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24
en | Operation
8
Operation
8.1
Line supervision
For loudspeaker line supervision three different options are available. They differ in
performance, cost, and suitability for various applications and situations.
In general the device can detect open circuit and short circuit. In case of an open circuit only a
fault message will be generated. In case of a short circuit a fault message will be generated
and the loudspeaker line will be automatically deactivated to avoid influence to other
loudspeaker lines.
8.1.1
Impedance measurement
The PVA-4CR12 controller provides a function to measure the loudspeaker cable impedance.
This function puts a sinus signal on the loudspeaker cable connection and measures the
effective current and voltage. The impedance value of the loudspeaker cable (= cable and
loudspeaker) is calculated based on the measurement results. Impedance measurement can
only be done in non-active loudspeaker cable outputs.
To detect impedance deviations in the loudspeaker cable, caused by an open or shorted cable
connection, a failure-free loudspeaker cable reference value must have been measured and
stored beforehand. All future impedance measurements are only compared against the
impedance reference value. When an impedance value exceeds the accepted and configured
tolerance, a failure is reported.
The calibration of impedance measurement circuits is not necessary because the system only
notices impedance tolerances. In this way, absolute failures of values are mathematically
eliminated.
The measuring frequency and voltage can vary within given borders and can be adapted to the
local conditions, like used loudspeaker types and cables or mains power. In general, it is
recommended not to deviate from given default values. If the frequency is too high, the
measurement signal might be audible. If the frequency is too low, the measured impedance
value may be outside the specified range as lower frequency decreases the impedance of the
loudspeaker's transformer.
Notice!
Starting with the controller/router version HW: 02/00 (see product label), the measuring
i
generator has a protective circuit with high-impedance resistors to protect against external
voltages. Therefore, the measurement voltage at the outputs of the configured loudspeaker
cable may vary depending on the impedance of the loudspeaker cable.
Loudspeaker cable impedance
The impedance of the loudspeaker cable can be affected by several negative factors:
–
The loudspeaker cables, the transformers and the loudspeaker coils are usually made of
copper. Copper has a temperature coefficient of α = 3.9 1/K.
In other words, the resistance changes by about 4% with a temperature change of 10 °C.
Example:
In a parking garage, the impedance of the loudspeaker cable can change by a factor of about
16% between winter (-10 °C) and summer (+30 °C).
–
A defective loudspeaker might not be detected if long loudspeaker cables with a higher
measuring frequency are used, due to the fact that the cable impedance (or cable
capacitance) might become dominant compared with the loudspeaker impedance.
2022-11 | 07 | F01U306901
Ambient temperature:
Measuring frequency:
User manual
PAVIRO Router
Bosch Security Systems, B.V.
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