Process ControlsCONTROLLERSCONTROLLERSMechanical "watchdogs" called controllers are installed in a system to maintainprocess variables within a given parameter.EO 1.5 STATE the purpose of the following components of atypical control station:a. Setpoint indicatorb. Setpoint adjustmentc. Deviation indicatord. Output metere. Manual-automatic transfer switchf. Manual output adjust knobEO 1.6 DESCRIBE the operation of a self-balancing controlstation.ControllersControllers are the controlling element of a control loop. Their function is to maintain a processvariable (pressure, temperature, level, etc.) at some desired value. This value may or may notbe constant.The function is accomplished by comparing a setpoint signal (desired value) with the actual value(controlled variable). If the two values differ, an error signal is produced.The error signal is amplified (increased in strength) to produce a controller output signal. Theoutput signal is sent to a final control element which alters a manipulated variable and returnsthe controlled variable to setpoint.This chapter will describe two controllers commonly found in nuclear facility control rooms.Although plants may have other types of controllers, information presented here will generallyapply to those controllers as well.ControlStationsControl stations perform the function of a controller and provide additional controls andindicators to allow an operator to manually adjust the controller output to the final controlelement.Figure 32 shows the front panel of a typical control station. It contains several indicators andcontrols. Each will be discussed.Rev. 0 Page 47 IC-07
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