GB2101377A - Signal interface - Google Patents

Abstract

An interface is provided for the connection of burglar alarm, fire alarm and the like devices with a telecommunications network. The interface serves by the use of isolating relays or fast-acting fuses to block the passage of unacceptably high voltages and currents to the network. The interface is a separate item which may be certified as effective by the appropriate telecommunications authorities. Devices which are connected through the interface then no longer require to meet the standards of isolation normally applied to items to be connected to a telecommunications network. The interface will be provided in its own housing which, in the case of a burglar alarm, will suitably also include anti- tamper devices. Tampering is sensed by a microswitch 16 or by normally separated contacts 18, 20. <IMAGE>

Description

SPECIFICATION Signal interface This invention relates to the transmission of electrical signals and more particularly to the connection of signal generation devices with signal networks, principally the G.P.O. network.

There are numerous applications in which advantage can be obtained by connecting signal generation devices directly with the G.P.O.

network. A particular example is the fire or burglar alarm device in an unattended building, the device being connected through the G.P.O. network with a remote monitoring station. Great care has of course to be taken that such devices do not introduce unacceptably high voltages or currents into the network and G.P.O. approval is generally required of each separate type of device which it is desired to use. This is inconvenient for manufacturers, users and the G.P.O.

It is an object of this invention to provide an improved system by which this disadvantage is overcome.

Accordingly, the present invention consists in a system for the transmission of electrical signals to a signal network, comprising a connection to the network; a signal generation device and an interface separate from said signal generation device and connected between the device and said network, the interface serving to transmit signals and to block the passage of unacceptably high voltages or currents.

Advantageously, the interface includes a relay operable by signals from said generation device.

Preferably, the interface includes anti-tamper devices connected in a fuse-protected anti-tamper line.

In a further form, the invention comprises an interface suitable for use in such a system.

The invention will now be described by way of example with reference to the accompanying drawing which shows in diagrammatic form an interface according to the present invention.

In the drawing there is shown a plastics housing 10 which is provided with screw mounting holes 12. The housing further includes a cover which is not shown in the drawing but which is held in place by means of screws which pass through the cover and engage in corresponding nuts anchoring beneath apertures 14 in the drawing.

At the left hand side, as seen in the drawing, the housing is provided with a micro-switch 16, the lever of which engages the surface upon which the interface is mounted. The micro-switch is accordingly held in the closed position unless an attempt is made to remove the interface. The housing is provided with a second anti-tamper device in the form of contact leaves 18 and 20 which are normally held in electrical contact by the pressure of the cover. Any attempt to remove the cover will result in loss of electrical contact between the leaves 1 8 and 20. The leaf 1 8 is provided with a tag for connection to the incoming anti-tamper line. The leaf 20 is connected to one terminal of the micro-switch 16, the other terminal of which is connected to junction element 22.

Inside the housing 10, there is provided a printed circuit board upon which are mounted the circuit elements shown in the drawing. For clarity, the circuit elements are shown in circuit diagram form. It will be seen that the terminals of junction element 22 are connected through respective fast blow fuses 24 with the terminals of junction element 26. Between each fuse and the junction element 26, there is connected the anode of a "back-to-back" pair of Zener diodes 28, the other anode in each case being connected to an earth line 30 extending to an earth tag 32.

The terminals of a third junction element 34 are connected to opposite ends of the coil 36 of a read relay 38. A diode 40 is connected in parallel with the coil. The contacts of the relay 38 are connected with the terminals of a fourth junction element 42.

In use, the positive and negative outputs of a signal generating device are connected respectively with the terminals of junction element 34. The earth line is connected to earth tag 32 and the anti-tamper lines are connected one to the free terminal junction element 22 and the other to the tag of contact leaf 1 8. The terminals of junction element 42 are connected with the signal network and the terminals of contact element 26 are connected with the outgoing anti-tamper lines.

It will be appreciated that the signal network is isolated from the signal generating device by the relay 38. Further; the passage of any unacceptably high voltages or currents along the anti-tamper lines is prevented by the fuses 24 and the Zener diodes 28.

The described interface is particularly useful in connection with the recently introduced alarm by carrier system in which burglar and fire alarm devices are connected through ordinary telephone lines to a central processor. The condition of each alarm device, and the associated anti-tamper lines if these are fitted, is monitored by the central processor which transmits an appropriate signal to an information unit in the event of an alarm call.

With the interface according to the present invention, a great variety of fire, burglar and other alarm devices can be used in the alarm by carrier system - or indeed in any other telephone system -- without the need for each device to be separately approved.

It should be understood that the interface can be used in a great variety of applications where it is necessary to connect a signal generation device with a telephone line or any other signal network.

In this applications, the anti-tamper devices may or may not be necessary.

The invention has been described by way of example only and numerous modifications are possible without departing from the scope of the invention. Other circuit elements could, for example, be employed to ensure that the interface transmits signals yet blocks unacceptably high voltages and currents. The interface could, moreover, be provided in a housing of other forms.

Claims (5)

1. A system for the transmission of electrical signals to a signal network, comprising a connection to the network; a signal generation device and an interface separate from said signal generation device and connected between the device and said network, the interface serving to transmit signals and to block the passage of unacceptably high voltages or currents.

2. An interface according to Claim 1, wherein the interface includes a relay operable by signals from said generation device.

3. A system according to Claim 1 or Claim 2, wherein the interface includes anti-tamper devices connected in a fuse-protected anti-tamper line.

4. An interface suitable for use in the system according to any one of the preceding claims.

5. A system for the transmission of electrical signals to a signal network, including an interface substantially as hereinbefore described with reference to and as shown in the accompanying drawing.