Yokogawa YVP110 - Manual (Page 86)

<16. PID Function Block>
16-5
IM 21B04C01-01E
Table 16.5 SHED_OPT of PID Block
Available
Setting for
SHED_OPT
Actions upon Computer Failure
Normal shed,
normal return
Sets MODE_BLK.actual to Cas* 1 ,
and leaves MODE_BLK.target
unchanged.
Normal shed, no
return
Sets both MODE_BLK.actual and
MODE_BLK.target to Cas* 1 .
Shed to Auto,
normal return
Sets MODE_BLK.actual to Auto* 2 ,
and leaves MODE_BLK.target
unchanged.
Shed to Auto, no
return
Sets both MODE_BLK.actual and
MODE_BLK.target to Auto* 2 .
Shed to Manual,
normal return
Sets MODE_BLK.actual to Man,
and leaves MODE_BLK.target
unchanged.
Shed to Manual,
no return
Sets both MODE_BLK.actual and
MODE_BLK.target to Man.
Shed to retained
target, normal
return
If Cas is set in MODE_BLK.target,
- sets MODE_BLK.actual to Cas* 1
and
- leaves MODE_BLK.target
unchanged.
If Cas is not set in MODE_BLK.
target,
- sets MODE_BLK.actual to Auto* 2
and
- leaves MODE_BLK.target
unchanged.
Shed to retained
target, no return
If Cas is set in MODE_BLK.target,
sets:
- MODE_BLK.actual to Cas, and
- MODE_BLK.target to Cas* 1 , too.
If Cas is not set in MODE_BLK.
target, sets:
- MODE_BLK.actual to Auto* 2 , and
- MODE_BLK.target to Cas.
*1: The modes to which the PID block can transfer are limited
to those set in MODE_BLK.permitted, and the priority
levels of modes are as shown below. In fact, if Normal
shed, normal return is set for SHED_OPT, detection of a
computer failure causes MODE_BLK.actual to change
to Cas, Auto, or Man, whichever is set in MODE_BLK.
permitted and has the lowest priority level.
Man
Auto
Cas
RCas
ROut
Higher priority level
Lower priority level
*2: Only when Auto is set as permitted mode.
NOTE: If a control block is connected as a cascade
primary block of the PID block in question, a mode
transition of the PID block to Cas occurs in the following
sequence due to initialization of the cascade connection:
RCas or ROut → Auto → Cas.
16.17 Alarms
There are two kinds of alarms generated by a PID
block: block and process alarms.
16.17.1 Block Alarm (BLOCK_ALM)
The block alarm BLOCK_ALM is generated upon
occurrence of either of the following errors (values
set in BLOCK_ERR) and notifies the content of
BLOCK_ERR.
Bit
Value of
BLOCK_ERR
Condition
4 Local Override MODE_BLK.actual of the PID
block is LO.
7 Input Failure The status of PV is Bad.
(The status of IN is Bad, or the
status of IN is Uncertain and
“Use Uncertain as Good” is false
in STATUS_OPTS).
15 Out of Service MODE_BLK.target of the PID
block is O/S.
16.17.2 Process Alarms
There are six types of process alarms. Only one
process alarm can be generated at a time, and
the process alarm having the highest priority level
from among those occurring at the same time is
generated. The priority level is set for each process
alarm type.
Process
Alarm
Cause of Occurrence
Parameter
Containing
Priority
Level
Setting
HI_HI_ALM Occurs when the PV
increases above the
HI_HI_LIM value.
HI_HI_PRI
HI_ALM Occurs when the PV
increases above HI_LIM
value.
HI_PRI
LO_ALM Occurs when the PV
decreases below the
LO_LIM value.
LO_PRI
LO_LO_ALM Occurs when the PV
decreases below the
LO_LO_LIM value.
LO_LO_LIM
DV_HI_ALM Occurs when the value
of [PV -SP] increases
above the DV_HI_LIM
value.
DV_HI_PRI
DV_LO_ALM Occurs when the value
of [PV -SP] decreases
below the DV_LO_LIM
value.
DV_LO_PRI