Response Electronics CL6011B Especificaciones descargar pdf (Pagina 272)

5Ć10 Configuration Tips

Original Ć June 1990CE4.2:CL6211

An IF TRUE SET function can be used just after a positive edge trigger

(PDET) function so that the control mode will not be locked. A rising

edge on the logic input to the PDET function will send a pulse to an IF

TRUE SET function which sets the mode of the loop. An operator station

or data highway command could then change the mode of the loop

because the IF TRUE SET function was not locked in the true state, only

pulsed to the true state.

5.7 Use Of Filtering In Override

Control Applications

Override control is a useful strategy for dealing with a variety of system

constraints so as to maximize operating unit efficiency or production, or

to ensure the safety of plant equipment and personnel.

Correct application of override control requires filtering of the track value

which is used as the integral term for the PID aglorithm in the overridden

upstream controller. This is accomplished by configuring the controller

to pass the track value through a first order filter. The filter time constant

is tuned to a value equal to the reciprocal of the reset action used in the

upstream controller, i.e. the filter action is adjusted according to the

dynamic characteristics of the controlled loops. The filter prevents the

possibility of substantial overshoot or undershoot in the control system's

response to a process disturbance.

The exact filtering technique used is dependant upon the dominant time

constant of each control loop, and the relative relationship between the

two loop time constants. The following sections provide guidelines for

implementing the various filtering techniques.

5.7.1 Use Of Filtering In Override Control On Loops With

Similar Dynamic Characteristics

Loops which have similar dynamic characteristics should make use of

track value filtering as previously described. The filter time constant is

tuned to a value equal to the reciprocal of the reset action used in the

upstream controller.

For example, consider two loops acting in an override control system,

where the loops are tuned as follows:

Gain = 0.3

Reset = 20.0 repeats / minute

Rate = 0.0

The user must filter the tracking value with a first order filter having a time

constant of 1/20.0, or 0.05 minutes. The DCPs FST must be configured

to provide the filtering action.

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Response Electronics CL6011B Especificaciones Pagina 272