Description
A Plena end-of-line board is a printed circuit board (PCB) engineered for the detection of a 20 kHz pilot tone produced by a supervised public address system or voice alarm system. In the presence of this pilot tone signal exceeding 5 V, it activates a voltage-free switch and illuminates an LED for straightforward visual confirmation. These end-of-line boards are critical for monitoring the continuity of the pilot tone within a loudspeaker line. Positioned at the terminus of a loudspeaker line, they detect the presence of the consistent 20 kHz pilot tone—a tone that remains undeviating whether background music (BGM) is playing, during active calls, or even without any signal. This tone, being inaudible and at a subdued intensity (-20dB), ensures it doesn’t interfere audibly. The illumination of an LED and closure of a contact occur when the pilot tone is present; conversely, the absence of tone results in the contact opening and LED extinguishing. This functionality, when mounted at the loudspeaker line’s endpoint, reflects the integrity of the entire audio line. The detection of the pilot tone signal operates independently of the number and load of loudspeakers on the circuit or the line’s capacitance. The contact switch can interface with various public address systems, such as the Bosch Voice Alarm System, to signal and report anomalies on a loudspeaker line. Multiple end-of-line boards can be interconnected, or daisy-chained, to a singular fault input to effectively monitor loudspeaker lines with multiple branches. Since the background music also carries a 20 kHz pilot tone signal, there is no disruption required for the BGM.
