Using Wireless Measurements
in Control Applications

Standards

Terry Blevins
Mark Nixon
Marty Zielinski

Certification
Ed...
Presenters

Marty Zielinski
Terry Blevins

Copyright 2013 ISA. All Rights Reserved. www.isa.org
Presented at ISA Automatio...
Agenda

•
•
•
•
•

Wireless Impact on Control
Modified PID, PIDPlus, for Wireless Measurements
Performance Comparison to W...
Challenge – Control Using Wireless
• It is desirable to minimize how often a measurement value is
communicated to reduce t...
Conventional Approach –
Over Sampling of Measurement

Copyright 2013 ISA. All Rights Reserved. www.isa.org
Presented at IS...
Wireless Communication
Two communication techniques best fit control applications and
minimize the power consumption by th...
Conventional PID - Impact of Wireless
• The underlying assumption in traditional control design is that the
PID is execute...
PIDPlus for Wireless Communications
Automatic compensation for setpoint change, measurement update rate.
No need to modify...
PIDPlus Using Wireless Transmitter vs.
Conventional PID and Wired Transmitter
Lambda Tuning ʎ = 1.0
Communication Resoluti...
CONTROL PERFORMANCE DIFFERENCE

• Window communications reduce the number of transmissions
by over 96 %.
• The impact of n...
PID Performance for Lost Communications
• The Conventional PID provides poor dynamic
response when wireless communications...
Wireless Communication Loss –
During Setpoint Change

Setpoint

PIDPlus
Control
Measurement
PID
PIDPlus

Control Output
PI...
Field Trail Site University of Texas at Austin
• The Separations Research
Program was established at
the J.J. Pickle Resea...
Steam Flow To Stripper Heater

Copyright 2013 ISA. All Rights Reserved. www.isa.org
Presented at ISA Automation Week 2013
...
Column Pressure Control

Copyright 2013 ISA. All Rights Reserved. www.isa.org
Presented at ISA Automation Week 2013
Nashvi...
PC215 On-line Column Pressure Control
Wired Measurement
Used in Control

Wireless Measurement
Used in Control

Copyright 2...
Control Performance – Wired vs Wireless
•

•

Copyright 2013 ISA. All Rights Reserved. www.isa.org
Presented at ISA Automa...
Summary

• Wireless measurements may be used in closed loop
control applications.
– Window communications minimize power c...
References
•
•
•
•
•

•

•

•

K.J. Åstrӧm, and T. Hägglund, in Advanced PID Control, ISA, 2006., pp. 85-86
K.J. Åstrӧm. “...
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Using Wireless Measurements in Control Applications

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Source: International Society of Automation (ISA) Copyright © 2013. Reprinted by permission. All rights reserved.

Presented at ISA Automation Week by Emerson Process Management's Terry Blevins, Mark Nixon, and Marty Zielinski

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Using Wireless Measurements in Control Applications

  1. 1. Using Wireless Measurements in Control Applications Standards Terry Blevins Mark Nixon Marty Zielinski Certification Education & Training Publishing Conferences & Exhibits Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  2. 2. Presenters Marty Zielinski Terry Blevins Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013 2
  3. 3. Agenda • • • • • Wireless Impact on Control Modified PID, PIDPlus, for Wireless Measurements Performance Comparison to Wired Transmitter Test results – Field Installations Conclusion Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  4. 4. Challenge – Control Using Wireless • It is desirable to minimize how often a measurement value is communicated to reduce transmitter power consumption,. • Most multi-loop controller in use today are designed to oversample the measurement by a factor of 2-10X to avoid the restrictions of synchronizing the measurement value with the control, • Also, to minimize control variation, the typical rule of thumb is that feedback control should be executed 4X to 10X times faster that the process response time, process time constant plus process delay. • The conventional PID design (based on difference equation, z-transform) assumes that a new measurement value is available each execution and that control is executed on a periodic basis. Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  5. 5. Conventional Approach – Over Sampling of Measurement Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  6. 6. Wireless Communication Two communication techniques best fit control applications and minimize the power consumption by the wireless device transmitting the measurement value. • Continuous – The device wakes up at a configured update period, senses the measurement and then communicates the value. • Window – The device wakes up at a configured update period, senses the measurement and then communicates the measurement if the specified trigger value is exceeded. Window communications is the preferred method since for the same update period less power is required. Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013 6
  7. 7. Conventional PID - Impact of Wireless • The underlying assumption in traditional control design is that the PID is executed on a periodic basis. • When the measurement is not updated on a periodic basis, then the calculated reset action may not be appropriate. • If control is only executed when a new measurement is communicated, then this could delay control response to setpoint changes and feedforward action on measured disturbances. Conventional PID Design Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  8. 8. PIDPlus for Wireless Communications Automatic compensation for setpoint change, measurement update rate. No need to modify tuning as sample rate changes Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  9. 9. PIDPlus Using Wireless Transmitter vs. Conventional PID and Wired Transmitter Lambda Tuning ʎ = 1.0 Communication Resolution = 1% Communication Refresh = 10sec Setpoint PIDPlus Control Measurement PID PIDPlus Control Output PID Unmeasured Disturbance Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  10. 10. CONTROL PERFORMANCE DIFFERENCE • Window communications reduce the number of transmissions by over 96 %. • The impact of non-periodic measurement updates on control performance as measured by Integral of Absolute Error (IAE) is minimized through the use of the PIDPlus for wireless communication. Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  11. 11. PID Performance for Lost Communications • The Conventional PID provides poor dynamic response when wireless communications are lost. • The PIDPlus improves the dynamic response under these conditions Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  12. 12. Wireless Communication Loss – During Setpoint Change Setpoint PIDPlus Control Measurement PID PIDPlus Control Output PID Communication Loss Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  13. 13. Field Trail Site University of Texas at Austin • The Separations Research Program was established at the J.J. Pickle Research Campus in 1984 • This cooperative industry/university program performs fundamental research of interest to chemical, biotechnological, petroleum refining, gas processing, pharmaceutical, and food companies. • CO2 removal from stack gas is a focus project for which WirelessHART transmitters were installed for pressure and steam flow control Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  14. 14. Steam Flow To Stripper Heater Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  15. 15. Column Pressure Control Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  16. 16. PC215 On-line Column Pressure Control Wired Measurement Used in Control Wireless Measurement Used in Control Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013 • The same dynamic control response was observed for SP changes • Original plant PID tuning was used for both wired and wireless control GAIN=2.5 RESET=4 RATE=1
  17. 17. Control Performance – Wired vs Wireless • • Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013 Comparable control as measured by IAE was achieved using WirelessHART Measurements and PIDPlus vs. control with wired measurements and PID. The number of measurement samples with WirelessHART vs Wired transmitter was reduced by a factor of 10X for flow control and 6X for pressure control – accounting for differences in test duration.
  18. 18. Summary • Wireless measurements may be used in closed loop control applications. – Window communications minimize power consumption • The performance of PIDPlus in a wireless control network is comparable to PID with wired inputs – PIDPlus handles lost communications and recovery after loss of communications. • PIDPlus tuning depends only upon process dynamics, not on wireless update rate Copyright 2013 ISA. All Rights Reserved. www.isa.org Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013
  19. 19. References • • • • • • • • K.J. Åstrӧm, and T. Hägglund, in Advanced PID Control, ISA, 2006., pp. 85-86 K.J. Åstrӧm. “Event based control”, in Analysis and Design of Nonlinear Control Systems, Springer Verlag, 2007, pp.127-147 T. Blevins, and M. Nixon, in Control Loop Foundation – Batch and Continuous Processes, ISA. pp. 266, 270, 393 T. Blevins, (2012) “PID Advances in Industrial Control”, IFAC Conference on Advances in PID Control PID'12, 2012, http://pid12.ing.unibs.it/sp_blevins.html S. Han, X. Zhu, K.M. Aloysius, M. Nixon, T. Blevins, D. Chen, “Control over WirelessHART Network”, 36th Annual Conference of the IEEE Industrial Electronics Society, 2010, http:// www.cs.utexas.edu/~shan/paper/slides-iecon10.pptx F. G., Shinskey, “The Power of External Reset Feedback”, Control, ,May, 2006, pp.5363, http://classes.engineering.wustl.edu/2009/spring/che433/2009LAB/Experiment%206/external-reset.pdf F. Siebert, and T. Blevins, “WirelessHART Successfully Handles Control”, Chemical Process, January, 2011 http://www2.emersonprocess.com/siteadmincenter/PM%20Articles/WirelessHART%20S uccessfully%20Handles%20Control.pdf M. Rabi and K. H. Johansson. “Event-triggered strategies for industrial control over wireless networks”, In Proceedings of 4th Annual International Conference on Wireless Internet, Maui, Hawaii, USA, 2008. ISA. All Rights Reserved. www.isa.org Copyright 2013 Presented at ISA Automation Week 2013 Nashville, Tennessee •Renaissance Nashville, USA, 4-7 November 2013 19
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