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Alarm system
| Details |
Inventors: Scheidweiler, Andreas;
Assignee: Cerberus AG (CH)
Primary Examiner: Chapman; John
Assistant Examiner:
Attorney, Agent or Firm: Brumbaugh, Graves, Donohue & Raymond
In an alarm system with a number of alarm devices such as fire intrusion alarm devices connected to a signal center, upper and a lower thresholds are defined in the alarm devices, with the inactive value of the sensor output signal located between the threshold limits. The alarm devices transmit one of three indication signals to the signal center depending on whether an alarm sensor output is above an upper limit, below a lower limit or between the upper and lower limits, with these alarm state signals being produced by threshold detectors. Also, it is possible to adjust the two threshold limits of the alarms to compensate for changing ambient conditions over extended periods of time. When the sensor output signal reaches one of the upper or lower thresholds both the upper and lower threshold limits either move up or down, respectively, so that the sensor output signal is once again located between the upper and lower threshold limits. The signal center receives the outputs of the threshold detectors and differentiates between five different states, namely the alarm states "normal," "warning," "alarm," "maintenance" and "malfunction", on the basis of the frequency and the type of these signals. |
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DETAILED DESCRIPTION It is the purpose of the invention to create an alarm system which avoids the disadvantages mentioned above, which makes it possible to adapt two "event" thresholds of the alarm devices to changing ambient conditions over extended periods of time, to monitor the inactive value of the sensor output signal and which makes it possible to differentiate between rapid signal changes (fire, intrusion) and slow changes (drift of the inactive value) by the transmission of a maximum of three states.
A further purpose of the present invention is to create an alarm system in which there is a differentiation in the signal center between the warning state and the alarm state when there are rapid signal changes, with the warning state characterizing a lesser danger than the alarm state.
Another purpose of the present invention is to create an alarm system which gives off a maintenance alarm if the drift of the inactive value exceeds a predetermined initial value, and which gives off a malfunction alarm if the output signal of a sensor deviates so far from the inactive value that the alarm device ceases to be able to function.
According to the invention, an alarm system is provided comprising a signal center and a plurality of alarm devices connected to the signal center.
Each alarm device comprises sensor means for producing an electrical signal having a characteristic indicative of a monitored condition and threshold detection means for comparing the electrical signal characteristic to minimum and maximum limits, and for producing an inactive indication signal when the characteristic is between the minimum and maximum limits, a below indication signal when the characteristic is below the minimum limit and above indication signal when the characteristic is above the maximum limit.
Each alarm device also comprises converter means for transmitting the indication signals to the signal center, and switching means for increasing and decreasing both limits of the threshold detection means in response to above and below indication signals, respectively, whereby the minimum and maximum limits are adjusted to compensate for ambient conditions
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