The Plena Voice Alarm System employs a simple and easy to use method of loudspeaker surveillance based on impedance measurement. On long wire runs, external influences, such as cable capacitance and speaker impedance, can negatively influence the reliability of the measurements. The dummy loads provide a filtered load exclusively at the pilot tone frequency.
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This greatly increases the dependability of impedance measurements, providing reliable break or short circuit detection, even on long wire runs.
To improve the performance of the impedance measurement Bosch Security Systems introduced the Plena Dummy Load. It increases the loudspeaker load at the monitored frequency of 20 kHz, while having a minimal load in the normal audio frequency range.
When connected in parallel with the last loudspeaker on a line, it will increase the percentage of impedance present at the end of the line, thus increasing the number of loudspeakers that can be attached. At the same time, it will also increase the margin for masking by cable capacitance, allowing longer cable lengths.
The dummy load connects in parallel to the last loudspeaker on a line, which must be a Bosch loudspeaker with the appropriate mounting studs. It has a jumper to set the load (at 20 kHz) to 8, 20 and 60 W, according to the results calculated by the Dummy Load Calculator.
The Dummy Load Calculator is a spreadsheet that uses macros to calculate whether an application can use a dummy load, and what the optimal load setting would be. The spreadsheet is available from all Bosch dealers.
|Connector||High temp flying leads|
|Voltage||100 V loudspeaker line|
|Load||8, 20 and 60 W|
|Dimensions (H x W x D)||17 x 30 x 50 mm|
|Weight||Approx. 80 g|
|Operating temperature||-10 ºC to +55 ºC (14 ºF to +131 ºF)|
|Storage temperature||-40 ºC to +70 ºC (-40 ºF to +158 ºF)|
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