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. This greatly
increases the dependability of impedance measurements,
providing reliable break or short circuit detection, even on
long wire runs.
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
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.