Frequency - The frequency (Hz) varies as the condition changes.
Pulse width modulated - The frequency of this signal is constant. The duty cycle varies as the condition changes.
Frequency Sensors
Frequency sensors produce a signal that varies with the frequency (Hz) as conditions change.
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| Illustration 1 | g00288428 |
Engine Speed and Transmission Speed Sensors | |
The engine speed sensors and the transmission speed sensors are inputs of the power train ECM. These sensors allow the power train ECM to determine the engine and transmission speed. The power train ECM uses this information in order to make shifting decisions. The power train ECM uses this information in order to make decisions on ride control. Refer to System Operation, "Normal Operation" for more information about "Ride Control Operation" and "Transmission Operation". The power train ECM also sends the engine speed information to the Caterpillar Monitoring System on the CAT data link.
The engine speed sensor and the transmission speed sensors are used to measure engine speed and transmission output speed. The speed sensors are frequency sensors. Frequency sensors produce a signal that varies in frequency (Hz) as the condition changes. The frequency sensors generate a sine wave signal that is created by the gear teeth as the teeth pass the sensor. The sine wave signal is sent to the power train ECM. The power train ECM measures the frequency of the signal in order to determine the engine speed and transmission output speed. The engine speed sensor connects to connector contact J2-23 and connector contact J2-29 of the power train ECM. The transmission speed sensor connects to connector contact J2-14 and connector contact J2-20 of the power train ECM.
Pulse Width Modulated Sensors (PWM)
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| Illustration 2 | g00288430 |
Pulse Width Modulated Signal | |
Pulse width modulated sensors produce a digital signal of the duty cycle that varies as the conditions change. The frequency remains constant.
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| Illustration 3 | g00329095 |
Transmission Oil Temperature Sensor | |
The transmission oil temperature sensor is a pulse width modulated sensor. The power train ECM measures transmission oil temperature with the transmission oil temperature sensor. The power train ECM uses the oil temperature reading to adjust the shift time of the transmission. The power train ECM adjusts the shift time of the transmission in order to provide smooth shifts over the various ranges of the transmission oil temperature.
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| Illustration 4 | g00772626 |
Position Sensor (Left Pedal) | |
The left pedal position sensor sends an input to the ECM. The sensor will continuously update the ECM on the position of the left pedal. The operator changes the left pedal position in order to send an output signal to the transmission. The ECM records the change of position. Then, the ECM activates the appropriate solenoid valve.
The left pedal position sensor is a PWM sensor. The sensor continuously generates a PWM signal. The duty cycle varies in proportion to the position of the left pedal. The ECM receives the PWM signal from the position sensor. The ECM measures the duty cycle in order to determine the position of the left pedal. The frequency of the sensor signal is constant at 5000 Hz. The machine electrical system provides +battery voltage to the lever position sensor for operating power.