GB2217933A - Time lag switching device - Google Patents

Abstract

In a two-terminal timer, particularly for lights 1, momentary closure of a switch 3 resets an intergrated circuit timer 10 and discharges a capacitor C1 in the direction A to B through the coil 4 of a latching relay thereby closing relay contacts 5 to energise the lights 1. When the timer 10 times out, a transistor 11 is turned on to discharge a capacitor C2 in the direction B to A through the coil 4 thereby opening contacts 5 to turn the light 1 off. The timing period can be extended by momentary closure of switch 3 before the timer 10 times out, but not by maintaining switch 3 closed. In an alternative enbodiment, (Fig 3), the latching relay is of the type having two coils (12). <IMAGE>

Description

TIME LAG SWITCHING DEVICE This invention relates to a time lag switching device of the type used for temporary illumination of, for example, staircases and landings in blocks of flats or other buildings. Such devices may equally well be used for timing processes, particularly industrial processes.

Time lag switches are widely used for temporary illumination of staircases and landings in buildings where these are not illuminated by daylight and can therefore be dangerous. On entering the building a person simply pushes a button and the light comes on for a preset period, usually about 5 minutes; and it is then switched off automatically by the time lag switch. This makes the stairs safe when being used, and saves electricity when they are not in use.

There are at present three main types of time lag switches available. The first is a pneumatically-controlled switch, which requires considerable pressure to be applied to the push-button switch to operate it and the timing of this known switch can be difficult to adjust and inaccurate. However, this device does not generally require a separate neutral and can therefore replace an ordinary light switch.

The second time lag switch available is the solidstate electronic type, which also does not require a separate neutral and can thus directly replace an ordinary light switch. This switch does however, have the serious disadvantage of not being able to switch fluorescent lights.

The third known type of time lag switch includes an electronically timed relay, and is able to switch both incandescent and fluorescent lamps, but requires a separate neutral connection. This is a major disadvantage because it makes wiring into the circuit more difficult, especially in existing installations already wired for pneumatic or solid state timers.

It is an object of the present invention to provide a time lag switching device which can switch both fluorescent and incandescent lamps1 and is capable of operating without a separate neutral and can therefore be wired in place of an ordinary light switch.

It is another object of the present invention to provide a time lag switching device, the timing period of which can be adjusted relatively easily and accurately.

Accordingly, the present invention consists in a time lag switching device comprising latching relay means to control switching on and off of power to a load, a timing circuit for timing a predetermined time period, and switching means operable to cause said latching relay means to assume a state, in which the power is switched on, and said timing circuit to commence timing of said time period, said timing circuit being arranged 0 cause said latching relay means to change to another case, in which the power is switched off , at the end of said time period.

In a preferred embodiment, said timing circuit includes an electronic timer for timing said time period and means, activated by operation of said itching means, to re-set said timer, such that, upon subsequent operation of said switching means during said time period, said timer recommences timing of said time period. The timing circuit preferably also includes a variable resistor-capacitor timing control connected to said timer to enable the duration of said time perioa to be adjusted.

The latching relay means preferably includes a latching relay and capacitor means for causing current to flow through said latching relay in a direction to switch said latching relay into said switched-on state, and a transistor arranged to be activated by said timer to cause current to flow through said relay in an opposite direction to return said latching relay to said switched-off state at the end of said time period.

The switching means may comprise a plurality of switches connected in parallel, such that operation of any one of said switches activates the device.

Advantageously, the latching relay is of the single coil, electromagnetic type. In another embodiment, the latching relay may be of the two-coil or split-coil, electromagnetic type.

The device, in accordance with the present invention, is intended to be connected between a live line of a mains power supply and the live side of the load, the other side of which is connected to the neutral line. The load may comprise one or more incandescent lamps, to which the device can be connected and through which it is supplied directly. In another example, the load may comprise one or more fluorescent lamps, to which the device can be connected and in which case it is supplied through one or more power factor correction capacitors.

In order that the present invention may be more readily understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 shows a block circuit diagram of a time lag switching device, in accordance with an embodiment of the present invention, Figure 2 shows a more detailed circuit diagram of the embodiment in Figure 1, and Figure 3 shows a circuit diagram of another embodiment of the invention.

