A4.17.1 Shed_Opt; A4.18 Alarms; A4.18.1 Block Alarm (Block_Alm); A4.18.2 Process Alarms - YOKOGAWA vigilantplant EJA Series User Manual

A4.17 Mode Shedding upon Com-
puter Failure
When the data status of RCAS_IN or ROUT_IN,
which is the setting received from a computer as the
setpoint SP, falls to Bad while the PID block is
running in the RCas or ROut mode, the mode shedding
occurs in accordance with the settings in SHED_OPT.
If the RCAS_IN data is not renewed within the time
specified by SHED_RCAS in resource block, the data
status of RCAS_IN falls to Bad.

A4.17.1 SHED_OPT

The SHED_OPT setting stipulates the specifications of
mode shedding as shown below. Only one can be set.
Available Setting
Actions upon Computer Failure
for SHED_OPT
Normal shed, Sets MODE_BLK.actual to Cas*
normal return and leaves MODE_BLK.target unchanged.
Normal shed, Sets both MODE_BLK.actual and
no return MODE_BLK.target to Cas*
Shed to Auto, Sets MODE_BLK.actual to Auto*
normal return leaves MODE_BLK.target unchanged.
Shed to Auto, Sets both MODE_BLK.actual and
no return MODE_BLK.target to Auto*
Shed to Manual, Sets MODE_BLK.actual to Man, and
normal return leaves MODE_BLK.target unchanged.
Shed to Manual, Sets both MODE_BLK.actual and
no return MODE_BLK.target to Man.
Shed to retained If Cas is in MODE_BLK.target, sets
target, normal MODE_BLK.actual to Cas*
return MODE_BLK.target unchanged.
If Cas is not set in MODE_BLK.target,
sets MODE_BLK.actual to Auto*
leaves MODE_BLK.target unchanged.
Shed to retained If Cas is set in MODE_BLK.target, sets
target, no return both MODE_BLK.actual and
MODE_BLK.target to Cas*
If Cas is not set in MODE_BLK.target,
sets MODE_BLK.actual to Auto*
MODE_BLK.target to Cas.
*1 The modes to which a 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.
Lower priority
level
ROut RCas
*2 Only when Auto is set as permitted mode.
1
,
1
.
2
, and
2
.
1
, and leaves
2
, and
1
.
2
, and
TA0410.EPS
Higher priority
level
Cas Auto Man
FA0405.EPS
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

A4.18 Alarms

There are two kinds of alarms generated by a PID
block: block and process alarms.

A4.18.1 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.
Value of
BLOCK_ERR
Local Override MODE_BLK actual of PID block is LO.
Input Failure IN.status of the PID block is either of the
following:
Bad-Device Failure
Bad-Sensor Failure
Out of Service MODE_BLK.target of the PID block is O/S.

A4.18.2 Process Alarms

There are six types of process alarms. Only one
process alarm can be generated at the same 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
Cause of Occurrence
Alarm
HI_HI_ALM Occurs when the PV increases
above the HI_HI_LIM value.
HI_ALM Occurs when the PV increases
above HI_LIM value.
LO_ALM Occurs when the PV decreases
below the LO_LIM value.
LO_LO_ALM Occurs when the PV decreases
below the LO_LO_LIM value.
DV_HI_ALM Occurs when the value of
[PV - SP] increases above the
DV_HI_LIM value.
DV_LO_ALM Occurs when the value of
[PV - SP] decreases below the
DV_LO_LIM value.
A-21
APPENDIX 4. PID Block
Auto Cas.
Condition
TA0411.EPS
Parameter
Containing
Priority
Level Setting
HI_HI_PRI
HI_PRI
LO_PRI
LO_LO_LIM
DV_HI_PRI
DV_LO_PRI
TA0412.EPS
IM 01C22T02-01E