Pressure Mats

Pressure mats are used for detecting the movement of an intruder over a carpeted floor or stairs. They are not used that extensively in recent systems due to their unreliability and short life span. We shall however have a look at how they operate.

Mats are concealed under carpet where the intruder is likely to step, such as beside a window or on a step of stairs. Unlike any other detection device a pressure mat is open circuit, that is, the detection loop is open circuit until the mat is stepped on, when the circuit closes it is for this reason that the connections to the panel are somewhat different to other devices.

A pressure mat is constructed from two sheets of electrically conductive foil, insulated by a thin layer of sponge. This sponge has small holes cut in it about 10mm in diameter. When pressure is applied to the mat the arrangement is compressed and the two sheets of foil will touch through the holes in the sponge, thus closing the circuit (a diagram of this can be seen overleaf). The foil, sponge and electrical connections are covered by a thin plastic cover which is sealed to prevent dust impairing its operation.

OPERATION AND WIRING OF PRESSURE MATS
Below we see a diagram of the workings of a pressure mat. Because this is an open circuit device it is wired between the detection loop and the tamper loop. When pressure is applied to the mat and the circuit closes, this will short these two loops together and thus activate the alarm system.

NOTES ON INSTALLATION

Mats should be sited under the carpet in a position where an intruder is likely to walk. The mat is tacked down by using the tags provided. Be sure not to put nails or staples through the working surface of the mat or it will be rendered useless.