Top Control

OPEN PARA LA SEGURIDAD Y EL RENDIMIENTO

Mejore la seguridad y el rendimiento de su planta gracias a la gestión de alarmas, la supervisión de rendimiento y de activos, la visualización web de datos, la optimización, el control avanzado y la sintonía con la nueva herramienta TaiJi.

Repiensen sus métodos de trabajo y obtengan resultados inmediatos gracias a nuestros servicios, nuestra capacitación y nuestra pericia en asesoría. Manejen el cambio inteligentemente con nuestras soluciones probadas.

Asociado certificado

October 2004

In this issue

	About us
	Classes and seminars
	Trick for this month
	To contact us

See our previous issues :
http://www.topcontrol.com/techinfo/news.php

About us

ISA Expo 2004

Thank you for visiting us at the show…

Classes & seminars

See our calendar for 2004 Classes & Seminars

See at http://www.topcontrol.com/training/tcalendar.php

Moncton, New-Brunswick, Canada, October 27-28-29
VA-900-3, Control valve selection
http://www.topcontrol.com/training/tlistcourses.php?idcours=13

Las Vegas, Nevada, November 2-3-4
SE-100-3 - Seminar on modern control methods
http://www.topcontrol.com/training/tlistcourses.php?idcours=6

Seattle, Washington, November 17-18-19
EX-501-3 - Detailed Loop Analysis with ExperTune
http://www.topcontrol.com/training/tlistcourses.php?idcours=10

Rotterdam, Netherlands, November 24-25-26
EX-501-3 - Detailed Loop Analysis with ExperTune
http://www.topcontrol.com/training/tlistcourses.php?idcours=10

Clearwater Beach, Florida, November 30-December 1-2
EX-501-3 - Detailed Loop Analysis with ExperTune
http://www.topcontrol.com/training/tlistcourses.php?idcours=10

Trick for this month: Estimating dead time to validate tuning parameters!

Knowing roughly the dead time will enable one to validate PID tuning parameters.

Indeed,

If the controller algorithm is serial or ideal,
If the controller has been tuned to reject a disturbance,
- Then, t_s<T_F<T_D<t_d<T_I<t_settling,
Or,
- t_s is scan time, ~1/10 t_d
- T_F is PV filter time constant (transmitter or controller), ~1/5 t_d
- T_D is derivative time, ~½ t_d
- t_d is dead time,
- T_I is integral time, ~3 t_d
- t_settling is settling time after a disturbance, ~10 t_d.

After a change in controller output (manual or auto), dead time is the period of time needed before the PV (measurement) starts to react.

For example, in a control loop where an additive is added to main flow, the dead time corresponds to the time needed for the additive to reach the sensor (perfect mixing).

Since the velocity in pipes is usually 5 to 10 ft/s, the dead time is easily estimated using the distance. For example, in a consistency loop where the transmitter is located 15 ft after the pump (used for mixing) the dead time is ~ 3s (using 5 ft/s to be conservative).

Each device (P/I, I/P, transmitter, positionner, actuator, …) has its own response time and will increase dead time. A simple rule of thumb is to use 0.5s for each.

Thermowells, gas probes, pH electrodes, … have long response time varying with operating conditions.

Using an approximate estimate will let you determine if tuning parameters make sense.

To contact us

Comments, suggestions and requests are welcomed. Please e-mail us at: info@topcontrol.com

You are welcomed to visit our web site :http://www.topcontrol.com

	49 Bel-Air Street, Lévis, QC G6V 6K9, Canada Phone: (418) 834-2242 Fax: (418) 834-2651
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