Furuno FR-2155, Service Manual

Page: 34 / 152

2-20
2.20 ARPA target acquisition and Tracking
4. Conditions for manual acquisition
The target can be acquired manually under the following conditions.
1) An echo from target must be received for three consecutive sweeps and scans within the acquisition
area.
2) The target echo must be smaller than the and echo data (at the front end processor).
3) A target must be within the acquisition area : 0.2 to 32 nm.
4) The ARPA can acquire 30 targets. All 30 may be acquired manually, or 10 manually and 20 auto-
matically.
5) No signal error (TRIG, HD, BP, VIDEO, gyro) shall be detected.
5. Conditions for automatic acquisition
The target can be acquired manually under the following conditions.
1) An echo from target must be received for three consecutive sweeps, and seven consecutive scans
within the acquisition area.
2) The target echo must be smaller than land echo data (at the front end processor).
3) The target must be within acquisition area: 0.1 to 32 nm (or 24 nm) depending on initial setting.
Target echoes behind a land echo within the acquisition area cannot be acquired automatically.
4) 20 targets can be automatically acquired.
5) No signal error (TRIG, HD, BP, VIDEO, gyro) shall be detected.
6. Automatic tracking
1) A tracked target is judged as a lost target when no return is received for nine consecutive scans.
When the system detects a lost target, “LOST TARGET” appears on the display and the ARPA
symbol blinks.
2) A lost target will be reacquired and tracked when acquisition condition again becomes satisfactory.
3) Automatic tracking is discontinued when the target moves out of the acquisition range (less than 0.1
nm or greater than 32 nm).
4) An acquired and tracked target which moves behind a land echo will be declared as a lost target.
2.21 ARPA Land Discrimination
A target is recognized as a landmark and not acquired if it is bigger than the preset value in range
or bearing direction. The preset value is entered though the ARPA Initial setting menu.