You are not registered yet. Please click here to register!


 
 
plc storereviewsdownloads
This board is for PLC Related Q&A ONLY. Please DON'T use it for advertising, etc.
 
Try our online PLC Simulator- FREE.  Click here now to try it.

---------->>>>>Get FREE PLC Programming Tips

New Here? Please read this important info!!!


Go Back   PLCS.net - Interactive Q & A > PLCS.net - Interactive Q & A > LIVE PLC Questions And Answers

PLC training tools sale

Reply
 
Thread Tools Display Modes
Old August 2nd, 2018, 10:27 PM   #1
Cookz615
Member
United States

Cookz615 is offline
 
Cookz615's Avatar
 
Join Date: Feb 2017
Location: tennessee
Posts: 12
Allen Bradley 5000 P.I.D. Setup

Hello everybody,

It's been a good while, hope everyone is doing well!

I've recently been task to setup a P.I.D. to control the water level in our sludge collection hoppers. I am using an Einfield S2-025-U-04 proportional control valve with an SMC cylinder and a SICK linear transducer for positional feedback of the cylinder to the Einfield valve.

I have a P.I.D. setup and controlling somewhat but cant seem to figure out how to completely take out the pulsation of the water level due to the output of the P.I.D. constantly updating and changing the output.

This is the first time I have ever touched a P.I.D. "As you can probably tell" so I don't know if this can be tuned out in the P.I.D. instruction completely or if I need to write logic to open up the acceptable window for level and only allow the P.I.D. to run when its outside that window.

Ideally I would like to keep the water level at around 15 in. I believe I could stand to do a plus or minus 1 in using compare statements to enable or disable the P.I.D. Not sure the best course to take.

Any help would be greatly appreciated.

Thanks,
  Reply With Quote
Old August 3rd, 2018, 04:01 AM   #2
rdrast
Lifetime Supporting Member
United States

rdrast is offline
 
rdrast's Avatar
 
Join Date: Apr 2003
Location: South Carolina Lowcountry
Posts: 5,251
Enabling/Disabling the PID is not the solution. You probably just need to actually tune it better.



Check here for the Zeigler-Nichols approach, which is fairly simple to do (you can create a trend in Logix to determine the time constant of your process).
__________________
------------------------------------
How to ask questions the SMART Way!

Look First, Ask Second!

  Reply With Quote
Old August 3rd, 2018, 08:04 AM   #3
Mispeld
Member
United States

Mispeld is offline
 
Mispeld's Avatar
 
Join Date: Feb 2017
Location: VA
Posts: 345
Is it possible for you to post an image of a trend charts showing the controller output percent and level measurement? Ideally, this would be during a time when the process is somewhat stable (i.e., water input to the hopper is steady), and you have the PID in manual mode at a fixed percent output. Then change ("bump") the controller output in manual by an amount that changes the level, but still within your acceptable safety tolerance. Stop the trend chart after it appears the level has reached a new equilibrium.

This request assumes a couple things: that your water/sludge input is fairly stable over the response time of the valve, your output flow is reasonably linear in the control range (valve percent) where you normally operate, and that level measurement is responsive and repeatable. With a correctly configured PID loop, this type of trend can be used for ballpark tuning, or to identify problems where tuning might not be root cause of observed issues.
__________________
"The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge." -Stephen Hawking
  Reply With Quote
Old August 9th, 2018, 05:44 AM   #4
Cookz615
Member
United States

Cookz615 is offline
 
Cookz615's Avatar
 
Join Date: Feb 2017
Location: tennessee
Posts: 12
Excellent! Thank you!
  Reply With Quote
Old August 9th, 2018, 11:16 AM   #5
Peter Nachtwey
Member
United States

Peter Nachtwey is offline
 
Peter Nachtwey's Avatar
 
Join Date: Apr 2002
Location: Vancouver, WA, US
Posts: 6,718
Ditto the suggestion about getting a trend.

Quote:
Check here for the Zeigler-Nichols approach, which is fairly simple to do (you can create a trend in Logix to determine the time constant of your process).
NO, NO, NO, NO!!!! NEVER!!! Z-N keeps control techniques in the dark ages and isn't applicable to many system like tank level control

You should always state whether the valve controls the inflow or outflow. It makes a different.
I am assuming the valve controls the outflow.
I am assuming maximum valve outflow matches the max inflow

Why use a PID? Keep it simple.
Just use proportional band control where the valve is closed at 14 inches and open 100% at 16 inches. At 14.5 inches the valve is open 25% and at 15 inches the valve is open

Most proportional valves do not control flow proportional to the control signal. Many proportional valve are non-linear or have a huge dead band so it may take 20% control signal to get any flow. This too should be stated or a link to the valve specs should be provided.
__________________
"Living is easy with eyes closed, misunderstanding all you see...." Strawberry Fields Forever, John Lennon
  Reply With Quote
Old August 9th, 2018, 01:05 PM   #6
raffles
Member
Canada

raffles is offline
 
Join Date: Dec 2013
Location: Vernon, BC
Posts: 74
Quote:
Originally Posted by Peter Nachtwey View Post
NO, NO, NO, NO!!!! NEVER!!! Z-N keeps control techniques in the dark ages and isn't applicable to many system like tank level control
Not wanting to hijack the thread to much but I'm a big opponent of ZN as well. The fact that you are willingly pushing a process to the point of instability is just bonkers in the real world
  Reply With Quote
Old August 10th, 2018, 03:27 AM   #7
rdrast
Lifetime Supporting Member
United States

rdrast is offline
 
rdrast's Avatar
 
Join Date: Apr 2003
Location: South Carolina Lowcountry
Posts: 5,251
I only mentioned ZN, as it is a very basic, and simple method of at least getting something under control. It seems a lot of people just drop in a PID(E) instruction and expect it to work by randomly popping in numbers.


Almost every write up of ZN at least goes through the basics of figuring out the time constants of your system.
__________________
------------------------------------
How to ask questions the SMART Way!

Look First, Ask Second!

  Reply With Quote
Reply
Jump to Live PLC Question and Answer Forum

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Topics
Thread Thread Starter Forum Replies Last Post
Logix 5000 install problem smiller LIVE PLC Questions And Answers 16 May 26th, 2015 09:47 PM
Help! DeviceNet for SLC500 Allen Bradley Buscom LIVE PLC Questions And Answers 7 October 7th, 2013 07:33 AM
Message Setup? Allen Bradley Contol Logix pater01 LIVE PLC Questions And Answers 37 September 24th, 2012 02:39 AM
Learning Allen Bradley mbferrari LIVE PLC Questions And Answers 9 March 11th, 2009 12:25 PM
RSLogix 5000 V15 Features Samneggs LIVE PLC Questions And Answers 18 April 20th, 2006 05:45 PM


All times are GMT -5. The time now is 09:15 PM.


.