Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-10-05
2002-01-08
Wu, Daniel J. (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S568300, C340S540000, C340S686300, C340S691300, C340S693110
Reexamination Certificate
active
06337633
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an alarm cable capable of being installed between electrical appliances and one or more power or data signal sources, thereby securing the appliance against theft in addition to functioning as a power or data signal supply cable.
With an alarm cable according to the invention, it is ensured that an alarm signal is triggered when an attempt is made to disconnect the alarm cable from the power or data signal source or the equipment that is to be secured. This will complicate the execution of a theft.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,418,521 teaches an alarm cable which, apart from the regular conductors for mains current (and earth), also comprises two conductors which form part of a current loop around the alarm cable plug to the mains socket outlet, wherein positioned within the plug is a switch for closing or opening the current loop upon disconnection from or connection to the mains socket outlet. The switch is embedded in the plug, but can nevertheless be actuated via an arm on connection to or disconnection from the mains supply.
U.S. Pat. No. 5,418,521 has no facility for discriminating between an alarm signal in the event of an actual attempted theft and an alarm signal in the event of an ordinary loss of supply voltage, inasmuch as it detects changes of state of the switching loop in the same loop as it detects supply voltage presence.
Furthermore, the alarm cable in the U.S. patent is not capable of triggering an alarm when the alarm cable is disconnected from the equipment that is to be secured if an unauthorised person first peels off the insulation around the cable, and connects an external loop in the switching loop between the alarm electronics box and the connector at the end of the cable.
Another weakness of the U.S. patent is that the “alarm box” is located at a point along the cable between the connectors at the two ends of the cable, which means that the acoustic alarm signalling unit is easily accessible to unauthorised persons who can deaden the alarm sound in a number of ways, e.g., by lowering the whole “alarm box” into a container full of water.
A further weakness with the U.S. patent is that the alarm circuit is not connected to any locking function for the cable to the equipment that is to be secured. This means that an unauthorised person can disconnect the alarm cable from the equipment that is to be secured, and leave the alarm behind whilst disappearing with the equipment that is to be secured.
SUMMARY OF THE INVENTION
Referring to
FIGS. 1
a
,
1
b
,
2
,
3
,
4
and
5
, it is therefore an object of the invention to provide an alarm cable which includes at least two connector devices selected from a number of different types of connector, wherein each connector device includes an electric switch, which switch forms an electric switching loop which is closed when the connector device is brought together with a female connector and is opened when the connector device is moved from a female connector, at least one alarm signalling device, and at least one electrically conducting wire of the multi-conductor type to form electrical connections between the connector devices of the alarm cable, wherein at least one connector device is connected to the conductors in a wire, whereof two conductors at the first end area of the wire are connected electrically to their respective sides of the switching loop to form a current loop, characterised in that at least one connector device also includes a loop detector having a plurality of inputs connected respectively to the respective switching loop of the connector and to two current loop conductors of the connecting wires at the other end area of the wires, which loop detector supplies a signal when there is a change in one or more of the electrical properties of the current loop or when there is a change of state in the aforementioned respective switching loop, a voltage detector, which voltage detector detects the presence of an electric voltage supplied from an external electric power source through one or more connector devices and which gives a signal upon loss of voltage, a control circuit connected to the loop detector and the voltage detector, which control circuit sends a control signal of limited duration in response to the presence of a signal from the voltage detector only, which control circuit sends a prolonged control signal in response to the presence of signals from the loop detector only or on the concurrent presence of signals from both the loop detector and the voltage detector, and an alarm signalling device which receives the aforementioned control signals and which gives at least one alarm signal in response to the presence of control signals.
Protection of equipment is achieved according to the invention in that an alarm cable is plugged into the power or data signal input terminal in the equipment that is to be secured, and to a power or data signal source, such as the mains supply. Voltage from the power or data signal source is detected by a voltage detector. Furthermore, there runs from a control circuit a current loop via switches in the alarm cable connectors, which is opened or closed upon disconnection from or connection to the equipment that is to be secured and also the power or data signal source. A similar current loop at the loop detector of resistor elements in the cable connectors detects any changes of state in the electrical properties of the loop, and gives an alarm on “unauthorised connection” of the loop along the cable between the connectors. In another current loop a fixing pin(screw) and (a washer at) the fastening piece are connected in series, so that via the control circuit a prolonged alarm signal is given when changes in the electrical properties of the loop occur upon unauthorised manoeuvring of the fixing pin.
REFERENCES:
patent: 3598930 (1971-08-01), Desnoes
patent: 3774189 (1973-11-01), Brown
patent: 5418521 (1995-05-01), Read
patent: 5440441 (1995-08-01), Ahuja
patent: 5714942 (1998-02-01), Buchanan
patent: 0 470 058 (1992-02-01), None
patent: 2 158 277 (1985-11-01), None
Nguyen Tai T.
Safety Cable AS
Wu Daniel J.
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