Response Electronics CL6011B Especificaciones descargar pdf (Pagina 40)

3Ć20 Theory of Operation: Point Processing

Original Ć June 1990CE4.2:CL6211

3.3.3.1.1 Anti-Reset Windup

In a situation where a point has reached an output limit, and the integral

action has been stopped to prevent windup, it may be desirable to have

the IVP move very rapidly once it comes off of its limit. The Anti-Reset

Windup (ARW) feature provides the option of having the integral term of

a DCP unwind at a speed 16 times the normal, tuned reset speed. This

feature reduces the effects of reset windup on process variable

overshoot.

The PID PCA allows the user to establish limits based on the position of

the IVP that define when the ARW action occurs. The ARW High Limit

and ARW Low Limit values are used to determine the boundaries. When

the calculated IVP exceeds an ARW limit but not an output limit, the

integral action provides normal reset speed for windup" towards the

output limit and fast reset speed for wind down" back to the ARW limit.

IVP

Setpoint

+1/2 P.B.

- 1/2 P.B.

ARW Low Limit

IVP Low Limit

Figure 3Ć8. Anti-Reset Windup

In the example shown in Figure NO TAG, the IVP of the DCP has reached

a lower limit at Point A. When the magnitude of the error term decreases

to within 1/2 the proportional band at Point B, the IVP starts to come off

of the limit. As the process variable crosses the set point at Point C, the

sign of the error becomes negative. At this point, the integral term

winds down" at 16 times the tuned reset speed until the IVP reaches the

ARW low limit at Point D. The normal reset action is then resumed. The

fast reset speed quickly changes the magnitude of the integral term,

resulting in less process variable overshoot.

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Response Electronics CL6011B Especificaciones Pagina 40