PISTON ASSEM. 6H6745 - Caterpillar

General Information
Sensors provide information (input) to the main display module about changing conditions. The sensor signal changes in a proportional manner in order to reflect the changing condition. The main display module shows the sensor information on the gauges. The main display module recognizes two types of sensor signals.Frequency - The sensor produces an AC signal. The frequency (Hz) will vary as the condition changes. Pulse width modulated - The sensor produces a digital signal. The duty cycle will vary as the condition changes. The frequency of this signal is constant.Frequency Sensors
Frequency sensors produce an AC signal. The frequency (Hz) will vary as the condition changes. Speed Sensor
Illustration 1 g00304924
Speed Sensor
(1) Sensor. (2) Schematic symbol.
Speed sensor (1) is a frequency sensor. Speed sensors are used in order to measure engine RPM. The Speed sensors are also used in order to measure the machine MPH (km/h). The sensor will generate an AC signal. The sensor recognizes the gear teeth as the teeth are passing. The signal is sent to the main display module. The main display module measures the sensor frequency (one pulse per gear tooth). The main display module then determines the signal that is being processed. The main display module displays either the engine speed or the machine speed. The engine speed sensor is located on the flywheel housing. The machine speed sensor is located at the output end of the transmission housing. Pulse Width Modulated Sensors (PWM Sensors)
Illustration 2 g00304925
Pulse Width Modulated Signal
Illustration 3 g00304926
Typical PWM Sensor Schematic
A PWM sensor produces a digital signal. The duty cycle of the signal varies as the condition changes. The frequency remains constant. Temperature Sensor
Illustration 4 g00304927
Temperature Sensor
(1) Schematic symbol. (2) Sensor.
Temperature sensor (2) reacts to the temperature of the fluids. Examples of the fluids are hydraulic oil, power train oil, and engine coolant. The sensor receives operating power from the main display module (8 DCV) or from the battery (24 DCV). The main display module receives a PWM signal from the sensor. The PWM signal will change as the fluid temperature changes. The main display module measures the duty cycle of the sensor signal in order to determine the fluid temperature.Fuel Level Sensor (Ultrasonic Type)
Illustration 5 g00304928
Fuel Level Sensor (Ultrasonic Type)
(1) Schematic symbol. (2) Float. (3) Guide tube. (4) Sensor.
The fuel level sensor (4) reacts to the level of the fuel in the fuel tank. The fuel level sensor (4) emits an ultrasonic signal. The signal is emitted up the guide tube (3). The ultrasonic signal is reflected off a metal disk on the bottom of float (2) and the signal returns to the sensor. The sensor measures the time that is required for the ultrasonic signal to travel from the sensor to the float and then back to the sensor. The sensor also measures the level of the fuel. The open status or the grounded status of contact 3 tells the sensor whether the sensor is installed in a deep tank or the sensor is installed in a shallow tank. Contact 3 is