Endress+Hauser Liquicap M FTI51 - Page 28

Installation Liquicap M FTI51, FTI52
28 Endress+Hauser
3.2.1 Measuring conditions
Minimum probe length for nonconductive media (<1μs/cm)
l
min
= ΔC
min
/ (C
s
* [εr - 1])
Notes!
• When installing in a nozzle, use inactive
length (L3).
• Probes with active buildup compensation
must be used for high-viscosity liquids that
tend to form buildup.
• Fully insulated rod and rope probes have to
be used for pump control (ΔS operation).
The switch-on and switch-off points are
determined by the empty and full
calibration.
– The maximum length depends on the
probe used.
A 16 mm rod, for example, generates a
capacitance of 380 pF/m in a conductive
liquid.
With a maximum span of 1600 pF, this
gives 1600pF/380pF per m = 4 m total
length. See also Page 81 ("Additional
capacitance")
• In the case of nonconductive media:
use a ground tube.
• The minimum change in capacitance for
level limit detection must be ≥ 5pF.
L00-FTI5xxxx-15-05-xx-xx-002
l
min
= Minimum probe length
ΔC
min
=5 pF
C
s
= Probe capacitance in air (see also → Page 81, "Additional capacitance")
εr = Dielectric constant e.g. oil = 2.0
L3
L3
L1
L1
MIN
MIN
s
s
off
off
on
on