Siemens PCS 7 Manual De Usuario

Introduction

 

MPC Level 

V 1.0, Beitrags-ID: 42200753 

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The control loop shows integrating behaviour if the position of mechanical parts is 

controlled and the speed of the actuator is available as manipulated variable. An 

"equilibrium condition" without move in the position only exists for a speed equal to 

zero. The valve actuator is a common example for position control in process 

plants. However, the valve position controllers are mostly integrated in the corre-

sponding actuators and hence not an issue for the DCS. 
 

The level of most chemical reactors has to be kept in certain limits during continu-

ous operation. Therefore the drain flow (rotational speed of pump or set point of 

subordinated flow controller) is available as manipulated variable and results in an 

integral part transfer function as described in section 2.3.1. A multivariable control 

problem including integral part transfer functions results if an additional quality con-

trol exists at the same reactor, e.g. with the reactor pressure as manipulated vari-

able (set point for the slave pressure controller). The residence time of the fluid in 

the reactor as well as the progress and the result of the reaction (the product qual-

ity) are dependant on the drain flow, which is the manipulated variable of the level 

controller.