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!
The humidity absorbers OTT FAD 4PF and OTT FAD 6 are available as acces-
sories (see Chapter 2, "Accessories"). The OTT FAD 6 humidity absorber also
serves as connection box (pressure probe cable connection cable data log-
ger/voltage supply).
■
Install the humidity absorber at a dry place and connect the pressure compen-
sation capillary to the humidty absorber; observe the operating instructions of
the humidity absorber used!
Please note:
Humidity entering the pressure compensation capillary of the pres-
sure probe cable leads to unusable measurement results!
5.4 Wire assignment of the pressure probe cable
Please note:
The factory assembled pressure probe cable should only be short-
ened with a suitable wire stripping tool (see accessories)! Danger of damaging the
cable! Recommendation: if required, store a slightly too long pressure probe cable
in loops – taking into account the minimum bending radius. Find instructions how
to shorten the pressure probe cable in Annex A.
If necessary, the pressure probe cable can be lengthened. For this purpose, use a
suitable junction box (e.g. humidity absorber OTT FAD 6). This should be large
enough to hold the humidity absorbing system! The maximum cable length for the
RS-485 interface is 1,000 m; for the SDI-12 interface 200 m! Recommended cable
type for the RS-485 interface: twisted pair cable (paired stranded wires); shielded.
The wires provided for the voltage supply can, but do not have to be twisted
pairs. Recommended cable type for the SDI-12 interface: unshielded low-voltage
cable.
Suitable wire sizes:
▶
up to 500 m cable length: 2 x 2 x 0.5 mm
2
(41 Ohm/1000 m)
▶
500 to 1000 m cable length: 2 x 2 x 0.75 mm
2
(27 Ohm/1000 m)
Fig. 3: Wire assignment
of the OTT PLS 500 pressure probe cable.
Note:
The pressure probe cable has a
cable shield which is shortened to the cable
sheath at the factory during stripping. The
cable shield must not be connected to
earth/ground when installing the
OTT PLS 500!
Pressure compensation capillary
Pressure probe cable
Color Assignment
red +5.5
…
+28.8
V
DC
blue GND
grey SDI-12
Data
green RS-485
A
orange RS-485
B
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