Micromod Micro-DCI: 53SL6000 Single Loop Controller Bedienungsanleitung PDF herunterladen (Seite 98)

8.6 Single Station Override Control

With Single Station Override Control, two standard

PID control loops function as two interdependent

variables, primary and limiting, to control a single

final element (e.g., valve). Neither variable may

exceed a safe limit. This control strategy is imple-

mented with the controller default settings and the

h.LiM or L.LiM (high or low limiting) control

schemes. The limiting control schemes are de-

faulted to use a value entered into cn.1-b1 parame-

ter as the second loop setpoint.

The primary loop of this control strategy is always

in control unless the output tries to exceed the high

(or low) limit imposed by the limiting loop. As a

high limit controller, the lowest output value is se-

lected to drive the final element via AO1. As a low

limit (high override) controller, the highest output is

selected to drive the final control element via AO1.

A typical high limit controller process application is

illustrated in Figure 8-12. In this application the

valve is normally adjusted in response to primary

variable (flow) disturbances unless the limiting vari-

able (pressure) loop has the highest output. When

this happens, the valve is closed to reduce pres-

sure. Pressure is the limiting variable because it is

the more critical value.

Figure 8-12. Single Station Override

Control Application

The signal connector is illustrated in Figure 8-13

and the connector pin assignment descriptions are

provided in the sections that follow. These sec-

tions also contain the applicable display prompts

that may require configuration changes.

Figure 8-13. Single Station Override

Control Signals

8.6.1 AI1 - Primary PV Input

This is the primary loop analog input signal value

that is compared to the primary loop setpoint to

determine the required primary output. The pri-

mary output is used as the 4-20 mA drive signal for

the final control element if the selector determines

the primary loop should have process control.

Applicable parameters that may require configura-

tion changes:

Section 5.2, conF-Ai.1-(SPan, ZEro, SQrt, bASE,

dFLt).

For PV alarms:

Section 7.7, conF-cn.1-(AiX, PL1, PL2, Adb).

8.6.2 AI2 - Limiting PV Input

This is the limiting loop analog input signal value

that is compared to the limiting loop setpoint. The

output drives the high/low limiter, which affects the

primary output 4-20 mA final control element sig-

nal.

Applicable parameters that may require configura-

tion changes:

Section 5.2, conF-Ai.2-(SPan, ZEro, SQrt, bASE,

dFLt).

8.6.3 DO1 - Primary PV High Alarm

Contact Out

D01 is closed (on) when the primary process vari-

able value is not within the loop 1 (cn.1) process

alarm limit 1 (PL1) setting.

Section 8. Eight Control Strategies 53SL6000 Instruction Manual

8-11

1 2 ... 93 94 95 96 97 98 99 100 101 102 103 ... 137 138

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