Switchpoint Optimisation - Endress+Hauser FEC 22 Betriebsanleitung

6 Additional Settings
Function
Caution!
Switch point
optimisation after
calibration with probe
uncovered
Switch point
optimisation after
calibration with probe
covered
Switch point difference
∆C for switch point
optimisation
Cleaning the vessel
Caution!
34
6.2 Switch point optimisation
After a calibration with uncovered or covered probe (see Section 5.2, 5.3 and 5.4)
the switch point of the FEC 22 can be set either manually (see Section 6.1) or
automatically to adjust to the material being measured.
Caution!
Switch point optimisation operates only with horizontal probes.
Switch point optimisation can be activated after an uncovered or covered probe
calibration has been carried out. The procedure for switch point optimisation is similar
to that for the simultaneous uncovered and covered probe calibrations. The
advantage of this procedure is that the second calibration point does not have to be
determined.
The evaluation electronics calculates the switch point and places it halfway between
the capacitance when empty (C
This optimises the signal-to-noise ratio. Error functions caused by changes in
capacitance due to build-up on the probe or to properties of the material
(conductivity, dielectric constant) are thus minimised.
After carrying out a calibration with probe uncovered, the capacitance when empty
C is permanently stored. When the probe is covered, the FEC 22 automatically
L
determines the capacitance with probe covered C
placed halfway between the capacitance when empty C
probe covered C . If the properties of the medium alter and cause a change in the
H
capacitance C when covering the probe, then this value is updated and the switch
H
point C adjusted accordingly.
S
After carrying out a calibration with probe covered, the capacitance with probe
covered C is permanently stored. When the probe is uncovered, the FEC 22
H
electronic insert automatically determines the empty capacitance C
C is then placed halfway between the capacitance when probe covered C
S
capacitance when probe uncovered C
cause a change in the capacitance C
updated and the switch point C
Switch point optimisation can also be activated with another ∆C value besides the
preset value ∆C = 2 pF. If the ∆C value was previously set manually to 4 pF,
then it is adjusted only when the change in capacitance C
than 2 x ∆C = 8 pF. When de-activating the switch point optimisation, the last
calculated switch point capacitance C
∆C is shown on the LED chain (rotary switch in Position 1). Changes can then be
made manually.
Caution!
If the vessel and probe are to be cleaned, e.g. CIP, with the switch point optimisation
switched on, then the switch point adjusts to the cleaning solution, provided that it
produces a larger change in capacitance than the process medium. This might
otherwise lead to faulty measurements. In this case switch point optimisation is not
recommended.
) and the capacitance with probe covered (C
L
. The switch point C
H
. If the properties of the medium alter and
L
when uncovering the probe, then this value is
L
adjusted accordingly.
S
is held and the current switch point difference
S
Elektronic insert FEC 22
).
H
is then
S
and capacitance when
L
. The switch point
L
and the
H
(see Page 26) is larger
X
Endress+Hauser