Yokogawa EJX930A - Manual (Page 123)

<Appendix 5. PID Block>
A5-5
IM 01C25T02-01E
A5.7 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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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
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A5.9 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 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 (see Section A5.14).
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.
A5.9.1 Mode Transitions
Transition
Destination
Mode
Condition
NOT
Conditions
O/S 1. If O/S is set in MODE_
BLK.target (or if O/S is
set in target inside the
resource block).
IMan 2. If the specified condition is
met (see Section A5.14).
NOT if
condition 1 is
met.
LO 3. If Track Enable is specified
in CONTROL_OPTS and
the value of TRK_IN_D
is true.
NOT if either
or both of
conditions 1
and 2 are met.
Man 4. If Man is set in MODE_
BLK.target or if IN.status
(input status) is Bad.
NOT if any
one or more of
conditions 1 to
3 are met.
Auto* 5. If Auto is set in MODE_
BLK.target
- AND -
if IN.status (input status) is
not Bad.
NOT if any
one or more of
conditions 1 to
3 are met.
Cas* ** 6. If Cas is set in MODE_
BLK.target
- AND -
if neither IN.status (input
status) nor CAS_IN.status
is Bad.
NOT if any
one or more of
conditions 1 to
3 are met.