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| Illustration 1 | g00866096 |
The speed switch is typically in a control panel or a terminal box. | |
The speed switch receives a signal from a speed sensor that senses the rotation of the flywheel ring gear's teeth. The speed switch uses the signal to interpret the engine rpm. The speed switch has contacts for the following parameters:
- Crank terminate
- Engine's oil step speed
- Engine overspeed
- Nine second delay timer after crank termination
The operation of the speed switch is described below.
Crank terminate - When the engine is stopped, terminal 12 is normally closed with the common terminal 11. The contact opens upon start-up after the engine speed reaches 165 rpm and the common terminal 11 closes with the normally open terminal 10. This is the contact for the crank terminate relay. The contact remains closed during engine operation. The contact opens upon shutdown after the engine rpm is 0 for two seconds.
Engine's oil step speed - Before the engine reaches 75 percent of the rated speed, terminal 15 is normally closed with the common terminal 14. At nine seconds after the engine speed reaches 75 percent of the rated speed, the common terminal 14 closes with the normally open terminal 13. Closure of the contact for terminal 13 enables the contactor for low engine oil pressure at high engine speed. The contact for terminal 13 remains closed until the engine speed is reduced to less than 75 percent of the rated speed.
Engine overspeed - During normal operation, terminal 9 is normally closed with the common terminal 8. If the engine speed reaches 113 percent of the rated speed, the common terminal 8 closes with the normally open terminal 7. Closure of this contact generates a shutdown for engine overspeed. The red "OVERSPEED" indicator is illuminated. Terminals 7 and 8 remain closed until the engine speed is reduced to less than 113 percent of the rated speed and the "RESET" button is pressed. The red "OVERSPEED" indicator is also extinguished. The "RESET" must be pressed before the engine can be restarted.
Delay timer - Steps 1 through 3 describe the operation of the delay timer. The steps are repeated for each engine shutdown and start-up.
- When the engine is stopped for at least two seconds, the crank terminate relay is OFF and the "TD" terminal 1 is powered. The immediate energizing of terminal 1 causes the normally open terminal 16 to close with the common terminal 17.
- When the engine is started, activation of the crank terminate relay removes power from terminal 1. This starts the nine second delay.
Although power is removed from terminal 1, the "TD" relay remains energized.
- After the nine seconds have expired, power is removed from the "TD" relay. This closes the common terminal 17 with the normally closed terminal 18.
Closure of terminals 17 and 18 enable the contactor for low engine oil pressure at low engine speed. This contactor remains enabled until the engine is stopped for at least two seconds.