78
EB 8389-1S EN
Partial stroke test (PST)
Note:
Cancel the test by right-clicking 'Can-
cel test' and selecting 'Execute' or by
pressing the rotary pushbutton at the
positioner. After the test has been can-
celed, the positioner remains in select-
ed mode. The 'PST status' reading in
-
dicates 'Not successful'.
In TROVIS-VIEW 4 the test information and
progress flag of the test are displayed. The
'Test information' status indicates 'Test not
active' after the test is finished.
Note concerning setting the PST diagnostic
parameters
−
We recommend only to start the partial
stroke test when the valve is in the end
position. In on/off valves, the start value
must be the same as the operating point.
−
The 'Ramp time (increasing)' must be
greater than the corresponding value for
'Min. transit time CLOSED' (Code 41)
determined during initialization.
−
The 'Ramp time (decreasing)' must be
greater than the corresponding value for
'Min. transit time OPEN' (Code 40) de
-
termined during initialization.
−
The 'Sampling time' must not be lower
than the indicated 'Recommended min.
sampling time'. The 'Recommended min.
sampling time' is calculated from the 'Ex
-
pected duration of test'.
12.1
Start triggered by the set
point
The partial stroke test of on/off valves is trig-
gered when the set point w moves in the
range between 25 and 50 % of the travel
and remains there for longer than six sec-
onds. See
u
The PST diagnostic parameter 'Lower range
value' must be within the defined position ±
'Tolerance limit' for the partial stroke test to
start.
The test and its cancelation are described in
section 12, while the test assessment is de-
scribed in
u
12.2
Start triggered by the
binary input
If the positioner is fitted with the optional bi
-
nary input, the partial stroke test can be
started by the binary input when the condi-
tions to start the partial stroke test are met:
−
A control valve is in the manual mode.
−
An on/off valve is in the manual or auto-
matic mode. In automatic mode, the test
is only started when the 'Safety set point'
is greater than the 'Fail-safe action limit'
(Code 49 - h2).
The test and its cancelation are described in
section 12, while the test assessment is de-
scribed in
u
It is important to make sure that the diag
-
nostic parameter 'Lower range value' of the
