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.

New Here? Please read this important info!!!

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

Thread Tools Display Modes
Old October 20th, 2015, 03:27 PM   #46
United States

kamenges is offline
kamenges's Avatar
Join Date: Nov 2002
Location: Brillion, WI
Posts: 4,309
I agree the PV looks like it may have taken a shot from a derivative at setpoint change. The thing that I find odd is that there is nothing in the CV that suggests that. It's like the PV and CV graphs are from two different processes.

Originally posted by Paully's5.0:

By understanding the rate of change, we can start to predict the future.
I've never been a big fan of the whole "predicts the future" thing when discussing derivatives. It makes the use of the derivative seem "magical" to people who are just trying to grasp it.

When I talk about the derivative in a PID to people new to it I generally refer to an automotive shock absorber (dampers to those outside the U.S.). The faster you try to move the thing you are concerned with the harder the derivative will fight to keep it still.

The problem with the derivative is when the feedback lies about the process velocity. This is where people start talking about the derivative causing all sorts of chatter and noise. It isn't specifically the derivative; it is the feedback.

  Reply With Quote
Old October 20th, 2015, 03:34 PM   #47
United Kingdom

Oceansoul is offline
Join Date: Apr 2010
Location: England
Posts: 308
I was reading an old manual at work earlier for Heenan Inverter drives and in there is this basic explanation of PID control. Not the most scientific, but i found it quite helpful.

  Reply With Quote
Old October 21st, 2015, 12:25 AM   #48
Peter Nachtwey
St Kitts and Nevis

Peter Nachtwey is offline
Peter Nachtwey's Avatar
Join Date: Apr 2002
Location: No income tax, no capital gains tax. Freedom!
Posts: 8,300
Originally Posted by kamenges View Post
I've never been a big fan of the whole "predicts the future" thing when discussing derivatives.
Me neither. The derivative term adds damping. The derivative gain can be used to place a pole. The derivative gain can also be used to extend bandwidth.
"Living is easy with eyes closed, misunderstanding all you see...." Strawberry Fields Forever, John Lennon
  Reply With Quote
Jump to Live PLC Question and Answer Forum

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
PID - A challenge, is a PID good enough? Peter Nachtwey LIVE PLC Questions And Answers 21 June 26th, 2019 06:14 AM
AB PLC5 PIDs Derek McFarland LIVE PLC Questions And Answers 23 March 2nd, 2005 03:18 AM
Use a PID? MarBa LIVE PLC Questions And Answers 4 May 8th, 2003 10:31 PM
how often should I trigger the PID? Ron Beaufort LIVE PLC Questions And Answers 11 February 22nd, 2003 12:57 PM
Cascading Sparky LIVE PLC Questions And Answers 24 February 17th, 2003 01:33 PM

All times are GMT -4. The time now is 08:09 AM.