2.5.2 Hysteresis test (d5)
The hysteresis test allows changes in friction
to be analyzed and an alarm is issued when
a significant change in friction is detected.
If the diagnostic test d5 is activated and the
condition for the
Minimum time between
tests
parameter is met and the pressure con-
ditions have settled, the test is performed
with a change in travel < 1% to find
∆
y.
tESt
and
d5
appear on the positioner dis-
play in alternating sequence and
for
manual mode appears while the test is run-
ning.
The test is immediately canceled and the
positioner returns to automatic mode if the
valve travel leaves the tolerance band or a
change in the reference variable occurs
which is greater than the tolerance band set.
If the test was interrupted due to a change in
the reference variable, the test is started
again after waiting 30 seconds using the
new operating point.
If the test is canceled again at this point due
to a change in the reference variable
∆
w,
the test is started again after waiting 60 sec-
onds with the operating point.
This can happen ten times, during which the
time between tests is increased by 30 sec-
onds each time (30 s x Number of tests re-
peated).
After the test is canceled for the tenth time
(due to
∆
w), the time entered in
Minimum
time between tests
parameter is kept again.
The hysteresis test is deactivated by default.
We recommend activating the test after en-
tering
Minimum time between tests
by select-
ing
Start now
.
The
Minimum time between tests
and the
control parameters are stored in the
non-volatile memory of the positioner.
EB 8388 EN
17
Statistical information AUTO
Fig. 8 · Hysteresis test diagram
