Yokogawa EJX930A - Manual (Page 125)

<Appendix 5. PID Block>
A5-7
IM 01C25T02-01E
A5.12 External-output Tracking
External tracking is an action of outputting the value
of the remote output TRK_VAL set from outside
the PID block, as illustrated in the figure below.
External tracking is performed when the block
mode is LO.
TRK_SCALE
OUT_SCALE
TRK_VAL
OUT
TRK_IN_D
LO mode
PID control
computation result
FA0504.ai
To change the block mode to LO:
(1) Select Track Enable in CONTROL_OPTS.
(2) Set TRK_IN_D to true.
However, to change the block mode from Man
to LO, Track in Manual must also be specified in
CONTROL_OPTS.
A5.13 Measured-value Tracking
Measured-value tracking, also referred to as SP-PV
tracking, is an action to equalize the setpoint SP
to the measured value PV when the block mode
(MODE_BLK.actual) is Man in order to prevent a
sudden change in control output from being caused
by a mode change to Auto.
While a cascade primary control block is performing
the automatic or cascade control (in the Auto or
Cas mode), when the mode of its secondary control
block is changed from Cas to Auto, the cascade
connection is opened and the control action of the
primary block stops. The SP of the secondary
controller can be equalized to its cascade input
signal CAS_IN also in this case.
The settings for measured-value tracking are made
in the parameter CONTROL_OPTS, as shown in
the table below.
Options in
CONTROL_OPTS
Description
Bypass Enable This parameter allows BYPASS to
be set.
SP-PV Track in
Man
Equalizes SP to PV when MODE_
BLK.target is set to Man.
SP-PV Track in
ROut
Equalizes SP to PV when MODE_
BLK.target is set to ROut.
SP-PV Track in LO
or IMan
Equalizes SP to PV when actual is
set to LO or IMAN.
SP-PV Track
retained Target
Equalizes SP to RCAS_IN when
MODE_BLK.target is set to RCas,
and to CAS_IN when MODE_BLK.
target is set to Cas when the
actual mode of the block is IMan,
LO, Man or ROut.
Direct Acting Set the PID block to a direct acting
controller.
Track Enable This enables the external tracking
function.
The value in TRK_VAL will replace
the value of OUT if TRK_IN_D
becomes true and the target mode
is not Man.
Track in Manual This enables TRK_VAL to replace
the value of OUT when the target
mode is Man and TRK_IN_D is
true. The actual mode will then be
LO.
Use PV for
BKCAL_OUT
Sets the value of PV in BKCAL_
OUT and RCAS_OUT, instead of
the value of SP.
Obey SP limits if
Cas or RCas
Puts the setpoint high/low limits in
force in the Cas or RCas mode.
No OUT limits in
Manual
Disables the high/low limits for
OUT in the Man mode.
A5.14 Initialization and Manual
Fallback (IMan)
Initialization and manual fallback denotes a set of
actions in which a PID block changes mode to IMan
(initialization and manual) and suspends the control
action. Initialization and manual fallback takes
place automatically as a means of abnormality
handling when the following condition is met:
• The quality component of BKCAL_IN.status is
Bad.
- OR -
• The quality component of BKCAL_IN.status is
Good (c)
- AND -
The sub-status component of BKCAL_IN.status
is FSA, LO, NI, or IR.
The user cannot manually change the mode to
IMan. A mode transition to IMan occurs only when
the condition above is met.