Skip to Content

Register Login

Industry Online Support

Technical Forum

Navigation

How can I perform PID cascade?

Created by: OnoMas at: 12/5/2012 3:33 PM (4 Replies)

Rating (0)

Thanks 0

5 Entries

12/5/2012 3:33 PM	Rate (0)
OnoMas Posts: 43 Rating: (0)	FreakOnALeash, How can I perform PID cascade in s7 1200. I need to make 3 elemen PID control for boiler. As I check all input nodes, no available for cascading the PID. Attachment ThreeElementDrumLevelControl.jpg (636 Downloads)
OnoMas Posts: 43 Rating: (0)	Last edited by: OnoMas at: 12/6/2012 11:45 PM Last edited by: O_Moderator at: 12/6/2012 11:41 AM new subject after splitting from /tf/WW/en/Posts/80290#top
Suggestion To thank Quote Answer

12/6/2012 10:21 AM	Rate (0)
FreakOnALeash Posts: 267 Rating: (24)	Do you mean with "3 elemen PID control" the technology object "PID_3step"? http://support.automation.siemens.com/WW/view/en/62154322 The idea of a cascade is to use the PID output of the outer control loop as setpointfor the internal. So you need two PID technology objects and the internal must be called ina faster cycle interrupt. Sorry, but I don't understand the picture. What does the letters and numbers stand for? And what do you mean with "As O check..."?
FreakOnALeash Posts: 267 Rating: (24)
Suggestion To thank Quote Answer

12/6/2012 1:26 PM	Rate (0)
koenb Silver Member Joined: 6/26/2009 Last visit: 10/23/2024 Posts: 122 Rating: (23)	Hi , PID 3step is not the right solution for this kind of application. For your boiler feed control you may use two PID compact blocks. In relation to the steam consumption you have the related water input to the boiler . steam out = water in + blowoff . This is flow 1 first is a level PID wich you may scale into a flow component (m³/h) , flow2 Add both flow components together as the setpoint for a second PID ( flow ) to control your pump or feedvalve. This way , your feedsystem will react as soon as consumtion increases and not after the level drops below setpoint. koenb

Suggestion To thank Quote Answer

12/6/2012 11:42 PM	Rate (0)
OnoMas Posts: 43 Rating: (0)	@ koenb, Thank you for your explanation. I will try to apply this first. We know that boiler is very crucial proces so we have to be careful to design the block. one thing for the rest that I just able implement it in simulation only. Is it enough if we just simulate it in PLCcim?. Had you made it before?
OnoMas Posts: 43 Rating: (0)
Suggestion To thank Quote Answer

12/7/2012 9:10 AM	Rate (0)
koenb Silver Member Joined: 6/26/2009 Last visit: 10/23/2024 Posts: 122 Rating: (23)	Hi OnoMas, You are right , boiler levelcontrol is very crucial. When I wrote add the two components together , in fact i used a ratio in between. You can start with 75% signal from the classic levelcontrol and add 25% from the steamflow component. How much the ratiovalues must be depends from the steamconsumption , peaks or steady load. I have done it with a 1214 . ( keep in mind that still other things affect the level in the boiler . Cold or hot feedwater , conductivity , swell , probe location...) Give it a try and observe how it changes from classic control to consumption related. koenb
	Last edited by: koenb at: 12/7/2012 7:54 PM
Suggestion To thank Quote Answer

|

Share this page:

Share this page on...

Follow us on