Exam Question

(a) The block diagram shows the general arrangement. An Electronic governor provides engine speed adjustment from no-load condition to full load. It consists of a Controller, an Electro-Magnetic Pickup (MPU) and an actuator to carry out the necessary speed control and regulation. The speed sensor consists of a set of gear teeth that rotate at engine speed and a Magnetic Pick Up (MPU) that has a slight air gap. The MPU has a permanent magnet with a pole piece surrounded by a coil, the MPU is installed above the flywheel teeth and depending upon its distance from the gear teeth or slot, the magnetic field of the MPU varies from a maximum to a minimum respectively. The permanent magnet creates its own magnetic field. During running as each ferrous gear tooth passes the core, the reluctance path is decreased and the flux lines increase. The change in flux lines produces an ac sine wave voltage in the coil the frequency of which represents the engine speed.
The AC voltage is amplified and rectified to a DC voltage which is proportional to the engine RPM. This DC voltage is compared with the desired set voltage at the controller (corresponding to the desired RPM) and an appropriate electric signal is sent to an electro-hydraulic converter. The electro-hydraulic converter processes the signal and operates an actuator (hydraulic cylinder and piston) to increase or reduce the fuel supply as required. An actuator position feedback to the controller is provided as shown.
The electronic controller has different modes of operation to implement various functions. These include;
Detecting the starting of an engine and subsequently directing the fuel supply.