A8.7 Control Action Bypass; A8.8 Feed-Forward; A8.9 Block Modes - YOKOGAWA digitalYEWFLO Series User Manual

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.
CAS_IN
Setpoint
RCAS_IN
Control
SP
IN PV
Filter

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 figure illustrates the action.
PID
PV
computation
BYPASS
Output OUT
Feed-
forward
FA0804.ai
FF_VAL
FF_SCALE
OUT_SCALE
FF_GAIN
OUT
FA0805.ai
<APPENDIX 8. PID BLOCK>

A8.9 Block Modes

The block mode is set in the parameter MODE_
BLK.
MODE_ Target Stipulates the target mode to which the
BLK 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 Description
Mode
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 fieldbus 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 specified condition is met (Read 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.
A8-5
IM 01F06F00-01EN