MacDon FD75, Operator'S Manual

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Revision B
4.2 Auto Header Height Control Sensor Operation
The sensors that send height signals to the combine are essentially large resistors that allow a position sensor arm to move
and thereby send a position signal to the combine.
1025389
A
B
C
Figure 4.2: Variable Resistor Type Sensor
The position sensors supplied with the auto header height
control system are 1000 ohm (1 k) industrial series variable
resistors. Each sensor consists of a sealed unit with one three-
pin connection point (A) and two mounting holes (B). A signal
wire is connected internally to movable wiper (C), which sweeps
across a high resistance filament band. An external arm is
attached to movable wiper (C) and, as it moves, the wiper
moves across the resistance filament to change the resistance at
the signal wire, which changes the output voltage. The
resistance across the power and ground pins should be
approximately 100 ohms. Normal operating signal voltages are
0.5
–
4.5 VDC or 5
–
95% of available voltage.
•
A sensor operating with a signal voltage below 5% is
considered to be shorted.
•
A sensor with a signal voltage above 95% is considered to
be open.
•
A change in header height will cause the voltage signal to
change.
AUTO HEADER HEIGHT CONTROL