Yokogawa Wireless Temperature Transmitter YTA510 - Manual (Page 83)

<Appendix 4. PID Block>
A4-7
IM 01C50T02-01E
Setpoint Rate Limits
The setpoint rate limits are used to restrict the
magnitude of changes in the SP value so as to
change the SP value gradually towards a new
setpoint.
• An increase of the SP value at each execution
period (period of execution in the Block Header)
is limited to the value of SP_RATE_UP.
• A decrease of the SP value at each execution
period (period of execution in the Block Header)
is limited to the value of SP_RATE_DOWN.
A4.11.2 When PID Block Is in Cas or RCas
Mode
By selecting Obey SP Limits if Cas or RCas in
CONTROL_OPTS (see Section A4.13), the setpoint
high/low limits can be put into force also when the
value of MODE_BLK is Cas or RCas.
A4.12 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
FA0404.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.
A4.13 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.