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«Our design organization is selecting an emergency voice notification system for a large shopping center. According to the standards, the designed system must ensure control of the serviceability of the speaker connection lines. Previously, we used warning equipment with various methods of line integrity control in projects: by measuring impedance, by measuring the line current load, by pilot tone, etc. But these methods have a number of limitations and are not always suitable for complex multi-zone systems where it is necessary to control a large number of lines with different loads. In addition, speaker connection cables can be laid with branches and it is unclear how to control the integrity of the branches. Tell me, what modern technologies can be found on the market that allow you to economically solve the problem of line control? — Boris Golubtsov, St. Petersburg.»
Sergey KUZNETSOV, Director of Distribution, Technical Support and Marketing for Bosch Security Systems Russia – Ukraine – Belarus – Kazakhstan, answers the reader’s question.
To solve this problem, you can use systems that implement a high-frequency control signal (pilot tone) detection method. The fact is that the method for measuring the impedance of loudspeaker lines does have limitations in terms of the connected load, line length, is not always accurate, and, what is most unpleasant for the user, during the measurement process, weak clicks are heard and the background music stops broadcasting. In this case, connecting additional loudspeakers to the line requires re-calibration of the monitoring system. Currently, there are systems on the market that use the pilot tone transmission and reception method, but often the control terminal devices at the end of the line issue a relay response in the event of line damage, which means that return cables are required to transmit information to the central system. At large facilities, this can lead to considerable expenses for additional cables. The most economical way is to use systems where the control signal is transmitted via the same wires that connect the loudspeakers. Also use addressable control terminal boards, which allow you to control branches from the line and more quickly eliminate faults at the facility.
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