Yokogawa Wireless Temperature Transmitter YTA510 - Manual (Page 85)

<Appendix 4. PID Block>
A4-9
IM 01C50T02-01E
A4.17 Mode Shedding upon
Computer 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.
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 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
M ODE_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 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
both MODE_BLK.actual and MODE_
BLK.target to Cas* 1 . 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 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.
FA0405.ai
Higher priority
level
Lower priority
level
ROut RCas Cas Auto Man
*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.
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
Condition
Input Failure IN.status of the PID block is either of
the following:
• Bad-Device Failure
• Bad-Sensor Failure
Local Override MODE_BLK.actual of the PID block
is LO.
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
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_PRI
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