5.3 Connecting humidity absorbing system
A humidity absorbing system must be installed for drying the surrounding air
that enters the pressure compensation capillary of the pressure probe cable!
See Appendix C and D.
Caution
Humidity entering the pressure compensation capillary leads to unusable
measurement results!
5.4 Wire assignment of the pressure probe cable
Caution
The factory assembled pressure probe cable should only be shortened with a suit-
able wire stripping tool! Danger of damaging the cable!
Recommendation: Store excess cable in loops if necessary!
If necessary, the pressure probe cable can be lengthened. For this purpose, use
a suitable junction box (e.g. OTT FAD 5). This should also be large enough to hold
the humidity absorbing system. The maximum cable length for the RS-485 inter-
face and the 4 … 20 mA interface is 1,000 m. Recommended cable type for the
RS-485 interface: shielded, twisted-pair cable. The wires intended for the power
supply can be twisted pair, but do not have to be. Recommended cable type for
the 4 … 20 mA interface: unshielded, low-voltage cable. If the additional RS-485
interface (configuring the 4 … 20 mA interface) is also to be fed to the datalog-
ger, a twisted pair cable is also necessary in this case.
Suitable wire sizes
䊳
Up to 500 m cable length: 2 x 2 x 0.5 mm
2
(41 Ohm/1,000 m)
䊳
500 to 1,000 m cable length: 2 x 2 x 0.75 mm
2
(27 Ohm/1,000 m)
Pressure compensation capillary
Cable shielding
Kevlar fibers
Pressure probe cable
Color Assignment
red +9,6 … 28 V DC
blue GND
gray SDI-12 Data
green RS-485 A
orange RS-485 B
Fig. 3: Wire assignment of the
OTT PLS pressure probe cable.
10
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