Baldwin Boxall BEL1IP User manual
Baldwin Boxall Communications Ltd.
Wealden Industrial Estate, Farningham Road
Crowborough, East Sussex, TN6 2JR
Telephone: 01892 664422
Fax: 01892 663146
Website: www.baldwinboxall.co.uk
Email: mail@baldwinboxall.co.uk
BEL1IP
06/12/2010
Issue 1
ECR DP310
BEL1IP
Operating Instructions
- 2 - 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.
- 3 - Issue 1
Technical Description
The surveillance tone is fed (via the power amplifier) to the loudspeaker line.
At the end of each line (or at the end of each spur on that line) a BEL1IP detects this signal and
super imposes a DC current with reference to ground.
Where there are no spurs on the line the single BEL1IP is set to produce 1mA. When there are
spurs, the BEL1IP units are set to produce a total current of 1mA. Eg If there are two spurs each
unit is set for 0.5mA. This current is monitored by the Fault Detection module.
The constant current source is designed so that if one side of the line becomes disconnected no
current flows.
A voltage doubling circuit is incorporated which improves the overall system sensitivity, and
care must be taken as high voltages may exist.
The recommended surveillance tone level is 10 Volts but detection is not affected when higher
speech or music signals are present. The DC line current produced by the BEL1 is extracted by the
centre tap of the amplifier's output transformer, which is fed to the input of the fault detector. This
input is terminated with a 6.8K resistor and assuming a line current of 1mA produces 6.8 Volts
across it. This DC signal is buffered and fed into a window detector via a sample and hold gate.
The lower voltage threshold is 5 Volts and the upper is 10 Volts and providing the input signal is
within this range the fault detector will indicate a normal condition. The input circuit also includes an
AC detector providing a fault condition should the loudspeaker line be unbalanced due to a fault
condition.
Switch Settings
The switches on the unit are set depending on the number of spurs and hence BEL1IPs on the line,
as shown in the following table.
SW1
1 2 3 4
1 on * on * on * on *
2 off on off on
3 on off on off
No. of spurs
on line
4 off off off off
* Default as supplied from the factory is for a single spur and a single BEL1IP per line.
- 4 - Issue 1
Internal View of BEL1IP
Typical Connection details for BEL1IP
