Servo-control-drive reliability

The primary coolant system flow control scheme is shown in Figure C-61. Flow control will be accomplished through adjustments to the speed of the primary pump drive turbines. Discharge flow rates from each of the five primary ptmps will be monitored and a constant pressure differential across each flow monitor will be maintained by adjustments to each individual turbine speed control. A total flow controller will be utilized to control the sum of the five cells flow, i.e., total flow, by re-adjueting the five Individual turbine speed controllers. Primary coolant flow control is a vitally important system and steps were taken to enhance systetii reliability and minimize the importance of component failure. Liberal use was made of summing point monitors, servo followers, and selector stations to accomplish these objectives. 

Frequently, an interface application will require that the PC controls the motion of an object. A device that Is often used to power or move a shaft in precise Increments, directions and speeds Is a stepper motor. Here we consider two approaches to this problem. The first uses the stepper motor, a device whose angle of rotation is known reliably from the pulses which have been sent to it. Once calibrated and Initialized, no feedback of the rotor s position is necessary, unless the speed demanded is too high or the torque required Is too great. Running a motor this way without feedback is called OPEN LOOP. The second method uses feedback, is a CLOSED LOOP approach, and Is called a servo system. The servo system can respond more quickly and accurately than the open-loop stepper motor system and Is relatively insensitive to hardware variations. However, It requires position sensors as well as more complicated drive electronics to ensure stability. 

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