Coiltek CS-5100 Series Manual de instruções - Página 6

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Notes on Slack Loop Control

Uneven Drape Points

When the slack loop is draped from uneven positions as shown above, the loop valley will shift. It will

always shift toward the lower drape point as the valley rises, regardless of stock flow direction. Note

the valley center lines with a full loop and tighter loop and position the sensor between the two. The

goal is to get solid position signal through the working span desired.

A similar situation occurs when using the loop control between a process and an un-winder or winder.

The depletion or growth changes the tangential wrap point – also the drape point – as the line runs.

Hence, the valley of the loop will move over time.

Speed of Response

Most slack loop control applications govern variable-speed powered follower machinery. When this is

the case, a well-proportioned loop will yield better performance if the control range is larger. A

reasonable amount of vertical travel between far loop set point and near loop set point will nearly

always improve follower performance as the slack material buys time for the powered follower to

respond.

Since the loop control measures position but is used to coordinate velocity, it is by definition integral

control. The characteristics of integral control are zero long term error with modest speed of response.

Hence, the CS-5000 on its own works well for slow to moderate speed processes. For higher speed

applications, it must be used in conjunction with more sophisticated control systems that will improve

speed of response.