3.3
Static characteristic (d3)
The static performance of the control valve is
affected by the friction hysteresis and the
elastic processes in the valve stem packing.
The static characteristic is plotted to check
the static performance. The analysis of
minimum, maximum and average dead
band parameters allows the control loop to
be evaluated.
To accomplish this, the reference variable w
is commanded in small steps and the re-
sponse of the controlled variable x is plotted
after waiting a predetermined period of
time.
This test
(
tESt d3
)
allows the full range of the
valve to be recorded in manual mode.
It is also possible to define a test range by
selecting the
Start
and
End
parameters. The
ascendent and descendent are plotted within
the test range.
100 measured points are plotted at the
maximum, i.e. max. 50 measured points are
available for the ascendent and the descen-
dent.
The step height and the number of measur-
ing points are determined automatically by
the adjusted test range. The dead zone is
analyzed by a step height smaller than
0.2 %.
The setpoint difference that causes a mini-
mal change in the valve position x is termed
dead band. It is recorded and analyzed in
the positioner for each step.
EB 8388 EN
25
Tests MAN
Fig. 13 · Static characteristic