Referring to Figure 1, there is shown a time lag switching device having two terminals T1,T2 connected respectively to a live line L of a mains power supply and to a neutral line N via a load 1, which preferably consists of one or more incandescent or fluorescent lamps. Voltage applied to the device is rectified by bridge rectifier 2 and the rectified voltage then charges capacitors C1 and C2. When switch 3 is closed, a current flows through a latching relay 4, (otherwise known as a remanence or bistable relay), preferably of the 16A silver-cadmium oxide type, from capacitor C1 to capacitor C2, and thereby causes the relay to assume a switched-on state. This closes relay contact 5 and switches power to the load 1.Closure of the switch 3 also causes integrated circuit timer 10 to commence timing of a predetermined time period and also activates a re-set circuit 7.

At the end of the time period, the timer 10 activates a transistor 11, which causes current to flow in the opposite direction through the relay 4, so that the relay changes to a switched-off state, which opens relay contact 5 and switches off the power to the load 1. Subsequent closure of the switch 3, either during or after the time period, causes the timer 10 to be re-set by the re-set circuit 7, so that timing of the time period is recommenced. A main storage capacitor is provided at C7.

Operation of the device, in accordance with the invention will now be described in more detail with reference to Figure 2.

Voltage is applied to the timer 10, which is preferably of the 4541 CMOS type, via the live supply L direct, and via the neutral N through the lamps constituting the load 1, directly in the case of a filament lamp or through power factor correction capacitors C8,C9 in the case of fluorescent lamps. The voltage is then rectified by the bridge rectifier 2 formed by diodes D1,D2,D3,D4. The rectified voltage then charges capacitor C1 to about 30V, capacitor C2 to about 12V and capacitor C7 to about llV in the space of approximately 5 seconds after the power is first switched on and before the light is switched on. When the switch 3, which consists of a master push-switch and slave push-switches connected together in parallel, is closed, a current will flow from capacitor Cl to capacitor C2 (ie. from higher to lower voltage) through the single coil of the latching relay 4 in the direction A to B,which causes the relay 4 to change state (switch on). Also, on closing the push-switch a positive pulse is applied to reset pin 6 of the integrated circuit timer, via capacitor C6. This resets the timing of the timer 10 so that the state of its output on pin 8 is low.

The timer then starts timing out, the timing period being determined by resistors R4,R5,R6 and capacitor-resistor C5,R5 constituting a variable timing control. At the end of the set time, the state of the output on pin 8 of the timer 10 changes to high and this momentarily activates transistor 11 as capacitor C4 charges. While transistor 11 is activated, a current will flow from capacitor C2 to the negative line through the relay coil and the transistor but this time in the direction B to A. This, being in the opposite direction from the original magnetising current which switched the relay 4 on, will cause the relay 4 to change state (switch off).

As soon as the relay contacts 5 open ar5 switch the lamps off, capacitors C1,C2 and C7 are immediately recharged.

If during the timing period when the lamps 1 are on, either the master switch or any of the slave-switches of switch 3 are closed, then again a small positive pulse applied from capacitor C1 via capacitor C6 will reset the timer 10 to zero and the full timing period will recommence.

Thus, the time lag switching device is resettable as normally required of such a device.

Whilst the relay contact 5 is closed and the lamps 1 are switched on, no voltage is applied to the timer 10, thus leaving it powered only by the energy stored in capacitor C7 which, in the case of a 2200 pF capacitor, is sufficient to keep the device going for at least three hours. The energy required to open the relay 4 is stored in capacitor C2 which is chosen as 220 pF and also holds enough charge for at least three hours, whilst the normal period for staircase lighting is generally between 3 and 10 minutes.

The function of diodes D5,D6 and D7 is to prevent capacitors C2 and C7 discharging into other parts of the circuit, diode D7 is particularly important in this respect since it prevents capacitor C7 from discharging when the transistor 11 is activated. The function of diode D8 is to discharge capacitor C6 slowly ready for the next reset pulse and with the minimum loss of energy.

Zener diodes D9 and D1O clamp the voltage to 30V and 12V respectively.

A transient suppressor, consisting of a suppressor 7 and a limiting resistor R8, prevents damage to the bridge rectifier 2 which may be caused by very Kligh back EMF produced by some economy fluorescent lamps. A IN4007 diode Dll is provided to prevent capacitor C1 from discharging through resistors R1 and R2 and diode D5 into capacitor C2.

