RFL 9780 RFL Electronics Inc.
April 8, 2003 6-21 (973) 334-3100
If however, the trip input was actually noise, the receiver section’s output will return to guard before
the pre-trip timer times out. This condition will trigger the bipolar noise detector, enabling the bipolar
noise timer with its logic-low BNOISE output signal. The bipolar noise timer adds an additional preset
time requirement to that of the pre-trip timer’s preset time requirement. The bipolar noise detector
forces this state for the period of the noise plus an additional 50 ms. Additional noise pulses will re-
trigger and extend the bipolar noise if they occur before the 50 ms time-out. If a trip occurs within 50
ms after the noise pulse, the trip would have to satisfy the combined pre-trip and bipolar time
requirement before being considered a valid trip.
The output signal of the bipolar timer is HAS_TRIPPED. This output can be monitored at edge
connector pin C2.
The bipolar noise detector is also fed to the alarm timer. A bipolar noise condition, which lasts longer
than the preset time of the alarm timer, will result in an alarm output.
6.5.1.9 THRESHOLD DETECTORS
The signal level detector is a window detector that uses two comparators and associated components to
detect signals that are above or below established limits.
If the SIGNAL_ENVELOPE input at edge connector pin C17 exceeds 7.17 volts, the logic-high HI
SIG signal will be fed to the blocking logic circuits. Indicator DS3 will light to indicate an extreme
high-level signal condition.
If the SIGNAL_ENVELOPE input at edge connector pin C17 falls below 0.094 volts, the logic-high
LO SIG signal will be fed to the blocking logic circuits and to the optional unblocking circuit function.
Indicator DS4 will light to indicate an extreme low-level signal condition. A low signal output is
available at edge connector pin C27 (LO_SIG_OUT).
6.5.1.10 CARRIER ENVELOPE NOISE DETECTOR
The carrier envelope noise detector monitors the SIGNAL_ENVELOPE input at edge connector pin
C17 and produces a signal that is applied to the blocking path if a channel is too noisy. It is formed
from three operational amplifiers and its associated components. The carrier envelope noise detectors
are enabled when SW8-1 is placed in the ON position, and are disabled when placed in the OFF
position. The SIGNAL_ENVELOPE input is smoothed by a 50 Hz low-pass filter formed by the first
operational amplifier (U2A). The output of opamp U2A feeds the input of two other operational
amplifiers (U1B and U1C). The SIGNAL_ENVELOPE signal is also directly connected to each of the
operational amplifier’s other input. Both of these operational amplifiers serve as comparators. The
outputs of these comparators form the open-collector active low outputs CE_HIGH and CE_LOW.
If noise is present, it will modulate the SIGNAL_ENVELOPE input, causing its average level to
decrease or increase. If the modulation exceeds the nominal carrier level by 29%, CE_HIGH will go
low indicating high-level carrier envelope noise may be present. If the modulation decreases below the
nominal carrier level by 35%, CE_LOW will go low indicating low-level carrier envelope noise may be
present. CE_HIGH and CE_LOW signals are applied to the blocking logic circuit within the Actel
FPGA for further digital processing.
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