OTT PLS User manual

English
Operating instructions
Pressure Probe OTT PLS

We reserve the right to make technical changes and improvements without notice.

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Table of contents
1 Scope of Supply 4
2 Order Numbers 4
3 Basic safety instructions 5
4 Introduction 6
5 Installing the pressure probe 8
5.1 Installation type A: fixing the pressure probe into a protective device 8
5.2 Installation type : hanging pressure probe 9
5.3 Connecting humidity absorbing system 10
5.4 Wire assignment of the pressure probe cable 10
5.5 Connecting the OTT PLS to any datalogger using an SDI-12 interface 11
5.6 Connecting the OTT PLS to any datalogger using a 4 … 20 mA interface 11
5.7 Determining the maximum load resistance at the 4 … 20 mA interface 11
5.8 Note on using the 4 … 20 mA interface 12
5.9 Note on using the RS-485 interface 12
6 SDI-12 Commands and Responses 13
6.1 Standard commands 13
6.2 Advanced SDI-12 commands 15
7 Carrying out maintenance work 20
8 Searching for disruptions/troubleshooting 21
9 Repair 22
10 Note about the disposal of old units 22
11 Technical Data 23
Appendix A – Connecting the OTT PLS to the OTT netDL or OTT DuoSens
datalogger using an SDI-12 or RS-485 interface 25
Appendix B – Connecting the OTT PLS to the OTT netDL or OTT DuoSens
datalogger using a 4 … 20 mA interface 28
Appendix C – Installing the OTT FAD 5 humidity absorbing system 30
Appendix D – Installing the OTT FAD 4PF humidity absorbing system 32
Appendix E – Note on Declaration of conformity 33

