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.
Pulse Width Modulated Sensors
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| Illustration 1 | g00288430 |
Pulse Width Modulated Signal | |
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| Illustration 2 | g00497140 |
Typical PWM Sensor Circuit | |
Pressure Sensor (Air Inlet)
The air inlet pressure sensor is an input of the Caterpillar Monitoring System. This sensor gives the Caterpillar Monitoring System a value for the air inlet pressure. A gauge displays the status of the pressure. This pressure sensor senses the turbo compressor outlet pressure. The air inlet pressure sensor is a pulse width modulated sensor. This sensor 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 base frequency of the sensor is constant at 500 ± 150 Hz. The signal wire of the air inlet pressure sensor connects to connector contact 27 of the Caterpillar Monitoring System. The sensor is supplied operating power through connector contact "A". Connector contact "A" comes from connector contact 24 of the Caterpillar Monitoring System.
Pressure Sensor (Engine Oil)
The oil pressure is an input of the Caterpillar Monitoring System. The oil pressure sensor tells the Caterpillar Monitoring System the pressure of the engine oil. A gauge displays the the status of the engine oil pressure. This sensor continuously generates a PWM signal. The duty cycle of the PWM signal varies from 10% to 90% in proportion to the oil pressure. The base frequency is 500 ± 150 Hz. The signal wire of the oil pressure sensor connects to connector contact 17 of the Caterpillar Monitoring System. The sensor is supplied operating power through connector contact "A". Connnector contact "A" comes from contact 24 of the Caterpillar Monitoring System.
Pressure Sensor (Fuel)
The fuel pressure sensor is an input of the Caterpillar Monitoring System. The fuel pressure sensor tells the Caterpillar Monitoring System the pressure of the fuel. A gauge is used to display the status of the fuel. The pressure sensor senses the pressure of the fuel. The fuel pressure sensor is a pulse width modulated sensor. This sensor continuously generates a PWM signal. The duty cycle of the PWM signal continuously varies from 10 to 90% in proportion to the air inlet pressure. The base frequency of the sensor is constant at 500 ± 150 Hz. The signal wire is contact "C". The signal wire of the fuel pressure sensor connects to connector contact 38 of the Caterpillar Monitoring System. The sensor is supplied operating power at connector contact "A" from the Caterpillar Monitoring Systemconnector contact 24.
Temperature Sensor (Engine Oil)
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 (+24 DCV). The temperature sensor sends a signal to the main display module which changes as the temperature of the fluid changes. The main display module measures the duty cycle of the sensor signal in order to determine the fluid temperature.
Temperature Sensor (Exhaust)
The exhaust temperature sensor is an input of the Caterpillar Monitoring System. This sensor measures the temperature of the exhaust. A gauge is used to display the status of the exhaust temperature. The exhaust temperature sensor is a pulse width modulated sensor. This sensor continuously generates a PWM signal. The duty cycle of this signal varies from 10 to 90% in proportion to the air inlet pressure. The base frequency of the sensor is constant at 500 ± 150 Hz. Connector contact "C" is the signal wire. The signal wire of the left exhaust temperature sensor connects to connector contact 10. The signal wire of the right exhaust temperature sensor connects to connector contact 8. The sensors are supplied operating power from the Caterpillar Monitoring System (connector contact 24).
Temperature Sensor (Inlet Manifold)
The inlet manifold temperature sensor is an input of the Caterpillar Monitoring System. This sensor tells the Caterpillar Monitoring System the temperature of the inlet manifold. A gauge is used to display the status of the inlet manifold temperature. The inlet manifold temperature sensor is a pulse width modulated sensor. This sensor continuously generates a PWM signal. The duty cycle varies from 10 to 90% in proportion to the inlet manifold temperature sensor. The base frequency of the sensor is constant at 500 ± 150 Hz. Connector contact "C" is the signal wire. The signal wire of the inlet manifold temperature sensor connects to contact 28 of the Caterpillar Monitoring System.
Speed Sensor (Engine)
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| Illustration 3 | g00497032 |
Speed Sensor (1) Sensor. (2) Connector. | |
Speed sensor (1) is a frequency sensor. Speed sensors are 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 frequency of the sender at a rate of one pulse per gear tooth. The main display module then determines the engine speed. Next, the main display module shows the engine speed.
The engine speed sensor is located on the flywheel housing.
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| Illustration 4 | g00311291 |
Magnetic Speed Pickup (MPU) | |
The magnetic speed pickup (MPU) sends a signal that represents the speed of the engine to the control board and to 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. A positive voltage is generated when each tooth goes by the pole piece. A negative voltage is generated when each space between the teeth goes by the pole piece. The control board counts the frequency of this speed signal. The control board determines the speed of the engine.
Liquid Level Sensor (Engine Coolant)
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| Illustration 5 | g00506216 |
Coolant Loss Sensor | |
The optional engine coolant loss sensor sends a battery negative signal to the control board when the coolant level is low. This signal connects to the spare fault input that is located on the control board. The spare fault is programmable. The spare fault can be either an alarm fault or a shutdown fault. A battery negative signal causes the control board to perform the preselected type of fault, alarm or engine shutdown. The sensor is mounted on the top of the engine radiator. The exact location depends on the engine model.
The sensor sends an open signal "B+" from connector contact "C" to the control board when the coolant is at a normal level. The sensor sends a battery negative signal from connector contact "C" to the control board when the coolant level is low. The sensor is supplied operating power at connector contact "A" and connector contact "B". Connector contact "A" is connected to "B+". Connector contact "B" is connected to the battery negative terminal.