Response Electronics CL6011B Dokumentacja Pobierz pdf (Strona 24)

3Ć4 Theory of Operation: Point Processing

Original Ć June 1990CE4.2:CL6211

first occurs, the output channels are held at their last output value. See

the User's Manual for a more complete description of the Trace Utility.

A controller which is in the Overload state is still processing inputs,

executing the FST instructions, and writing to the output channels.

However, this entire cycle takes longer than the allowed scan time for the

FST (normally one-quarter second) - therefore, there is no delay to the

start of the next cycle of events (that is scan inputs, FST, write outputs).

If this situation is sustained, the controller will report the overload

condition to the operator interface device(s).

3.2.2 Fast Scan Controllers

Certain models of the Computing and Interactive controllers are

designed to execute the FST and control algorithms at a rate faster than

the normal one-quarter second (4 Hz). These models operate at

one-tenth second (10 Hz) and one-twentieth second (20 Hz) scan

rates.

These models of the regulatory controllers may be needed for

applications which require extremely fast response times to changing

process conditions, such as pressure override, etc.

The architecture of the fast scan controllers is identical to the standard

regulatory controllers. That is, the input/output scanning and FST

execution are performed in the same sequence, and many of the

trade-offs and constraints apply equally to all models of the regulatory

controllers.

Note

Since the FST is executed more frequently on the fast

scan controllers, the control algorithm must be

simpler when implemented in a fast scan controller in

order to avoid an overload condition. THE FAST SCAN

CONTROLLERS ARE NORMALLY LIMITED TO

SUPPORTING FEWER POINTS AND/OR FEWER FST

STEPS THAN THE NORMAL SCAN RATE

CONTROLLERS.

The configuration device does not specifically

configure a fast scan version of the controllers.

Therefore, loading checks and point count limits are

not enforced by the configuration device.

For more detail concerning controller loading and estimation, please

refer to Appendix A, Loading and Sizing Calculations.

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Response Electronics CL6011B Dokumentacja Strona 24