EB 8389-1S EN
75
Partial stroke test (PST)
Cancelation conditions, time-out
−
'Max. test duration': The test is canceled
when the maximum permissible test du-
ration is reached.
−
'Max. breakaway time': The test is can
-
celed when the valve position has
reached less than 10 % of the PST target
travel after the defined time has elapsed.
This cancelation condition only becomes
effective after it has been activated ("Ac-
tivate 'Max. breakaway time" = [Yes]).
−
'Perm. time until step end': The test is
canceled when the time entered in 'Set
-
tling time before starting test' has
elapsed before the valve has reached its
'Stop' position. This cancelation condi
-
tion only becomes effective after it has
been activated ("Activate 'Perm. time un
-
til step end" = [Yes]).
Cancelation condition - valve position x (to
check the valve position)
−
'x monitoring value': The test is canceled
as soon as the valve position falls below
the adjusted value. This cancelation con-
dition only becomes effective after it has
been activated ('Activate x monitoring' =
Yes).
Cancelation condition, signal pressure Δp
out
−
'∆p out monitoring value': The test is
canceled if the change in signal pressure
exceeds or falls below the reference val-
ue.
The reference value is made up of 'Δp
out reference value' and 'Δp out moni
-
toring value'. This cancelation condition
only becomes effective after it has been
activated ('Activate Δp out monitoring' =
Yes).
The positioner determines the '∆p out
reference value' from both signal pres
-
sures issued at the start and end of the
step. It only applies to adjusted step
change and ramp values.
Cancelation condition, tolerance band
−
'PST tolerance band': The test is canceled
as soon as the deviation of the valve po-
sition (in relation to the step end value
(Stop)) exceeds the adjusted PST toler-
ance band. This cancelation condition
only becomes effective after it has been
activated ('Activate PST tolerance band
monitoring' = Yes).
Note:
−
The partial stroke test must be per-
formed with deactivated cancelation
conditions for valves with double-
acting actuator and pneumatic
booster as well as for valves that
have been initialized using the SUB
mode (substitute calibration).
−
Excessive overshooting may occur in
valves fitted with boosters. In this
case, the cancelation conditions 'x
monitoring value' and 'PST toler
-
ance band' must be increased ac-
cordingly.
Additionally, the partial stroke test is can-
celed when one of the following events aris-
es:
