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The BMA (Battery Mini Amplifier) is a
battery powered amplifier unit that provides voice
communications and signaling facilities.
An internal
Nickel Metal Hydride battery is trickle charged from a central
power supply unit via an interconnecting cable. It comprises a
steel enclosure which houses two side facing loudspeakers, and
a polycarbonate amplifier unit (BMA Interior). The BMA
Interior includes a microphone behind a grill on the front and
three push buttons. The whole unit is sealed to IP65 to
withstand the underground environment. Cable entries (20mm)
are provided at each side of the unit. Internal connections
are by plugs and sockets for easy maintenance. Stand-alone
voice communication and signaling can be provided by a PSU and
a number of BMAs interconnected by a 3-core cable.
Broadcast Audio
Signals on the Audio
wire that exceed a pre-set threshold are broadcast via the
loudspeakers.
Speak (PTT)
Pressing the Speak
button disables the loudspeakers and enables the microphone.
Speech will be broadcast by any other BMA on
the string,
and passed connection is available.
Call
Local
The Call Local button causes the main system
controller to generate a 2kHz tone for the time that the
button is pressed. The tone will be broadcast by all the BMA
on the string.
Call Exchange
Pressing the Call
Exchange button causes the BMA to generate a 194Hz signal for
5 seconds. The tone will be broadcast by all the other BMAs on
the string, and passed to the surface if a connection is
available, and may be used to establish a surface
call. | 
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