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A8.7 control action bypass, A8.8 feed-forward, A8.9 block modes – Yokogawa digitalYEWFLO (DY-FF) User Manual

Page 131: A8.7 control, Action, Bypass, A8-5, A8.9 block, Modes

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A8-5

IM 01F06F00-01EN

A8.7 Control Action Bypass

The PID control computation can be bypassed so
as to set the SP value in the control output OUT as
shown below. Setting BYPASS to “On” bypasses
the PID control computation.

Setpoint

Control

Feed-

forward

CAS_IN

Filter

IN

PV

BYPASS

SP

RCAS_IN

Output

OUT

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A8.8 Feed-forward

Feed-forward is an action to add a compensation
input signal FF_VAL to the output of the PID control
computation, and is typically used for feed-forward
control. The following fi gure illustrates the action.

PID

computation

FF_SCALE

OUT_SCALE

PV

OUT

FF_VAL

FF_GAIN

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A8.9 Block Modes

The block mode is set in the parameter MODE_
BLK.

MODE_
BLK

Target

Stipulates the target mode to which the
PID block transfers.

Actual

Indicates the current mode of the PID
block.

Permitted Stipulates all the modes that the PID

block can enter. The PID block is
prohibited to enter any mode other than
those set in this element.

Normal

Stipulates the mode in which the PID
block normally resides.

There are eight modes for a PID block as shown
below.

Block

Mode

Description

ROut Remote output mode, in which the PID block outputs

the value set in ROUT_IN.

RCas Remote cascade mode, in which the PID block carries

out the PID control computation based on the setpoint
(SP) set via the remote cascade connection, such as
from a computer, and outputs the computed result.

Cas

Cascade mode, in which the PID block carries out the
PID control computation based on the setpoint (SP) set
from another fi eldbus function block, and outputs the
computed result.

Auto

The PID block carries out automatic control and outputs
the result computed by the PID control computation.

Man

Manual mode, in which the PID block outputs the value
set by the user manually.

LO

The PID block outputs the value set in TRK_VAL.

IMan Initialization and manual mode, in which the control

action is suspended. The PID block enters this
mode when the specifi ed condition is met (Refer to
APPENDIX 8.14 “Initialization and Manual Fallback
(IMAN)”).

O/S

Out of service mode, in which neither the control
computation nor action is carried out, and the output is
kept at the value that was output before the PID block
entered into O/S mode.