EB 8389-1S EN
69
Valve dead band
11
Valve dead band
The difference in set point w that causes a
minimal change in the valve position x is
termed ‘dead band’.
The valve dead band is affected by the fric-
tion hysteresis and the elastic processes in
the valve stem packing.
The test is started in the manual mode.
The positioner specifies the set point w in a
defined test range ('Lower range value' and
'Stop') in small steps and records the re
-
sponse of the valve position x after waiting a
'Waiting time after step change'. The step
height is determined automatically from the
number of measured values ('No. until re
-
versing') and the defined test range. The as
-
cendent and descendent are plotted within
the test range. The response of the valve po-
sition x to the change in set point (∆w) is
plotted in a graph.
The dead band is analyzed in the positioner
when a step height is smaller than 0.2 %.
−
'Mean dead band': Average change in
set point that causes a minimal change
in the valve position.
−
'Min. dead band': Minimum change in
set point that causes a minimal change
in the valve position.
−
'Max. dead band': Maximum change in
set point that causes a minimal change
in the valve position.
Fig. 16:
Diagnostics > Monitoring/tests > Dynamic tests >
Valve dead band