Figure 3 shows another embodiment of the device, in accordance with the invention. In the circuit shown in Figure 3, like parts have been labelled with like references, with respect to Figures 1 and 2. This circuit also operates in the same manner as the circuit in Figure 2, but utilises a two-coil or split-coil latching relay 12, instead of the single coil latching relay 4.

An important and unique feature of the time lag switching device in accordance with the invention, is that, unlike any of the known available types, it is not possible for anyone to keep the lights switched on by retaining the switch button in a depressed position, e.g. by means of a matchstick, etc. If this is attempted, the device will simply time out and switch off until the obstruction to the push-switch is removed and the timer is restarted.

In a particular embodiment of the present invention, the circuit components of the device are of the following types : - D1,D2,D3,D4 - WO8 Bridge Rectifier D5,D6,D7 - 154007 Rectifier D9 - BZY88 C30 30 volt Zener Diode or equivalent D10 - BZY88 C12 12 volt Zener Diode or equivalent D8 - 1N4148 Diode 10 - 4541 Integrated Circuit Timer 11 - BC337 Transistor C1 - l00uF 35V Electrolytic Capacitor C2 - 220pF 16V Electrolytic Capacitor C3 - 0.1 F 250V Polyester Capacitor Cl - 4.,pF 25V Electrolytic Capacitor C5 - 0.0082nnF Polyester Capacitor C6 - 0.0033 F 50V Ceramic Capacitor C7 - 2200,uF 16V (or 1000 F) Electrolytic Capacitor C8 - 0.00luF 50V Ceramic Capacitor 1 - 150K 1/2W Resistor R2 - 56K 2W Resistor R3 - 47K 1/4W Resistor R4 - 100K 1/4W Resistor P.5 - 10M Adjustable Potentiometer R6 - 1M 1/4W Resistor R7 - 100K 1/4W Resistor 3 - Push-to-Make Switch 4 s 5 - Bistable Relay Coil & Relay Contacts (16 Amp).

The power factor correction capacitors C8,C9 do not form an ntegral part of the device and their values can vary depending on the power factor of the balast in a particular fitting.

Whilst particular embodiments of the present invention have been described, various modifications will be envisaged without departure from the scope of the invention.

Claims (10)

1. A time lag switching device comprising latching relay means to control switching on and off of power to a load, a timing circuit for timing a predetermined time period, and switching means operable to cause said latching relay means to assume a state in which the power is switched on and said timing circuit to commence timing of said time period, said timing circuit being arranged to cause said latching relay means to change to another state in which the power is switched off at the end of said time period.

2. A device as claimed in Claim 1, wherein said timing circuit includes an electronic timer for timing said time period and means, activated by operation of said switching means, to re-set said timer, such that, upon subsequent operation of said switching means during said time period, said timer recommences timing of said time period.

3. A device as claimed in Claim 1 or 2, wherein the timing circuit includes a variable resistor-capacitor timing control connected to said timer to enable the duration of said time period to be adjusted.

4. A device as claimed in claim 1,2 or 3, wherein the latching relay means includes a latching relay and capacitor means for causing current to flow through said latching relay in a direction to switch said latching relay into said switched-on state, and a transistor arranged to be activated by said timer to cause current to flow through said relay in an opposite direction to return said latching relay to said switched-off state at the end of said time period.

5. A device as claimed in any preceding claim, wherein the switching means comprises a plurality of switches connected in parallel1 such that operation of any one of said switches activates the device.

6. A device as claimed in any preceding claim, wherein the latching relay is off the single coil, electromagnetic type.

7. A device as claimed in any one of claims 1 to 5, wherein the latching relay is of the two-coil or splitcoil, electromagnetic type.

8. A device as claimed in any preceding claim, wherein the load comprises one or more incandescent lamps, to which the device can be connected and through which it is supplied directly.

9. A device as claimed in any one of claims 1 to 8, wherein the load comprises one or more fluorescent lamps, to which the device can be connected and in which case it is supplied through one or more power factor correction capacitors.

10. A time lag switching device substantially as herein described with reference to Figures 1 and 2 or Figures 1 and 3 of the accompanying drawings.