GB2163308A

GB2163308A - Switching apparatus

Info

Publication number: GB2163308A
Application number: GB08517098A
Authority: GB
Inventors: Brian George Feasey
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1984-07-07
Filing date: 1985-07-05
Publication date: 1986-02-19
Also published as: GB8517098D0; GB8417415D0

Abstract

Two operator switches 4 and 6 are serially coupled with a sampling switch 8, a switch state detector 12 and two timers 18 and 20 between a grounded terminal and a power switch 22 of electrical equipment. When either of the switches 4 and 6 are operated, the path to earth is detected by the detector 12 and a signal is passed to the appropriate timer 18 or 20. The timers 18 and 20 do not however provide a signal to operate the power switch 22 unless either switch 4 or 6 is operated for longer than the time periods of the timers 18 and 20 (eg. two seconds). <IMAGE>

Description

SPECIFICATION Switching apparatus The present invention relates to switching apparatus and in particular, but not exclusively, to switching apparatus incorporated in electrical equipment.

Electrical equipment, such as a transceiver, is normally provided with an externally mounted switch to enable the equipment to be switched off when not in use. These switches can take many forms but push-button or toggle switches are frequently used for this purpose.

Switches of this type, however, require only a simple physical action to operate and hence, are subject to accidental actuation. External switches on portable communications equipment are particularly susceptable to accidental actuation during transit of'the equipment.

Such equipment is usually battery powered and, therefore, accidental switch operation during transit can lead to discharge of the supply batteries and failure of the equipment.

It has previously been proposed to remedy this problem by using multistep mechanical rotary switches or switches which require multiple key strokes for operation. However these types of switches produce an increase in the complexity of the design or operation of the equipment.

It is an object of the present invention to provide switching apparatus which is simple to actuate but which is less susceptible to accidental operation than the above mentioned types of switches.

Switching apparatus comprising a serially coupled operator switch, an earth leakage detector and a timer, for connection with a grounded terminal and a power switch of electrical apparatus, arranged such that the operator switch must be activated for longer than a predetermined period of time, as determined by the timer, before the power switch of the electrical apparatus, to which the switching apparatus is arranged for connection, is activated.

The present invention will now be described, by way of example, with reference to the accompanying drawings which illustrates a schematic diagram of switching apparatus in accordance with the present invention.

Referring to the drawing, switching apparatus 2 comprises operator switches 4 and 6 such as conventional mechanically actuated push-button switches. The switch 4 may be used to switch on equipment in which the switching apparatus is incorporated and the switch 6 may be used to switch off the equipment.

One terminal of the switches 4 and 6 is connected to ground, such as a grounded terminal of the equipment, and the other terminal of each switch 4 and 6 is connected to terminals on a change over sampling switch 8. The common terminal on the sampling switch 8 is connected to input 10 of an earth detector 12.

The earth detector 1 2 is provided with outputs 14 and 1 6 to indicate respectively when the switches 4 and 6 have been made.

The outputs 14 and 6 of the earth detector 1 2 are connected via timers 1 8 and 20 to a main power switch 22. The timers 1 8 and 20 have, preferably, a predetermined time period of two seconds and the power switch 22 is connected in the main power supply line of the electrical equipment incorporating the switching apparatus.

The switching apparatus 2 operates as follows. The sampling switch 8 samples sequentially, the state or condition of the switches 4 and 6, that is, whether the switches 4 and 6 are in a make or break condition.

When either of the switches 4 and 6 are made this will be recognised by the earth detector 1 2 as the input 10 of the earth detector 1 2 is connected to ground through the sampling switch 8 and the made switch 4 or 6.

The earth dertector 1 2 then provides an output signal on either output 1 4 or 1 6 which is fed through either timer 1 8 or 20 to the power switch 22. The power switch 22 is actuated to switch on or switch off the equipment. However, as the timers 1 8 and 20 are located in the lines between the earth detector 1 2 and the power switch 22 the input 10 of the earth detector 1 2 must be connected to ground for at least the predetermined time period of the timers 1 8 and 20 to enable the output signal from the earth detector 1 2 to pass through either timer 1 8 or 20 to the power switch 22.As the input 10 is connected to ground through either switch 4 or 6, switch 4 or 6 must be activated for at least the predetermined time period of timers 1 8 and 20 before the power switch 22 is operated. For example, assume that it is required to switch on the equipment and that the timers 1 8 and 20 have predetermined time periods of 2 seconds. The switch 4 is made to connect the input 10 of the earth detector 1 2 to ground through the switch 4 and the sampling switch 8. The earth detector 12 produces an output signal on output 14 which is fed to timer 1 8. However, a signal does not appear on the output of timer 1 8 for 2 seconds and hence, the switch 4 must be made for at least two seconds before the power swith 22 is actuated. If the switch 4 is made for less than 2 seconds the signal is removed from the input of the timer 1 8 before the expiry of the 2 second time period and hence, the power switch 22 is not actuated. It can be seen, therefore, that a request to switch on or switch of the equipment must persist for at least the predetermined time period set in timers 1 8 and 20 before the power switch 22 is activated.

Claims

1. Switching apparatus comprising a serially coupled operator switch, an earth leakage detector and a timer, for connection to a grounded terminal and a power switch of electrical apparatus, arranged such that the operator switch must be activated for longer than a predetermined period of time, as determined by the timer, before the power switch of the electrical apparatus, to which the switching apparatus is arranged for connection, is activated.

2. Switching appartus according to claim 1 comprising two operator switches and two timers serially coupled with the earth leakage detector and wherein the switching apparatus is arranged for one operator switch to be operative to make the power switch of the electrical apparatus and the other operator switch to be operative to break the power switch of the electrical apparatus when the appropriate operator switch is activated for longer than the predetermind period of time.

3. Switching apparatus according to claim 2 comprising a scanning switch, serially coupled to the operator switches, for monitoring the condition of the two operator switches.

4. Switching apparatus according to any one of claims 1 to 3 wherein the operator switches comprise push button switches.

5. Switching apparatus substantially as hereinbefore described with reference to the accompanying drawing.