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Smith-predictor for processes with long delay time

Created by: hdhosseini at: 6/10/2011 10:41 PM (3 Replies)

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6/10/2011 10:41 PM	Rate (0)
hdhosseini Diamond Member Joined: 1/28/2009 Last visit: 1/17/2025 Posts: 6858 Rating: (1366)	Smith Predictor for Control of Processes with Dead Times Some processes respond with high dead time.Dead time is one of the natural properties of a process.Consider the temperature of liquid in a tank should be regulated by steam(control valve on steam).When you open the control valve (Step change to process) more steam flows into the exchanger, conduction and convection are necessary to increase the value read by temperature transmitter. A normal PI controller must be tuned very sluggish for processes with large dead times and the control performance will decrease accordingly. The control performance can be considerably improved with the help of a so-called Smith-Predictor. Here is a configuration and also a simulation with different parameters: http://csd.newcastle.edu.au/simulations/roll_sim2.html From 07/2009 the function provided in advanced process control of PCS 7 V7.1. Following topics covered here: 1-Basic Principles of the Smith-Predictor 2-Implementation of the Smith-Predictor 3-Identification of the Process Model from Learning Data 4-Parameterization and Commissioning 5-Simulation Example 6-The Smith-Predictor in the Operation Phase Hope to helps hdhosseini
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6/11/2011 1:13 AM	Rate (0)
Krish Silver Member Joined: 5/24/2007 Last visit: 4/24/2024 Posts: 284 Rating: (27)	Thanks hdh, But this is more a theoretical controller. Most customers are happy to have a simple controller. But the reality is that most controllers are run in manual mode. A fraction of them are actually tuned.So end of the day..theoretical things are too far from shop floor.. Krish

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6/11/2011 2:26 AM	Rate (0)
hdhosseini Diamond Member Joined: 1/28/2009 Last visit: 1/17/2025 Posts: 6858 Rating: (1366)	Krish Thanks hdh, But this is more a theoretical controller. Most customers are happy to have a simple controller. But the reality is that most controllers are run in manual mode. A fraction of them are actually tuned.So end of the day..theoretical things are too far from shop floor.. Yes I know the point.When we think of a control loop, the idea is an ideal set of subsystem interconnected together and make a whole.Instrument and mechanical deficiency paralyze the loop. The goal and the ideal of a control engineer is to design the loop in ideal form and consider some constrains (limiting points).In real world, operators and maintenance team are available to take care of the system and rectify the deficiencies. Every function or product we are using, have deep theorical background which is hidden from the user.I recommend reading section 1-1 of the following book, when the author describes the terms such as quality of control and process optimization and ... . As you may read this manual , conventional PI controller can be used but what about control performance? A normal PI controller must be tuned very sluggish for processes with large dead times and the control performance will decrease accordingly. The control performance can be considerably improved with the help of a so-called Smith-Predictor. regards
	Last edited by: hdhosseini at: 6/11/2011 2:29 AM Demo Channel on Youtube
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This contribution was helpful to 2 thankful Users dchartier H-H

6/16/2012 12:14 AM	Rate (0)
metwally mustafa Silver Member Joined: 10/10/2010 Last visit: 12/5/2024 Posts: 307 Rating: (15)	thank you for this great advise i know that theoritical background is very important for control engineer despite the degree of difficulty with engineering control theory

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