GB2080568A - Programmed time switch - Google Patents

Abstract

A time switch unit for operating an electrical appliance, e.g. a photocopying machine. The unit includes a first time switch programmed with a continuous duty cycle of switch-on and switch-off periods which can be determined such that the appliance is automatically switched off when unattended e.g. at night. A second time switch provides for temporary manually operated switch-on during the switch-off period of the first time switch.

Description

SPECIFICATION Programmed time switch This invention relates to programmed switching apparatus and in particular to apparatus for disabling and enabling electrical equipment according to a predetermined programme.

The modern office has the need to use electrical appliances to a greater degree than ever before.

Insurance premiums are related to fire risk and a reduction in premiums can often be obtained if the insurers can be convinced that all electrical appliances are rendered safe, i.e. disconnected, outside normal working hours. As a result of the trend towards flexible working hours, overtime and the need in many organisations to have security staff and cleaners in the office outside normal working hours it is very difficult to control the disconnection of appliances.

One particularly sensitive area concerns office copiers some of which run at an elevated temperature and, if left switched on overnight, or at weekends can be a serious fire hazard. Also office copiers which have been left on can be subject to use by unauthorised persons.

According to the invention there is provided a programmable time switch unit for connecting selectively an electrical appliance to a power supply, including a first time switch device programmed or programmable with a continuous duty cycle of switch on and switch off periods, a second time switch device having a relatively shorter switch on duty period commencing from the application of electrical power thereto, and switch means for interpositioning between the power supply and the appliance, said switch means being closed by the first or second time switch devices when in the switch-on portion of a respective duty cycle, the unit being such that, when the first time switch device is in the switch-off portion of its duty cycle, application of power to the second time switch device causes the switch means to close for the duty period of the second device so as to connect the power supply to the appliance during that period.

In use the controlled equipment may for example be on during the working day, automatically switched off at the close of the day but able to be used outside normal working hours after operating a push button which would over-ride the off switch for a period of say 10 minutes. In some applications the push button may be replaced by a key operated switch the use of which can then be restricted to authorised persons.

An embodiment of the invention will now be described with reference to the accompanying drawing in which the single figure represents a schematic circuit diagram of the programmable time switch unit.

Referring to the drawing, the time switch unit, which, when in use, is coupled to the electrical mains, includes first and second timer units 11 and 12 respectively the first of which, 11, operates a double pole contactor 13. The contactor 13 is connected to the line and neutral leads, Land N, and, when in its open position, isolates the unit output, OPL and OPN, from the mains input. Operation of the contactor is provided via a solenoid 14 which is energised via the contacts RLB1 of a relay RLB which in turn is operated by the timer 11.

The relay contacts RLB1 are connected in parallel with contacts RLA1 of a second relay RLA which relay is operable via the second timer 12 upon closure of a switch S1, this switch being of the type that is biased to its open position. Mains power to the second timer unit is supplied by closure of the switch S1 and is maintained after release of the switch S1 via contacts RLA2 of the relay RLA. The second timer is preset to maintain the power to the relay RLAfor a predetermined period, e.g. 10 minutes, after which the relay is de-energised releasing contacts RLA1 and RLA2.

The operation of the programmable switching unit is as follows.

The timer 11 is programmed according to a predetermined operating cycle. Typically this will be a seven day cycle providing switch-on of an electrical appliance (not shown) to which the unit is coupled, e.g. from 9 a.m. to 5 p.m. from Monday to Friday. This programming may be effected by a conventional mechanical or electro-mechanical arrangement or, advantageously, by a microprocessor control device which can be programmed to operate automatically for several years taking into account fixed date public holidays and, annual shut-down periods.

During the 'on' period of the duty cycle of the timer 11 the relay RLB is energized thus closing contacts RLB1 and maintaining the power supply to the contactor 13 which in turn connects the controlled electrical appliance to the line and neutral supplies from the mains. At the end of the 'on' period the power to the relay RLB is disconnected and the contacts RLB1 open thus releasing the contactor 13.

Whilst the timer 11 is in the 'off' portion of its duty cycle mains power may be restored temporarily to the controlled appliance by engagement of switch S1 which supplies power to the second timer 12 and sets that timer to the start of its timing cycle. Setting of the timer 12 by the switch S1 causes power to be supplied to the relay RLA thus closing contacts RLA, which supply power to the appliance, and contacts RLA2 which maintain the power supply to the timer after the switch S1 has been released. The timer 12 has a relatively short timing cycle, typically 5 to 15 minutes, at the end of which the power supply to the relay RLA is disconnected thus releasing contacts RLA1 and RLA2, the latter disconnecting the power supply to the timer.If desired the switch S1 can again be operated to provide a further period during which power is supplied to the appliance.

The arrangement described above may be used to prevent an electrical appliance from being left on accidentally during periods when it is unattended whilst providing for an emergency switch-on facility during the switch-off period. In certain applications, e.g. where the unit is connected to or incorporated in a photocopying machine, the push-button switch S1 may be replaced by a key operated switch. This ensures that, during the switch-off period, the ap pliance can be operated only by authorised key holders.

in a further application the arrangement may be incorporated in a central heating programmer unit to provide a preset cycle of switch-on and switch-off periods whilst providing for an 'overide' switch-on for a predetermined period, e.g. 1 hour. The arrangement thus prevents the heating system from being left on inadvertantly for long periods when overide has been initiated.

Claims (7)

1. A programmable time switch unitforconnecting selectively an electrical appliance to a power supply, including a first time switch device programmed or programmable with a continuous duty cycle of switch on and switch off periods, a second time switch device having a relatively shorter switch on duty period commencing from the application of electrical power thereto, and switch means for interpositioning between the power supply and the appliance, said switch means being closed by the first or second time switch devices when in the switch-on portion of a respective duty cycle, the unit being such that, when the first time switch device is in the switch-off portion of its duty cycle, application of power to the second time switch device causes the switch means to close for the duty period of the second device so as to connect the power supply to the appliance during that period.

2. Aprogrammable time switch unitforcoupling selectively an electrical appliance to a power supply, including a first time switch device programmed with a continuous duty cycle of switch-on and switch-off periods, a solenoid operable contactor interposed between the power supply and the appliance, a first relay operable by the timer device and having a set of contacts in series with the contactor solenoid whereby power can be applied selectively to the solenoid, a second time switch device having a relatively short switch-on duty period commencing from the application of electrical power thereto, switch means for applying power selectively to the second time switch device, and a second relay operable by the second timer device and having a first set of contacts in parallel with the contacts of the first relay, and a second set of contacts in series with the power supply to the second time switch device, the arrangement being such that, when the first time switch device is in the switch-off portion of its duty cycle whereby the power supply to the contactor is disconnected, selective closure of the switch means causes said second time switch device to energize the second relay for the duty period of the device so as to restore power to the contactor and thereby to the appliance for the duration of that duty period.

3. Atime switch unit as claimed in claim 2, wherein said switch means comprises a key operated switch.

4. A time switch unit as claimed in claim 1,2 or 3, wherein said first time switch device is controlled by a programmed microprocessor.

5. A time switch unit substantially as described herein with reference to the accompanying drawings.

6. An electrical appliance incorporating or coupled to a time switch unit as claimed in any one of claims 1 to 5.

7. A central heating programmer unit incorporating a time switch as claimed in any one of claims i to -: 5.