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Issue 1
BEL1IP LOUDSPEAKER LINE SURVEILLANCE SYSTEM
The BEL1IP is an IP66 rated Loudspeaker Line Termination Unit, which is normally fitted at the end
of the 100V Loudspeaker Line.
Upto four BEL1IP units may be fitted to a single Loudspeaker Line, allowing spurs to be monitored.
The unit generates a small DC current from the 100V line & superimposes this on the loudspeaker
line.
This DC current is monitored by the BVRDACO / BVRDNCO / BVRD2M4 etc . Both the amplifier
and the continuity of the cabling are monitored.
The IP66 rated enclosure has a 25mm gland hole for site cabling, however it is the installer’s
responsibility to ensure a suitable gland is fitted to maintain the IP66 rating.
This system is set to use either 30Hz or 20KHz surveillance tone when installed.
Advantages Disadvantages
30Hz
Surveillance
Frequency
•
Less power absorbed by cable
as compared to 20KHz
•
More positive fault detection as
breaks in the cable are easier to
detect due to lower stray
capacitive coupling compared to
20KHz.
•
Most digital meters selected to
the AC range will accurately
indicate a 30Hz signal.
•
Suitable for systems employing
horn loudspeakers or ceiling
loudspeakers which have a poor
low frequency response
•
Speakers with a good low frequency
response will produce the 30Hz tone.
•
Any harmonic distortion produced by the
amplifier may be audible, even when
produced using horn loudspeakers.
•
Interrupting the 30Hz surveillance tone
will cause a click thus envelope shaping
must be employed.
20KHz
Surveillance
Frequency
•
Generally
inaudible, however
some speakers may produce a
sub-harmonic i.e. 10KHz.
•
Highly capacitive cable such as PYRO,
FP200 etc absorb a lot of power at this
frequency.
•
Breaks in cable may be difficult to
indicate due to the capacitive coupling
between adjacent conductors.
•
Possibility of lines resonating at this
frequency and therefore consuming
unnecessary power
•
Some digital multi-meters will not
accurately read 20KHz AC.
