Yokogawa digitalYEWFLO (DY-FF) - Manual (Page 133)

A8-7
IM 01F06F00-01EN
A8.12 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 fi gure 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
FA0806.EPS
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 specifi ed in
CONTROL_OPTS.
A8.13 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
primary 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.
• CONTROL_OPTS
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.
A8.14 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.