Yokogawa YVP20S - Manual (Page 164)

17-3
IM 21B04C50-01E
<17. FAILSAFE HANDLING>
17.5 To Exit Failsafe
Failsafe cannot be cleared until the original cause is corrected. Determine the cause of
failure and correct it.
After the cause of the problem has been corrected, the Failsafe Dialog may show Clear
(Latched). Click the Clear latch button and close the Clear (Non-latch) button.
17.5.1 If the Deviation Error Failsafe is set
If the duration in which a deviation is out of the Error Band (%) exceeds the value of Time 2,
the failsafe action is activated.
Certain combinations of configuration parameters can complicate exiting failsafe. Typically
non-standard travel calibration coupled with tight shutoff, full open, and/or position limits
may need to be cleared before exiting failsafe. If the Time 2 (T2) Deviation parameters are
set the following four cases might be found for failsafe. Follow the steps as shown in below
for these cases.
● Deviation Error, Air to open, Low or high actuator pressure (Cases 1 and 3)
Table 17.1 Failsafe- Cases 1 and 3
T17.1eps
XD Error: Deviation error appears in the Error status.
The Failsafe Status dialog appears and shows Active (Latched).
Case 1
Case 3
Valve fails closed with low actuator pressure.
After the pressure problem is corrected, the valve is closed in failsafe.
XD Error: Deviation error appears in the Error status.
The Failsafe Status dialog appears and shows Active (Latched).
Failsafe type
Deviation Error
Actuator Action
Air to Open
Fail Close
Cause of Failure
High actuator pressure
Valve fails open with high actuator pressure.
After the pressure problem is corrected, the valve is closed in failsafe.
Failsafe type
Deviation Error
Actuator Action
Air to Open
Fail Close
Cause of Failure
Loss of supply or low actuator
pressure
Observable
behavior
Observable
behavior