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The ARPA system provides the following alarms:
Dangerous target alarm CPA/TCPA
Guard zone entry alarm GZ
Lost target alarm LOST
System function alarm ARPA (DATA)
Gyro set alarm SET GYRO
……Dangerous Target Alarm: CPA/TCPA………………………………
In the ARPA system, targets are categorized into two types: tracked targets and dangerous targets.
The grade of danger can easily be recognized on the display at a glance. So the officer can easily decide
which target he should pay attention to.
The types of target and alarm are shown below.
Dangerous Target Alarm
CPA LIMIT and TCPA LIMIT: The Setting Values
5.7 ALARM DISPLAY
Status
Tracking target
Dangerous
target
Symbol on
CRT
Alarm
characters
(OFF)
CPA/
TCPA
Alarm sound
(OFF)
Beep sound (pee-poh)
Acknowledgeable
Conditions
• CPA > CPA LIMIT
• 0 > TCPA
• TCPA > TCPA LIMIT
• CPA≤CPA LIMIT,
• 0≤TCPA≤TCPA LIMIT
If either of CPA LIMIT or TCPA LIMIT is set to zero, the dangerous target alarm will
not operate.
Since these alarms may include some errors depending on the target tracking conditions,
the navigation officer himself should make the final decision for ship operations such as
collision avoidance.
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