ELECTRICAL SYSTEM MLC300 SERVICE/MAINTENANCE MANUAL
3-18
Published 11-22-17, Control # 257-02
Temperature Sensors
A controller digital output provides power to the temperature
sensor.
The sensor produces an analog output voltage that is
proportional to temperature. A controller analog input reads
this output voltage, and software determines the value of the
load based upon the current level.
Fuel Level Sensor
A controller digital output provides power to the fuel level
sensor. The sensor transducer produces an ultrasonic pulse
that reflects off the fuel surface and bottom of the fuel tank.
A micro-controller in the fuel sensor uses the echo return
times to calculate the distance from the fuel surface to the
bottom of the tank and sends a controller analog input a
voltage that is proportional to the fuel level.
Hydraulic Fluid Level Sensor
A controller digital output provides power to the hydraulic
fluid level sensor. The sensor has a capacitive probe that is
immersed in the hydraulic fluid. The level of hydraulic fluid
determines the capacitance of the probe.
A micro-controller in the probe translates the probe
capacitance to an analog output voltage that is proportional
to the fluid level and sends this to a controller analog input.
Pressure and Vacuum Switches
Pressure and vacuum switches are normally closed. They
open when the vacuum or pressure level exceeds the setting
of the switch. In the non-tripped state, a controller digital
output provides power to the normally closed contact.
A controller digital input reads the applied power through the
normally closed contact back through the center terminal as
a logic high. When the switch is tripped, the normally closed
contact opens, breaking the path of power through the center
terminal, and the controller reads this as a logic low.
Relays
A controller digital output drives the relay coil. The coil
energizes, creating a magnetic field that closes the relay
contacts. Relays use a small control signal to control the flow
of a large current.
Hand Throttle
A controller provides an 8.5 V
DC
supply to a potentiometer
that is connected to the hand throttle. Power is applied
across the potentiometer windings to ground. Moving the
hand throttle moves a wiper across the potentiometer
windings. The voltage provided at the wiper when referenced
to ground is proportional to the hand throttle position and is
sent to a controller analog input.
Foot Throttle
A controller provides a digital output to a potentiometer that
is connected to the foot throttle. Power is applied across the
potentiometer windings to ground. Moving the foot throttle
moves a wiper across the potentiometer windings. The
voltage provided at the wiper when referenced to ground is
proportional to the foot throttle position and is sent to a
controller analog input.
Travel and Free-Fall Brake Pedals
A controller digital output provides power to a potentiometer
that is connected to the pedal. Power is applied across the
potentiometer windings to ground. Moving the pedal moves
a wiper across the potentiometer windings. The voltage
provided at the wiper when referenced to ground is
proportional to the pedal position and is sent to a controller
analog input.
Pump Displacement Controls
Pump flow is both directional and variable, determined by
position and stroke of a proportional solenoid valve. A
controller sends two pulse-width modulated (PWM) output
signals to two coils that actuate the solenoid valve in
opposite directions. As a PWM duty cycle increases at one
coil, more fluid is ported to the swashplate servo pistons
through the solenoid valve, increasing the swashplate angle
in the direction commanded. As the swashplate angle
increases, so does the piston stroke within the pump,
increasing the pump output volume.
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