microcontroller to store the current unity status in the non-
volatile memory. The DC power supply provides input transient
protection to meet RTCA DO-160C power input, voltage spike,
and lightning requirements.
1.10
Status Output
The status output provides a ground output when the freezing rain
sensor is operating correctly, and high impedance (200 K
Ω
minimum) when the unit has detected a failure. Failures are
detected through continuous and initiated tests. The Status output
is capable of sinking 50 mA and is guaranteed to be no more than
1.5 VDC with respect to Signal Return when active. This output
is transient protected to meet RTCA DO-160C lightning
requirements and to prevent stray high-voltage from coupling
into the unit and damaging the output transistor.
1.11
Ice Signal Output
The Ice Signal output provides a ground output for 60 ± 6
seconds when the ice detector has detected the presence of ice
(frequency drop of 130 Hz, equivalent to approximately 0.020”
ice formation). If the frequency subsequently decreases by 130
Hz while the Ice Signal output timer is non-zero, the timer is
reinitialized to 60 seconds.
The output is transient protected to meet RTCA DO-160C
lightning requirements and to prevent stray high-voltage from
coupling into the unit and damaging the output transistor.
The ice output has feedback to the microcontroller for software to
verify it is in the correct state for more built in test coverage. The
software in the 0871KB2 model uses this feedback to verify that
the ice output is operating correctly. However, in the 0871KB1
model, the software does not use this input.
To interface to the 0871 KB, the power supply must provide a
pull-up to 5 to 28 volts. When the ice output is inactive (open),
the nominal resistance to ground is 13.4 K
Ω
. The power supply
should source at least 0.250 mA to provide the proper signal to
the Ice Signal feedback circuitry. When the output is active
(closed), it is capable of sinking 50 mA and is guaranteed to be
no more than 1.5 VDC with respect to Signal Return.
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