R
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13
Chapter 2
Technical Description
The optional waveguide pressure switch is used to monitor a pressurized
system of waveguide or air dielectric coaxial cable feedlines.
The seven (7) uncommitted (user-defined) alarm inputs are brought into
the transmitter via a set of terminal blocks. Contact closure on these
differential inputs indicates an alarm condition.
Four analog voltage sources are monitored through a use of multiplexed
A/D (Analog to Digital) converters in the microcontroller. Battery capacity
is a function of both voltage and temperature. Therefore, the four sources
represent two battery voltages and the battery temperature readings are
reported for evaluating the charge capacity left in the batteries.
The four analog voltage sources are also wired to the user connectors.
The fourth analog input can monitor a voltage level from 0 V to 30 V.
There are two user interface connectors that permit standard supervisory
equipment access to the 27 opto-couplers which correspond to the 27 digital
inputs. Each opto-coupler consumes a maximum of 10 mA of current upon
closure. This feature is field-strappable for applications where there is concern
about the current consumption of the opto-couplers.
2.3.1 Transmitter Alarm LEDs
Each of the system’s 20 predefined digital inputs activates an LED on the
transmitter when an alarm triggers. The summary LED indicator on the
transmitter will activate if any of the 27 alarm inputs, predefined or uncommitted,
triggers. LEDs remain lit as long as an alarm is active.
To test the LEDs, press the button on the far lower left side of the transmitter. All
alarm LEDs will light while the button is pressed (lamp test). After a short time,
only those LEDs indicating an alarm condition will remain lit, all other LEDs will
be dark.
2.3.2 Standard Alarm Data Transmission
The RMAS-120 transmits the alarm data stream in sequential frames (96 bits)
with four frames per each complete data sequence. Each frame contains 27 bits
for the digital alarm inputs, 32 bits for the A/D telemetry (4, 8-bit channels), and
37 framing bits for receiver synchronization. In data transmissions, there is a
1 dB peak-to-peak amplitude modulation of the microwave carrier which
corresponds to 1 dB/10 ms (100 dB/second) amplitude transition time. This
modulation ensures compatibility with any microwave radio AGC that can track
the 100 dB/second standard fast fade rate.
The transmitter output is a balanced output pair of 2 V, peak-to-peak. This signal
feeds to the PIN diode modulator in each amplifier to modulate the amplitude of
the microwave carrier by 1 dB, peak-to-peak.
Serial transmission data is Manchester or Bi-Phase encoded, creating a clock
transition in the middle of each data bit for error reduction purposes. Once
