Yokogawa EJX930A - Manual (Page 124)

<Appendix 5. PID Block>
A5-6
IM 01C25T02-01E
Transition
Destination
Mode
Condition
NOT
Conditions
RCas* ** 7. If RCas is set in MODE_
BLK.target
- AND -
if neither IN.status (input
status) nor RCAS_
IN.status is Bad.
NOT if any
one or more
of conditions 1
to 3 are met.
ROut* ** 8. If ROut is set in MODE_
BLK.target
- AND -
if ROUT_IN.status (input
status) is not Bad.
NOT if any
one or more
of conditions 1
to 3 are met.
In accordance
with the
SHED_OPT
setting
9. If RCAS_IN.status or
ROUT_IN.status is Bad
(indicating a computer
failure; see Section A5.17.1
for details).
* 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.
A5.10 Bumpless Transfer
Prevents a sudden change in the control output
OUT at changes in block mode (MODE_BLK) and
at switching of the connection from the control
output OUT to the cascaded secondary function
block. The action to perform a bumpless transfer
differs depending on the MODE_BLK values.
A5.11 Setpoint Limiters
Active setpoint limiters that limit the changes in the
SP value, differ depending on the block mode as
follows.
A5.11.1 When PID Block Is in Auto Mode
When the value of MODE_BLK is Auto, the four
types of limiters are in force: high limit, low limit,
rate-of-increase limit, and rate-of-decrease limit.
Setpoint High/Low Limits
• A value larger than the value of SP_HI_LIM
cannot be set for SP.
• A value smaller than the value of SP_LO_LIM
cannot be set for SP.
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.
A5.11.2 When PID Block Is in Cas or RCas
Mode
By selecting Obey SP Limits if Cas or RCas in
CONTROL_OPTS (see Section A5.13), the setpoint
high/low limits can be put into force also when the
value of MODE_BLK is Cas or RCas.