Communications: electrical – Condition responsive indicating system – With particular coupling link
Patent
1980-05-15
1982-08-31
Rubinson, Thomas A.
Communications: electrical
Condition responsive indicating system
With particular coupling link
340531, 340506, 340536, 340573, 34082536, 455 9, 455 11, G08B 108, H04Q 700
Patent
active
043475019
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an installation for transmitting alarm signals, primarily in cases of personal attack, and localizing alarm transmitters.
DESCRIPTION OF PRIOR ART
For the staff of hospitals, prisons and other custodial institutions there is a need for calling for help in assault or battery by means of an alarm sender which can be carried in a pocket.
In such installations it is important that the place from which an alarm has been sent can be localized. Localization can be done with aid of an alarm receiver, so that every room in a building is provided with an alarm receiver. In such case since only the alarm receiver in the room where the alarm signal has been sent reacts to an alarm, localization is carried out simply. Thus the propagation of the alarm signal is limited by the walls of the room when the alarm signal is sent supersonically or by infrared light. A serious drawback with alarm transmission in this mode is that transmission is hindered or heavily dampened if the alarm sender is kept under clothes or if it were to be under the body during a struggle. It should specifically not be necessary to take out the alarm sender in an assault, since this itself can initiate the aggressive action.
If a radio transmitter is used instead for sending the alarm, it can be carried in the clothes and does not need to be taken out to send an alarm, since radio transmission penetrates through clothes quite easily. The good penetration ability of radio transmission, however, excludes localization of the alarm sender with the help of receivers in each room, since the emissions from the transmitters are not limited by the walls of a room. Attempts to localize such an emission by taking bearings is made impossible by all the reflections obtained from the building walls.
It would be easy to localize the radio transmitter sending an alarm if the transmission contained a code notifying the location of the alarm sender, but requiring staff to set a variable room code on their alarm senders is not reasonable in practice. Staff should not need to think about the alarm sender except at the moment when it needs to be used.
SUMMARY OF THE INVENTION
According to the present invention, a room code is automatically set in the alarm sender, giving its position in the building. The set room code is automatically changed when the alarm sender is carried from one place to another. When an alarm is sent, the latest stored room code is sent by radio to a central alarm receiver. The room code received in the alarm receiver is stored in a memory and the position of the sender is shown on a digital display. How coded messages are sent by radio and received and displayed in a central receiving station is already described in the U.S. Pat. No. 3,678,391.
The room code in the alarm senders is reset as follows: A number of small, locally fixed transmitters, with continuous electromagnetic emission, in this case inductive emission, are placed in a building, and send a code unique for the position of the fixed transmitter to a receiver in each alarm sender, this code therefore being called the room code. The received code is stored in a memory in the sender, and if the sender is triggered for sending an alarm, the stored code is transmitted with the radio signal to the central alarm receiver.
Each fixed transmitter is suitably placed in one door frame so that transmission of the room code takes place when the alarm sender passes through door frames between different rooms. The code transmitted by the fixed transmitter is thus unique for the door frame where the transmitter is placed. The fixed inductive transmitters for the unique code only transmit with low power, and their transmitting antenna is a small magnetic dipole antenna. Since the transmitting power is low and the field strength from a small dipole antenna is, to the first approximation, inversely proportional to the cube of the distance from the antenna, the clear domination of the field strength from a transmitter in a door frame over
REFERENCES:
patent: 3644883 (1972-02-01), Borman et al.
patent: 3864674 (1975-02-01), Worsham et al.
patent: 3914692 (1975-10-01), Seaborn
patent: 3925763 (1975-12-01), Wadhwani et al.
patent: 3973200 (1976-08-01), Akerberg
Crosland Donnie L.
Rubinson Thomas A.
Telefonaktiebolaget L M Ericsson
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