The sensors also enable the ECM to activate alarms, derates, and shutoffs in response to abnormal operation. The functions of the sensors are described below.
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| Illustration 1 | g01096774 |
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Right view A 20 cylinder engine is shown. The sensors have the same locations on 16 cylinder engines. (1) Pressure switch for the engine's coolant (inlet) (2) Detonation sensor (3) Electrohydraulic actuator's pressure switch (4) Engine coolant temperature sensor (5) Manifold air temperature sensor | |
Pressure switch for the inlet of the coolant (1) - A pressure switch is located at the inlet for the engine jacket water. If the inlet pressure is too high, the switch will activate a shutdown. To observe the status of the switch, use the Caterpillar Electronic Technician (ET) to view the "Engine Coolant Pump Pressure" parameter.
Detonation sensors (2) - The detonation sensors monitor the engine for mechanical engine vibrations. Each sensor monitors two cylinders. The sensor produces a voltage signal that is proportional to the engine detonation. If detonation occurs, the ECM can retard the ignition timing in order to reduce detonation. Refer to , "Ignition System". To observe the value of the output of the sensors, use Cat ET to view the "Cylinder #X Detonation Level". The "X" is the number for the particular cylinder.
Electrohydraulic actuator's pressure switch (3) - The electrohydraulic actuator has a pressure switch for the oil supply. Insufficient oil pressure will activate an engine shutdown. To observe the status of the switch, use Cat ET to view the "Hydrax Oil Pressure Switch Status".
Engine coolant temperature sensor (4) - The temperature sensor is located in the water temperature regulator housing. To monitor the coolant temperature, the element must be in contact with the coolant. Otherwise, the sensor will not function properly. A high coolant temperature will activate an alarm or a shutdown. A low coolant temperature will only activate an alarm. The trip points for the activation can be programmed with Cat ET. The engine can be restarted after a shutdown due to high engine coolant temperature. However, another shutdown will occur after one minute if the temperature remains high. To observe the value of the output of the sensor, use Cat ET to view the "Engine Coolant Temperature" parameter.
Manifold air temperature sensor (5) - A sensor for monitoring the manifold air temperature is located in the inlet elbow for the number one cylinder head. Excessive manifold air temperature can activate an alarm or a shutdown during high load or low load operation. The trip points for activation can be programmed with Cat ET. To observe the value of the output of the sensor, use Cat ET to view the "Inlet Air Temperature" parameter.
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| Illustration 2 | g01096853 |
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Left view A 20 cylinder engine is shown. The sensors have the same locations on 16 cylinder engines. (6) Pressure sensor for unfiltered oil (7) Pressure sensor for filtered oil (8) Manifold air pressure sensor (9) Engine coolant pressure sensor (outlet) (10) Engine oil temperature sensor (11) Humidity sensor (12) Speed/timing sensor (13) Atmospheric pressure sensor (14) Oxygen sensor (15) Buffer for the oxygen sensor | |
Oil pressure sensors (6) and (7) - The engine oil pressure is measured before the oil filters (6) and after the oil filters (7). An alarm or a shutdown can be activated by any of the following occurrences: low filtered oil pressure, low oil filter differential pressure and high oil filter differential pressure. The trip point for the activation of a warning or a shutdown for oil filter differential pressure can be programmed with Cat ET. To observe the value of the output of the sensor, use Cat ET to view the "Engine Oil Pressure" or the "Unfiltered Engine Oil Pressure" parameter.
Coolant pressure sensor (8) - A pressure switch is located at the outlet for the engine jacket water. If the outlet pressure is too low, the control system will activate a shutdown.
Manifold air pressure sensor (9) - The sensor for inlet manifold air pressure is connected to the air inlet manifold. The sensor monitors the absolute manifold air pressure. This is the atmospheric pressure plus the gauge pressure. The information is used by the control system to calculate the airflow. To observe the output value of the sensor, use Cat ET to view the "Inlet Manifold Air Pressure (abs)" parameter.
Engine oil temperature sensor (10) - An oil temperature sensor measures the engine oil temperature. A high oil temperature will activate an alarm or a shutdown. The trip points can be programmed with Cat ET. To observe the output value of the sensor, use Cat ET to view the "Engine Oil Temperature" parameter.
Speed/timing sensor (11) - The engine speed/timing sensor is located on the rear end of the left camshaft. The engine speed/timing sensor is monitored in order to determine the position of the crankshaft and the engine rpm. The control system uses the position of the crankshaft to determine the ignition timing. To observe the engine speed in rpm, use Cat ET to view the "Engine Speed" parameter.
Humidity sensor (12) - The humidity sensor is not installed on all engines. If the engine uses oxygen feedback in order to control the air/fuel ratio, the humidity sensor provides atmospheric compensation. There are two possible locations for the installation of the sensor. The sensor may be installed in an inlet air line or inside the housing for the air cleaner. The sensor generates a digital signal that is proportional to the specific humidity of the inlet air. The signal is used for adjusting the air/fuel ratio in order to maintain the level of emissions that is desired. To observe the output value of the sensor, use Cat ET to view the "Specific Humidity" parameter.
Atmospheric pressure sensor (13) - The atmospheric pressure sensor is not installed on all engines. If the engine uses oxygen feedback in order to control the air/fuel ratio, the atmospheric pressure sensor provides atmospheric compensation. The sensor monitors the atmospheric pressure. The control system uses the signal to adjust the air/fuel ratio in order to maintain the level of emissions that is desired. To observe the output value of the sensor, use Cat ET to view the "Exhaust Back Pressure" parameter.
Oxygen sensor (14) and oxygen buffer (15) - If the engine uses oxygen feedback in order to control the air/fuel ratio, the oxygen sensor and the oxygen buffer generate a signal that is proportional to the percent of oxygen in the exhaust manifold. The control system uses the signal to adjust the air/fuel ratio in order to achieve the level of emissions that is desired. To observe the output value of the sensor, use Cat ET to view the "Actual Oxygen" parameter.