as a bar graph. Ideally, the setpoint devia-
tion should be as small as possible.
Similar to the valve travel histogram, the
Setpoint deviation histogram
folder contains
long-term data, i.e. measured data are up-
dated cyclically (scan rate 1 s) over the en-
tire positioner service life and stored every
24 hours in the positioner’s non-volatile
memory for long-term monitoring.
Additional information determined from this
long-term histogram are shown in Fig. 5.
The minimum and maximum setpoint devia-
tions are also indicated.
In order to obtain a summary of recent
setpoint deviations, the last 100 setpoint de-
viations are logged at an adjustable scan
rate (default: 1 s) and saved in an FIFO
memory.
The scan rate can be changed in the
Scan
rate short time
parameter. On changing the
scan rate, old data in the short-term histo-
gram are deleted.
The
Average values e short
parameter indi-
cates the class in which the last 100 mea-
sured setpoint deviations were stored on av-
erage in the FIFO memory.
Data can be reset in the
Status messages
folder.
2.4
Cycle counter histogram
The histogram shows the span of cycles the
valve has moved through and the frequency
of the cycles.
A valve cycle starts at the point where the
valve stroke changes direction until the point
where it changes direction again. The valve
stroke between these two changes in direc-
tion is the cycle span.
The cycle counter histogram provides a sta-
tistical analysis of the cycles. As a result, the
cycle counter also provides information on
the dynamic stress of a bellows seal or
packing.
EB 8388 EN
13
Statistical information AUTO
Fig. 5 · Setpoint deviation histogram