Senders
Fuel Level Sender
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| Illustration 1 | g01952633 |
Fuel level sender | |
The ultrasonic fuel level sensor determines the fuel level by calculating the time light takes to reflect between the float bottom and the sensor.
Higher the fuel level - More time taken for light to reflect back to the sensor.
Lower the fuel level - Less time taken for light to reflect back to the sensor.
The fuel level sensor is monitored by the Chassis ECM which sends a signal to the Advisor. The Advisor then provides a signal to the analog type fuel level gauge.
The performance screen in the Advisor also displays a digital readout showing the percentage of fuel remaining.
Engine Coolant Temperature Sender
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| Illustration 2 | g00496856 |
Engine coolant temperature sender | |
The engine coolant temperature sender is used to operate the water temperature gauge on the panel. The sender uses variable resistance, proportional to the coolant temperature. As temperature increases, the resistance of the sender decreases. The increasing and decreasing resistance controls the flow of electrical current in the gauge and the sender circuit. The value that is showing on the gauge reflects the amount of current flowing in the circuit. The sender and the gauge are matched to work together as a unit.
Hydraulic Oil Temperature Sender
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| Illustration 3 | g03470096 |
Temperature sender (1) Schematic symbol (2) Sender | |
The temperature sender senses the temperature of fluids. A resistive signal which corresponds to the temperature of the fluid is sent from the sender to the main display module. The typical resistance of the sender is 70 to 800 Ω. The main display module measures the value of the resistance to determine the fluid temperature.
Sensors
Sensors provide information to the main display module about changing conditions, such as speed and temperature. The sensor signal changes in a proportional manner to reflect the condition. The main display module shows the sensor information on the gauges. The recognized sensor signals are:
Frequency - The sensor produces an AC signal with a frequency (Hz) that varies as the condition changes.
Pulse Width Modulated - The sensor produces a digital signal with a duty cycle that varies as the condition changes. The frequency of this signal is constant.
Speed Sensor
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| Illustration 4 | g03470097 |
Speed sensor (3) Sensor (4) Connector | |
Speed sensors are frequency sensors used to measure engine rpm. The sensor generates an AC signal from passing gear teeth, which is sent to the main display module. The main display module measures the sender frequency at a rate of one pulse per gear tooth. The main display module then determines and displays the engine speed.
The engine speed sensor is located on the flywheel housing.
Pulse Width Modulated Sensors
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| Illustration 5 | g00288430 |
Pulse width modulated signal | |
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| Illustration 6 | g00497140 |
Typical PWM sensor | |
Pulse width modulated sensors produce a digital signal. The duty cycle of the digital signal varies as the condition changes, but the frequency remains constant.
Engine Speed Sensor
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| Illustration 7 | g00311291 |
Magnetic pickup (MPU) | |
The magnetic pickup (MPU) sends a signal that represents the speed of the engine to the control board and the tachometer. The MPU is located on the engine flywheel housing. The MPU is a single-pole permanent magnetic generator that is made of wire coils around a permanent magnet pole piece. As the teeth of the flywheel ring gear go through the magnetic lines of flux around the pickup, an AC voltage is generated.
Positive voltage - Is generated when each tooth goes by the pole piece.
Negative voltage - Is generated when each space between the teeth goes by the pole piece.
A control board counts the frequency of this speed signal. The control board determines the engine speed.
Air Inlet Pressure Sensor
The air inlet pressure sensor gives the monitoring system a value for the air inlet pressure. A gauge displays the status of the pressure. The air inlet pressure sensor is a pulse width modulated sensor that continuously generates a PWM signal. The duty cycle of the PWM signal varies from 10 to 90% in proportion to the air inlet pressure. The sensor base frequency is constant at 500 ± 150 Hz.
Temperature Sensor
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| Illustration 8 | g03470098 |
Temperature sensor (5) Sensor (6) Connector | |
Temperature sensor reacts to the temperature of fluids such as engine oil or engine coolant. The sensor receives operating power from the main display module (+8 DCV) or from the battery (+12 DCV). The temperature sensor sends a signal to the monitoring system which changes as the temperature of the fluid changes. The main display module measures the duty cycle of the sensor signal to determine the fluid temperature.
Switches
Switches provide information (input) to the main display module. Switches are the following two state devices:
Closed - The switch connects the control input to the ground.
Open - The switch does not connect the control input. The input is floating.
During normal operation, all switches are closed. When a condition exceeds the trip point of the switch, the switch opens. The open tells the main display module of the abnormal condition. The main display module goes into warning operation, notifying the operator of the abnormal condition.
Key Start Switch
When the key start switch is in the ON position, electrical power from the batteries is supplied to the electronic control modules (ECMs).
When the key start switch is in the STARTkey start switch
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| Illustration 9 | g00927534 |
Key start switch | |
Engine Coolant Temperature Switch
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| Illustration 10 | g00496872 |
Engine coolant temperature switch | |
The engine coolant temperature switch sends a B− signal to the control board when the coolant temperature exceeds the trip point of the switch. This signal causes the control board to perform an engine shutdown for a high water temperature fault. The switch is mounted in the water jacket usually near the front of the engine, the exact location depends on the engine model.
The switch has normally open and normally closed contacts. Only the normally open contacts "A" and "B" are used. Contact "A" connects to the control board. Contact "B" connects to the negative battery terminal.
Engine Oil Pressure Switch
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| Illustration 11 | g00496875 |
Engine oil pressure switch | |
The engine oil pressure switch sends a B− signal to the control board when the oil pressure drops below the trip point of the switch. The B− signal causes the control board to perform an engine shutdown for a low oil pressure fault. The switch is mounted on the outside of an engine oil gallery, the exact location depends on the engine model.
The switch has normally open and normally closed contacts. Only the normally closed contact "A" and contact "C" are used. Contact "C" connects to the control board. Contact "A" connects to B−.
The specifications for the 3E-6455 Pressure Switch are:
- Pressure for actuation is 90 ± 21 kPa (13 ± 3 psi).
- Pressure for de-actuation is 70 ± 21 kPa (10 ± 3 psi).
Hydraulic Oil Filter Switch
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| Illustration 12 | g03470100 |
Hydraulic oil filter switch (7) Switch (8) Schematic symbol | |
Switch is open during normal operation. This switch closes to ground when the hydraulic oil filter pressure is greater than the specified value for the switch. The closed switch tells the monitoring system that the hydraulic oil filter is restricted. The switch is open when the switch is off the machine.
Alternator
The monitoring system monitors the frequency at the alternator "R" terminal. The frequency tells the monitoring system if the alternator is rotating.