Siemens Time Clock pcs 7 User Manual

Introduction 
 

 

10 

MPC Level 

V 1.0, Beitrags-ID: 42200753 

 

C

opyr

ight 



 Si

em

ens

 AG 2

010

 Al

l r

ights r

es

er

ved 

feed water tanks. There are different objectives for level control according to the 

plant context [also see Related Literature /2./]: 


  Keep level constant (exactly at the set point) – important for levels directly in-

fluencing the process; disturbances are passed through to the output (drain). 



  Keep level as small as possible – if “dead volume” and inventory are undesir-

able. 



  Keep level inside specified limits while using the tank as buffer – changes in 

level are tolerated to achieve a smooth drain flow. 

 

Figure 2-3 Examples of level control (marked in red) in a typical part of plant (distillation 

column) [also see Related Literature /1./]. 

 

 

In some cases the pressure control in tanks behaves in a similar way as the level 

control. The control loop shows an integral behaviour, if the manipulated variable is 

a gas feed (e.g. admission of inerts) and no pressure loss to the environment ex-

ists. Typically a separate purge valve exists in such cases to discharge gases. The 

pressure controller uses a split range function to access either the feed valve or the 

purge valve.