Response Electronics CL6011B Especificaciones descargar pdf (Pagina 23)

3Ć3 Theory of Operation: Point Processing

Original Ć June 1990 CE4.2:CL6211

3.2 Point Processing

3.2.1 Data Acquisition

A configured controller performs the following operations in sequence:

1. Scan all inputs (discrete and analog) for current data.

2. Process the control algorithm and logic specified by the controller FST.

3. Output all data to the output channels (discrete and analog).

4. Wait for the next time to run the control logic (steps 1 through 3 above).

This method of input/output scanning isolates the FST, and the output

channels, from data value changes during the FST execution. That is, if

you read the same input channel at two different points within the FST,

you are assured to read the same value both times. Also, if you write to

the same output channel twice during the execution of an FST, only the

last value written will be detected at the output channel.

A similar isolation" of the communication channels is also performed

before and after the FST execution. This isolates the FST from data

change requests received from an operator during the execution of an

FST, such as Mode and SP changes. If an operating parameter is

changed by both the FST and the Operator during the time of a single

FST execution, the following forced precedence is enforced at the end of

the FST execution:

Operating Parameter Precedence

PV Control

SP Communications

IVP (Valve Output) Communications

Mode Control

Bias Control

Ratio Control

A side effect of this forced precedence is, if the control algorithm (FST)

repeatedly forces an operating parameter change to a point on

successive executions, the control algorithm can effectively lock out"

any operator changes to that operating parameter on that point. Details

of this situation are included in section 5.6 (page 5Ć9).

An unconfigured controller (current state is Database Hold" or No

Configuration") will still scan input channels, and force output channels;

however the control algorithm (FST) is not being executed. This allows

the Trace Utility to be used to examine controller input channels, and

force controller output channel values (output override) if needed. Also

note, when the transition from Normal Operating state to Database Hold

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Response Electronics CL6011B Especificaciones Pagina 23