitt trigger, etc.

Claims (18)

1. An alarm device for indicating that a port of an enclosure is left open for longer than a predetermined time delay period comprising: a source detector means; a delay means; an alarm means, optionally including amplifier means; a reset means; a power supply means; optionally, a source means; optionally, an attachment means; and, optionally, an alarm disabling means.

2. An alarm device as in claim 1 where said port is a refrigerator door and where said delay time is sufficient to allow usual opening in ordinary conditions without enabling the alarm, and where said alarm is enabled when said door is opened for more than the delay period.

3. A refrigerator alarm as in claim 2 where said source means is the refrigerator indicatorlight power controlled by the refrigerator door switch position, and where the said alarm device is integral with the refrigerator.

4. A refrigerator alarm as in claim 2 where said source means is the refrigerator light itself controlled by the refrigerator door position, where said detector means is a phototransducer, and where the said alarm device is a separate unit.

5. A refrigerator alarm as in claim 2 where said source means is a suitable permanent magnet and said detector means is a reed relay, one of which is set on the refrigerator door, while the other is set in opposite attitude on the front body of the refrigerator, where the opening of the door releases said reed relay, causing a signal to occur, which, after the delay caused by the said delay means enables the said alarm means, and where said alarm device is integral with the refrigerator.

6. An alarm device as in claim 1 where said source means is the outside ambient light, where said detector means is a phototransducer equipped with phototransducer amplifying means whereby under lowest ambient light conditions with the port slightly open said phototransducer conductance is greater than that when the port is closed in bright ambient light, and enough to enable alarm means after said delay period passes, and where said alarm device may be either a separate unit, or may be integral with the enclosure.

7. An alarm device as in claim 6 where said phototransducer amplifying means is chosen from the group comprising: non-abrupt means, such as a transistor; and, abrupt means, such as a regenerative switch or operational amplifier.

8. An alarm device as in claim 6 where said phototransducer is an LDR or similar with a resistance of 100-150 Mohms or lower under open-port conditions, before amplification by said phototransducer amplifying means.

9. An alarm device as in claim 6 which is an intrusion detector.

10. An alarm device as in claim 6 which is an insulation detector giving an alarm when insulation of the periphery of an enclosure is insufficient to keep out light quanta of sufficient amount to enable alarm.

11. An alarm device as in claim 4 or 6 where said phototransducer means is an LDR.

12. An alarm device as in claim 1 where all said means are integral to the enclosure.

13. An alarm device as in claim 1 wherein said device is attached as a separate unit to the body of the enclosure by attachment means.

14. A separate device as in claim 13 wherein said attachment means is either a screw or a magnet.

15. An alarm disabling means as in claim 4 or 6 chosen from: a covering means which can cover the phototransducer; and, a shorting means for the input of the said alarm-means amplifier or of the said phototransducer amplifier.

16. A separate alarm device unit comprising: an LDR source-detector means with optional aiflplifying means; an RC delay means; a buzzer alarm means; a transistor alarm amplifier means; an electric battery; and, a resistance means shunting said capacitor of said RC means, whereby the presence of a light source for more than the delay period will activate the said buzzer.

17. An intrusion detector as in claim 9 where said port is a room door.

18. An alarm device unit substantially as described herein with reference to Figs. 1, 2 or 3.