McClure and Hove 



of the operating mode. If the system is operated in the automatic mode, orders 

 are derived from the positioning computer. If the manual mode is in use, pro- 

 pulsion unit orders are manually introduced. 



Positioning unit azimuth orders are routed to the Port Pos. Unit Azimuth 

 Indicator-Control and the Stbd. Pos. Unit Azimuth Indicator -Control, on the po- 

 sitioning control console, where this information is displayed and compared to 

 actual positioning unit azimuth. If a discrepancy exists, signals are sent to the 

 port and starboard Pos. Unit Azimuth Drive motor controllers which drive the 

 positioning units to the desired azimuth. Signals from Pos. Unit Azimuth Syn- 

 chros geared to the units are used to insure that ordered and actual azimuth an- 

 gles are the same. 



Positioning unit thrust rpm orders are sent to port and starboard Pos. Unit 

 Thrust Indicator -Control modules where they are compared to the actual posi- 

 tioning unit propeller shaft rpm. If a discrepancy exists, signals are sent to 

 port and starboard Pos. Unit Gen. Field Control modules in the engine room. 

 These modules control appropriate generator fields which in turn control the 

 speed of the Pos. Unit Drive Motors. Port and Starboard Pos. Unit Tachometers 

 generate shaft rpm signals for comparison to rpm orders. 



Main propulsion motor thrust orders are routed in a manner similar to the 

 positioning unit thrust orders. In this case, functions travel to Main Propulsion 

 Indicator-Control modules, Main Prop. Gen. Field Control modules and Main 

 Propulsion Motors, Main Shaft Tachometers generate signals which are used 

 for ordered and actual shaft rpm comparison. 



Alarms associated with each indicator-control module indicate when a sus- 

 tained discrepancy exists between actual and ordered quantities. 



Based on component tolerances, error analysis of the computer circuits in- 

 dicates an error of about 20 ft when the platform is over the hole. Because of 

 simplifying assumptions in the mathematical model, this error increases to ap- 

 proximately 40 ft at the maximum allowable distance off. 



446 



