AU725153B2 - Timer with resettable alarm and automatic turn-off - Google Patents

Description

WO 99/24998 PCT/AU98/00901 1 TIMER WITH RESETTABLE ALARM AND AUTOMATIC

TURN-OFF

This invention relates to an appliance timer incorporating: timing means for automatically turning off the power to an electrical appliance after a set or selected period of time; alerting means to warn of an impending disconnection of power to the appliance through the action of the first said timer as the set or selected period of time is approached and or reached; resetting means to re-start the timing and alerting sequence if the appliance is required to operate or remain in use for a period of time exceeding the timer time-out period; and silencing means to mute the emitted warning so that the appliance may continue to operate or be used until the timer times out without interference by the emitted warning. This facility is useful if the timer is to be allowed to time out without any extension of time.

BACKGROUND OF THE INVENTION AND PRIOR ART.

Duration timers are widely used to control all types of appliances and are commonly found in the home where they form an integral part of appliances such as microwave ovens, conventional ovens, and room heaters. These timers in the main are of two distinct types, namely: "Duration of use" timers designed to turn off an appliance at the end of a set or selected period of time and are found in appliances such as domestic microwave ovens and room heaters.

WO 99/24998 PCT/AU98/00901 2 The end of the timing period is sometimes signalled by an audible and or visual device to alert the user of the completion of the timing sequence, the audible and or visual signal being one of short duration.

The difficulty associated with "duration of use" timers is that it may be some time before the user realises that the appliance has been turned off as would be the case if the user was distracted by a caller at the door, an incoming telephone call or by any other task at hand.

Therefore if the appliance is required to be used for a period of time longer than originally intended to achieve a desired result, the process may be interrupted for a considerable period of time before it is restarted. As some processes, cooking included, sometimes cannot yield the desired outcome if interrupted for a long period of time, it is realised that "duration of use" timers can have considerable limitations in their applications.

It is to be noted that the audible and or visual alert signal associated with "duration of use" timers is normally of short duration and therefore can very easily result in the signal being missed altogether if the user is not in the immediate vicinity of the appliance when the timer times out when the short duration alert signal is produced.

"Alerting" timers designed to alert the user of an appliance at the end of a selected period of time and are normally found in appliances such as conventional ovens. The audible and or visual signal is provided as an alert only and the appliance remains operational until manually turned off.

The disadvantage of "Alerting timers is that they do not turn appliances off so that when appliances incorporating such timers are WO 99/24998 PCT/AU98/00901 3 used or operated by an aged person or by a person who is forgetful by nature, potentially dangerous situations may arise. A typical example is a conventional oven which when left unattended for some time as would be the case if, for example, the operator is distracted by an incoming telephone call, can cause a,house fire.

It is therefore the object of this invention to provide a timer which overcomes the shortcomings and limitations of the previously mentioned "duration of use" and "alerting" timers. Such a timer incorporates means for automatically turning off the power to an electrical appliance after a set or selected period of time; alerting means to warn of an impending disconnection of power to the appliance; resetting means to re-start the timing and alerting sequence if the appliance is required to operate or remain in use for a period of time exceeding the timer time-out period; and silencing means to mute the emitted warning so that the appliance may continue to operate or be used until the timer times out without interference by the emitted warning. This facility is useful if the timer is to be allowed to time out without any extension of the time originally set or selected.

An embodiment of the invention is described in the following subsections of this specification and is as illustrated by the accompanying drawing. The drawing, however, is merely illustrative of how the invention might be put into effect and is not to be understood as being limiting on the invention.

FIG. I shows the connection of the active (live) and neutral conductors of a low voltage mains supply to the primary winding of a transformer, on one side, and to an electrical appliance on the other, the latter connection being through a set of normally open double pole single throw relay contacts.

WO 99/24998 PCT/AU98/00901 4 When switch S1 is closed, the secondary of the transformer and its associated bridge rectifier circuit consisting of Diodes D4, D5, D6 and D7 provide an extra low DC voltage across capacitor C1 for the purpose of energising the control circuit whose operation is as follows: (1)Through operation of the momentary action normally open switch S2, capacitors C3 and C2 are very quickly charged to the full supply extra low DC voltage present across capacitor C1 by current flow through resistor R1, diode D3 and diode D2. The charged capacitors C3 and C2 thus provide the full available extra low voltage to the gates of both FET transistors TRI and TR2 to turn them fully on. The relay coil connected to the drain of FET TRI is energised to close the relay contacts in series with the electrical appliance which operates. Similarly, conduction of transistor TR2 causes the voltage at point P connected to the gate of FET transistor TR3 to drop to near ground potential to result in transistor TR3 being turned off. Thus, the visual alarm V and the audible alarm A do not operate.

(2)When the switch S2 is released to open, the electrical charges stored in capacitors C2 and C3 cause TR3 and TR2 to continue to conduct so that the electrical appliance remains energised and the audible and visual alarms remain inoperative. At the same time, capacitors C2 and C3 begin to discharge through parallel resistors R2 and R3 respectively.

