IM 01E20F02-01E
A-36
APPENDIX 5. PID Block
A5.8 Feed-forward
Feed-forward is an action to add a compensation output
signal FF_VAL to the output of the PID control
computation, and is typically used for feed-forward
control. The figure below illustrates the action.
PID
computation
FF_SCALE
OUT_SCALE
PV
OUT
FF_VAL
FF_GAIN
FA0103.EPS
A5.9 Block Modes
The block mode is set in the parameter MODE-BLK.
Stipulates the target mode to which the
PID block transfers.
Indicates the current mode of the PID
block.
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.
Stipulates the mode in which the PID
block normally resides.
MODE_
BLK
Target
Actual
Permitted
Normal
TA0105.EPS
There are eight modes for a PID block as shown
below.
Block
Mode
Description
Remote output mode, in which the PID block outputs
the value set in ROUT_IN.
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.
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.
The PID block carries out automatic control and
outputs the result computed by the PID control
computation.
Manual mode, in which the PID block outputs the
value set by the user manually.
The PID block outputs the value set in TRK_VAL.
ROut
RCas
Cas
Auto
Man
LO
TA0106-1.EPS
Block
Mode
Description
Initialization and manual mode, in which the control
action is suspended. The PID block enters this mode
when the specified condition is met
(see Section A5.14).
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.
IMan
O/S
TA0106-2.EPS
A5.9.1 Mode Transitions
Transition
Destination
Mode
Condition
NOT
Conditions
1. If O/S is set in
MODE_
BLK.target
(or if O/S is set in
target
inside the resource
block)
2. If the specified condition is
met (see Section A5.14)
3. If Track Enable is specified in
CONTROL_OPTS
and the
value of
TRK_IN_D
is true
4. If Man is set in
MODE_
BLK.target
or if
IN.status
(input status) is Bad
5. If Auto is set in
MODE_
BLK.target
- AND -
if
IN.status
(input status) is
not Bad
6. If Cas is set in
MODE_
BLK.target
- AND -
if neither
IN.status
(input
status) nor
CAS_IN.status
is
Bad.
7. If RCas is set in
MODE_
BLK.target
- AND -
if neither
IN.status
(input
status) nor
RCAS_IN.status
is Bad.
8. If ROut is set in
MODE_
BLK.target
- AND -
if
ROUT_IN.status
(input
status) is not Bad
9. If
RCAS_IN.status
or
ROUT_
IN.status
is Bad (indicating a
computer failure; see Section
A5.17.1 for details)
NOT
if
condition 1
is met
NOT
if either
or both of
conditions 1
and 2 are met
NOT
if any
one or more
of conditions 1
to 3 are met
NOT
if any
one or more
of conditions 1
to 3 are met
NOT
if any
one or more
of conditions 1
to 3 are met
NOT
if any
one or more
of conditions 1
to 3 are met.
NOT
if any
one or more
of conditions 1
to 3 are met.
O/S
IMan
LO
Man
Auto*
Cas*
,
**
RCas*
,
**
ROut*
,
**
In accordance
with the
SHED_OPT
setting
TA0107.EPS
*
To activate mode transitions to Auto, Cas, RCas,
and ROut, the respective target modes must be set
beforehand to MODE_BLK.permitted.
**
A transition to Cas, RCas, or ROut requires that
initialization of the cascade connection has been
completed.
