ELBOW 6V9208 - Caterpillar

Electric Protective System
Introduction
The electric protective system is designed to activate an alarm or shut the engine off if there is a problem or a failure in any of four different engine systems. The engine systems monitored are: engine overspeed, starter motor crank terminate, engine oil pressure and engine coolant temperature.The electric protective system consists of the basic components that follow: magnetic pickup, electronic speed switch, water temperature contactor switch, two time delay relays and two slave relays. This system monitors the engine from starting through rated speed.Component Description
Magnetic Pickup (MPU) - The magnetic pickup is a single pole, permanent magnet generator made of wire coils around a permanent magnet pole piece. As the teeth of the flywheel ring gear go through the magnetic lines of force around the pickup, an AC voltage is made. A positive voltage is made when each tooth goes by the pole piece. Each time the space between the teeth goes by the pole piece, a negative voltage is made. Engine speed is then determined by the frequency of these signals. Electronic Speed Switch (ESS) - The 4W2218 Electronic Speed Switch can easily be identified by its black color (the earlier speed switch was yellow). This speed switch has controls (in a single unit) to monitor three of the basic functions. These three functions are: Engine Overspeed - An adjustable engine speed setting (normally 118% of rated speed) that gives protection to the engine from damage if the engine runs too fast. This condition will cause a switch to close that shuts off both the inlet air and the fuel to the engine. Crank Terminate (Starter Motors) - An adjustable engine speed setting that gives protection to the starter motor from damage by overspeed. This condition will cause a switch to open that stops current flow to starter motor circuit, and the starter motor pinion gear will then disengage from engine flywheel ring gear. Engine Step Oil Pressure - An adjustable engine speed setting that gives protection to the engine from a failure caused by not enough oil pressure. To maintain desired protection through the complete speed range of engine operation, two different oil pressure switches are used [280 kPa (40 psi), 140 kPa (20 psi)]. Once the step oil pressure speed setting is made, an engine that runs above this speed setting must maintain an oil pressure that is more than 280 kPa (40 psi). An engine that runs at a speed below this speed setting must maintain an oil pressure that is more than 140 kPa (20 psi). If either condition is not correct, a switch will close to activate an alarm or cause the fuel to be shut off to the engine. Water Temperature Contactor Switch - This contactor switch is a separate unit (mounted in the regulator housing) that is wired into the shutdown circuit. It has an element that feels the temperature of the coolant (it must be in contact with the coolant). When the engine coolant temperature