In both cases, a point is reached during the discharge process where there is insufficient voltage across the capacitors to maintain the transistors in conduction. However, the sizing of components C2 R2 and C3 R3 is such that transistor TR2 turns off first. As TR2 turns off, the voltage at point P WO 99/24998 PCT/AU98/00901 connected to the extra low voltage supply through R5, rises to the full available extra low supply voltage to cause FET transistor TR3 to conduct. Thus the audible alarm A and the visual alarm V operate to audibly and visually warn of an impending de-energisation of the electrical appliance.

(3)Should the appliance be required to remain in operation for a longer period than that allowed by the timing circuit consisting of C3, R3 and TR3, the momentary closure of switch S2 causes both capacitors C2 and C3 to be re-charged again to the full available DC extra low voltage supply to restart both timing circuits and to simultaneously mute the audible and visual alarms. Thus the appliance remains in use for an extended period of time as required and the process may be repeated as many times if necessary.

(4)If it is not required to extend the time for which the appliance remains energised, the alarms may be muted by the momentary closure of switch S3 to selectively re-start the timing circuit consisting of C2, R2 and TR2 by charging capacitor C2 only. Thus the alarms remain muted until TRI turns off to de-energise the relay and the electrical appliance.

The alarms are re-energised after the timing circuit associated with transistor TR2 times out again if switch S1 is still closed to alert the operator so that switch S 1 can be turned off. Thus, when switch S1 is turned off, the control and timing circuits are disabled and the appliance remains disconnected from mains supply.

The important safety feature of this invention is that, should an energised electrical appliance be left unattended, WO 99/24998 PCT/AU9800901 6 (a)TR2 turns off first to cause TR3 to turn on to operate the alarms, (b)then TRI turns off to de-energise the relay and the electrical appliance, thus eliminating any possibility of an accident such as the start of a fire, (c)the alarms remain in operation to immediately warn the operator, as soon as he or she returns to the location of the appliance, that the equipment operation has been stopped. The operator then has a choice of either re-starting the appliance or aborting the operation altogether by turning off switch S1.

Thus, it is realised that this invention provides means of safely operating an electrical appliance for any required period of time whilst also providing means to prevent the appliance from remaining in operation unchecked and unattended, a situation which could result in serious accidents.

The control circuit described in this embodiment may be incorporated as part of the electrical appliance, or built as a separate unit to which the appliance and the mains supply are connected.

Alternatively, the control circuit may be built into a portable unit designed to plug into a power outlet from which the appliance is powered. It is also to be understood that the use and purpose of this invention is not limited to the control of electrical appliances operating from mains supply only but in effect can be used for the control of all types of appliances operating from various voltage sources, AC or DC.

Claims (4)

1. An apparatus for safely operating an electrical appliance or equipment in which the appliance or equipment is powered from a source of electrical supply so as to ensure that the said appliance or equipment does not remain energised indefinitely through neglect, omission, oversight or distraction, said apparatus including:- Timing and disconnecting means for automatically switching off power to said electrical appliance or equipment after a set or selected period of time, and Audible and or visual alerting means to warn of an impending disconnection of power to the said electrical appliance or equipment through the action of the first said timing and disconnecting means as the set or selected period of time is approached or reached, and o Resetting means to re-start the said timing, disconnecting and alerting means sequence if said electrical appliance or equipment is required to operate or remain in use for a period of time exceeding the timing and disconnecting means set or selected period, and Silencing means to mute the emitted audible and or visual warning if the said electrical appliance or equipment is required to operate or remain in use for the set or selected period of time without interference by or inconvenience from the emitted warning.

2. An apparatus as claimed in claim 1, wherein the said timing and disconnecting means, the resetting means, the alerting RAmeans and the silencing means form part of the electrical appliance or equipment.

3. An apparatus as claimed in claim 1, wherein the said timing and disconnecting means, the resetting means, the alerting means and the silencing means form part of a separate unit which can be connected to a source of electrical supply and to which an electrical appliance or equipment can be connected, energised and controlled.

4. An apparatus as claimed in claim 3, wherein the said timing and disconnecting means, the resetting means, the alerting means and the silencing means form part of a separate plug- in unit which can be connected to an electrical outlet, and to which an electrical appliance or equipment can be connected to through an electrical plug. .000.: A method for safely operating an electrical appliance or equipment in which the appliance or equipment is powered from a source of electrical supply so as to ensure that the said appliance or equipment does not remain energised *o*indefinitely through neglect, omission, oversight or distraction, said method including:- Automatically switching off power to said electrical S°appliance or equipment after a set or selected period of time, and Providing an audible and or visual alert to warn of an impending disconnection of power to the said electrical appliance or equipment as the set or selected period of time is approached or reached, and Resetting the timing, disconnecting and alerting sequence if said electrical appliance or equipment is required to operate or remain in use for a period of time exceeding the set or selected period, and Silencing or muting the emitted audible and or visual warning if the said electrical appliance or equipment is -9q- required to operate or remain in use for the set or selected period of time without interference by or inconvenience from the emitted warning. .Co 06 01:6