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explain the reasons for power control using ion chambers at low
power and in-core detectors at high power;
Control
• identify the controlled and manipulated variables;
• sketch a simple block diagram and indicate set point,
measurement, error, output and disturbances;
• state the difference between open and closed loop control;
• state the basic differences between feedback and feed forward
control;
• explain the general on/off control operation;
• explain why a process under on/off control is not controllable at
the set point;
• explain why on/off control is suitable for slow responding
processes;
• explain the meaning of proportional control in terms of the
relationship between the error signal and the control signal;
• explain why offset will occur in a control system, with
proportional control only;
• choose the controller action for corrective control;
• convert values of PB in percentage to gain values and vice-versa;
• determine the relative magnitude of offset with respect to the
proportional band setting;
• state the accepted system response, i.e., ¼ decay curve, following a
disturbance;
• explain the reason for the use of reset (integral) control and its
units;
• sketch the open loop response curve for proportional plus reset
control in response to a step disturbance;
• state two general disadvantages of reset control with respect to
overall loop stability and loop response if the control setting is
incorrectly adjusted;
• calculate the reset action in MPR or RPM given a control system’s
parameters;
• state, the purpose of rate or derivative control;
• state the units of derivative control;
• justify the use of rate control on slow responding processes such
as heat exchangers;
• explain why rate control is not used on fast responding
processes.
• sketch the open loop response curve for a control system with
proportional plus derivative control modes;
• state which combinations of the control modes will most likely
be found in typical control schemes;
Note
Science and Reactor Fundamentals – Instrumentation & Control 6
CNSC Technical Training Group
Revision 1