jcb JS300 Service Manual page 503

Hand Throttle Control Unit
The hand throttle control knob 1 operates a potentiometer
2 which gives and analogue output between 0 and 4.5V.
The potentiometer has no stops and the control knob can
turn continuously in both clockwise and anti-clockwise
directions.
When the control knob turns clockwise the output rises
from a minimum of 0V to a maximum of 4.5V. When the
control knob turns anti-clockwise the voltage output falls.
The MECU is programmed not to respond when the output
changes ('flips') from 0 to 4.5V or 4.5 to 0V. The MECU
V
0
Fig 15. Hand throttle potentiometer output / control knob rotation
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Section C - Electrics
Engine and Power Control
Engine Throttle and Power Mode Control
simply detects falling or rising voltage from the
potentiometer. The output from the hand throttle
potentiometer is shown on the graph.
The MECU monitors the rate of change of the hand throttle
potentiometer. When the control knob turns slowly the
MECU responds with fine step changes to the engine rpm
and output to the hydraulic pump proportional solenoid
valve. The knob must rotate 360 degrees to go from
minimum to maximum engine rpm. When the control knob
rotates quickly the engine rpm and pump solenoid outputs
change in large steps. Minimum to maximum engine rpm
only requires the knob to rotate 120 degrees This allows
the operator to choose coarse or fine adjustment of the
machine power setting.
2
0
1
C128340
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