56 Functional Description TB8100 Installation and Operation Manual
© Tait Electronics Limited June 2005
The PA and PMU sections on Figure 4.13 show most of the monitored
parameters in each module and the control outputs from the
microprocessors, which are also available to the reciter RISC via the I
2
C bus
and form the basis of the TB8100 monitored alarms.
Each reciter, PA and PMU module also stores the following information
specific to that module:
■ calibration parameters
■ serial and product number
■ factory configuration.
This ensures that the module is a true entity in its own right, thus helping
to support simple ‘plug and play’ site module replacement procedures.
The TB8100 control panel provides several important functions.
Depending on the control panel version these functions include, but are not
limited to, the following:
■ an interface point to monitor and respond to failure alarm outputs from
the fans
■ a point to read key presses and display base station status on output LEDs
■ speaker control and amplifier for on-site monitor audio.
All control panel logic inputs and outputs are implemented by using an I
2
C
port expander that performs a serial (I
2
C) to parallel conversion (and vice
versa) over the I
2
C bus. The control panel port expanders are fixed address
8-bit input and output interfaces. The heaviest user of the I
2
C bus is actually
the control panel keypad read polls which occur on average every 50ms.
4.7 Fan Operation
The cooling fans are mounted on the front panel. One fan is in front of the
PA and another in front of the PMU. The fans do not operate continuously
but are switched on and off as needed by the reciter firmware. When the
base station is switched on, both fans come on for a short time and are then
normally switched off. The operation of the PA fan is configurable via the
Service Kit but the PMU fan is not. It has fixed on/off thresholds and a
defined set of duty cycles based on the PMU temperature, as follows:
PMU Temperature Duty Cycle
<65°C (<149°F) Increases with increasing current draw
65°C to 75°C (149°F to 167°F) On two minutes, off one minute
>75°C (>167°F) Always on
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