Due to their reliability and long life, proximity sensors are in wide use in industrial applications. In essence, they are non-mechanical switches with no moving parts.  Proximity sensors require no physical contact for activation and have less critical clearance requirements than the traditional magnetic pickups.  The sensors work in tandem with metal targets.  When a target moves into the proximity sensor’s pickup field, the sensor generates an electronic speed  or direction signal.

 

The EMI Digital Shaft Tachometer system uses two proximity sensors - one in the measurement of shaft rotation speed, the second in determining rotation direction.  The proximity sensors are stationary but the targets rotate with the propeller shaft and pass into the sensors’ pickup fields once each revolution.

 

The Shaft Tachometer Meter Module can be installed in up to 6 locations on the ship.  Its digital circuitry receives the output from the proximity sensors, interprets the signals and displays both direction and speed.  An RS-485 Communications Port is available to allow for direct interface to shipboard networks. EMI facilitates the installation of the Shaft Tachometer System by providing a junction box which is pre-wired to the proximity sensors.  The proximity sensors are  mounted on a bracket which is attached to an adjustable mounting plate.

 

The Engine Room Shaft Tach interface panel provides a connection point for the two sets of proximity pick-ups mounted on the Port and Starboard main engine propeller shafts. Circuitry within the interface panel converts the pulses from the pick-ups to an analog voltage signal.  The port and starboard voltage signals generated by each panel are used to drive multiple shaft tach meters located throughout the vessel.

 

The Engine Room Shaft Tach Control Panel has two meters mounted in the door of the enclosure which display Port and Starboard main engine RPMs.  Each shaft tach meter has a range of 0-500 RPM in the astern and ahead directions.