Husqvarna Automower 420 Technical Manual page 56

5.1.3 Sensors
The robotic lawnmower is equipped with the follow-
ing sensors:
• Front collision sensor (1)
• Rear collision sensor (2)
• Tilt sensor (3)
• Lift sensors (4)
• Rear loop sensors (5)
• Front loop sensors (6)
• Cutting height sensor (7)
• Ultrasonic sensor (450X only) (8)
The tilt sensor and the rear loop sensors are fitted
on the main circuit board in the lower section of the
chassis. The other sensors are fitted to their own
small circuit boards.
The sensors cannot be repaired. If troubleshooting
shows that one of the sensors is faulty, the entire
circuit board (depending on which sensor is faulty)
must be replaced.
The task of the loop sensors is to measure the sig-
nals the circuit board in the charging station sends
along the boundary wire (A signal), the guide loops
(guide signals) and the antenna plate (F and N sig-
nals). The signals are used to control the mower
and keep the mower inside the working area.
The lift sensors and the collision sensors measure
the magnetic field from the 2 permanent magnets
that are located in the body. If the magnetic field
decreases (the distance to the magnet increases)
the main circuit board interprets that the mower has
been lifted or a collision has occurred.
The tilt sensor is an accelerometer positioned on
the main circuit board. It measures the gradient in
both X and Y axis. The value is used, among other
things, to correct the speed of the drive wheels
when mowing on steep slopes.
The current value from the sensors can be read in
the display on the mower, as well as in Autocheck
EXP.
The ultrasonic sensors (450X only) are used to
read off the distance to obstructions in front of the
mower. If an obstruction is detected, the mower will
slow down before it collides with it. The signals are
received by the sensors located in the body and are
processed by the sensor board inside the chassis.
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5. REPAIR INSTRUCTIONS
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