1 Scope of supply
䊳 OTT PLS – 1 Pressure probe with a ceramic, capacitive, relative pressure measuring cell
and shielded pressure probe cable with pressure compensation capillary and
Kevlar core for length stabilization. Pre-fabricated cable end with transport
protection against moisture.
– 1 Set of operating instructions
– 1 Factory acceptance test certificate (FAT)
2 Order numbers
䊳 OTT PLS OTT PLS pressure probe 63.037.001.9.0
– Version with 4 … 20 mA interface
– Version with SDI-12 interface
– Version with RS-485 interface (SDI-12 protocol)
Required order information
– Measuring range: 0 … 4 m;
0 … 10 m;
0 … 20 m;
0 … 40 m;
0 … 100 m
– Cable length: 1 … 200 m (with SDI-12 interface: 1 … 100 m)
䊳 Accessories Humidity absorbing system OTT FAD 4PF 63.025.021.4.2
– desiccant cartridge in clear container with connection
tube for pressure compensation capillary
Humidity absorbing system OTT FAD 5 63.037.025.3.2
– connecting box (pressure probe cable ↔connection cable
datalogger/voltage supply) with desiccant cartridge
Dessicant cartridge 97.100.066.4.5
– replacement cartridge in transport container
Cable attachment 96.140.173.9.5
Connection cable 97.000.040.9.5
– twisted pair construction; LiYY
– PVC, black
– 2 x 2 x 0.75 mm2
– unshielded
Connection cable 97.000.039.9.5
– twisted pair construction; FD CP (TP)
– PVC, gray
– 2 x 2 x 0.5 mm2
– shielded
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3 Basic safety information
䊳 Read these operating instructions before using the OTT PLS for the first time!
Make yourself completely familiar with the installation and operation of the
OTT PLS! Retain these operating instructions for later reference.
䊳 The OTT PLS is used for measuring the water level of ground and surface
waters in hydrometry. Only use the OTT PLS as described in these operating
instructions!
For further information, ➝ see Chapter 4, "Introduction".
䊳 Note all the detailed safety information given within the individual work steps.
All safety information in these operating instructions are identified with the
warning symbol shown here.
䊳 Ensure the electrical, mechanical, and climatic specifications listed in the
technical data are adhered to.
For further information ➝ see Chapter 11, "Technical data".
䊳 Do not make any changes or retrofits to the OTT PLS. If changes or retrofits are
made, all guarantee claims are voided.
䊳 Have a faulty OTT PLS inspected and repaired by our repair center. On no
account carry out repairs yourself!
For further information ➝ see Chapter 9, "Repair".
䊳 Dispose of the OTT PLS properly after taking out of service. On no account put
the OTT PLS into the normal household waste.
For further information ➝ see Chapter 10, "Note about the disposal of old
units".
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4 Introduction
The OTT PLS pressure probe is used for precisely measuring the water level of
ground and surface waters. The pressure probe uses the hydrostatic pressure of
the water column above a relative pressure measuring cell to do so. A pressure
compensation capillary in the pressure probe cable gives the measuring cell the
current ambient air pressure as a reference. Erroneous measurement results due to
atmospheric air pressure fluctuations are thus eliminated.
The OTT PLS can be supplied with various measuring ranges:
䊳0 … 4 m water column (0 ... 0.4 bar)
䊳0 … 10 m water column (0 ... 1 bar)
䊳0 … 20 m water column (0 ... 2 bar)
䊳0 … 40 m water column (0 ... 4 bar)
䊳0 … 100 m water column (0 ... 10 bar)
Furthermore, the pressure probe can be supplied with either an analog or digital
interface:
䊳 4 … 20 mA interface (with additional RS-485 interface
(SDI-12 protocol) for configuring the 4 … 20 mA interface*)
䊳 SDI-12 interface
䊳 RS-485 interface (SDI-12 protocol)
The pressure probe with the SDI-12/RS-485 interface can be configured via the
SDI-12 transparent mode of a datalogger. For example, a reference value or
offset value can be entered when starting up the device. With the 4 … 20 mA ver-
sion, it is possible to scale the measured value output to a smaller measuring
range using the additional RS-485 interface available (SDI-12 protocol).
A particular feature is that the pressure probe measures the water temperature as
well as the hydrostatic pressure of the water column and thus yields highly precise
and reproduceable measurement results by compensating the effects of temperature,
specific density of the water and the local gravitational acceleration at the specific
station. (For this, the specific density and local gravitational acceleration are
entered as required during startup.)
At the SDI-12 and RS-485 interfaces, the OTT PLS outputs either the water level
(compensated) or the hydrostatic pressure as well as the water temperature: at the
4 … 20 mA interface, either the water level (compensated) or hydrostatic pressure.
Measurement units can be set with SDI-12 commands as m / cm / ft (water level
measurement), mbar / psi (pressure measurement) and °C / °F (temperature mea-
surement).
The properties mentioned enable the universal operation of the pressure probe: for
example for connection to a datalogger, controlling pen recorders, alarm devices,
switching contacts, and, together with a display, for the display of measured values.
A humidity absorbing system for drying the surrounding air that enters the pressure
compensation capillary is available as an accessory.
* No parallel operation of the interfaces
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Fig. 1: Main layout of a water level station
with the OTT PLS pressure probe.
Pressure probe OTT PLS
Pressure-sensitive membrane
of the relative pressure
measuring cell
Cable suspension
(accessory)
Pressure probe cable
(e. g. to datalogger)
Pressure compensation
capillary
Attachment hooks
Water level
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5 Installing the pressure probe
The OTT PLS pressure probe can be used in a variety of ways, for example in
observation wells and boreholes from 1" diameter, in shafts, open waterways, and
in waterways that do not always hold water.
Caution
We do not recommend installing the pressure probe in the vicinity of port facilities,
industrial waste water discharges or areas with heavy chemical contamination.
The pressure probe is constructed from high-quality stainless steel and plastic.
However, depending on the mounting location, damaging corrosion can arise. For
more information on the materials used, see Chapter 11 "Technical data".
The pressure probe can be installed in two ways:
䊳 fixed in an individual protective device, built on location, or
䊳 hung on the pressure probe cable.
Caution
No moisture should be allowed to enter the pressure compensation capillary of the
pressure probe cable during installation! Very high air humidity can also lead to
the formation of water droplets in the pressure compensation capillary due to
temperature changes. These inevitably lead to unusable measurement results! As a
result, ensure the transport protection is left on the cable end during the whole
time it is being laid!
5.1 Installation type A: fixing the pressure probe into a protective
device
In flowing waters or waterways with a swell, the pressure probe must be fixed.
With strong currents (> 0.5 … 1 m/s) the hydrodynamic influences of the station
have to be considered in the installation. Depending on the version and mounting
of the individual components, overpressure or negative pressure can arise that can
affect the measurement result.
䡵 Determine the minimum and maximum water level at your station (e.g. staff
gauge, contact gauge). Use both values to specify the probe position. The
following conditions must be fulfilled:
– position the probe below the minimum water level if possible;
– difference between max. water level and position of the probe < measuring
range of the probe.
䡵 Fix the pressure probe according to your individual requirements in a protective
device, as shown in Figure 2, for example.
Note
The fine setting of the probe position is carried out, for example, by entering a
reference or offset value (with SDI-12/RS-485 interface) or using a scaling func-
tion of the datalogger connected.
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5.2 Installation type B: hanging pressure probe
See also Figure 1.
䡵 Determine the minimum and maximum water level at your station (e.g. staff
gauge, contact gauge). Use both values to specify the probe position. The follow-
ing conditions must be fulfilled:
– position the probe below the minimum water level if possible;
– difference between max. water level and position of the probe < measuring
range of the probe.
䡵 Fix the cable attachment (accessory) at a suitably sized attachment point.
䡵 Carefully lower the pressure probe on the pressure probe cable to the specified
depth. There are markings on the cable every 0.25 m to assist orientation.
䡵 Lay the pressure probe cable in the opened clamping jaws of the cable attach-
ment as shown in Figure 1 and secure the pressure probe cable by pushing the
clamping jaws together. The mechanical longitudinal stability required is pro-
vided by Kevlar fibers inside the pressure probe cable. Caution: maximum
hanging depth: 50 m. (greater depths on request).
Notes
䊳 The fine setting of the probe position is carried out, for example, by entering a
reference or offset value (with SDI-12/RS-485 interface) or using a scaling
function of the datalogger connected. It is thus sufficient in many applications
to position the probe approximately.
䊳 If the pressure probe cable ends in the immediate vicinity of the cable attach-
ment: fix the Kevlar fibers at a suitable point in addition!
Plastic protective tube
Fixing pin
OTT PLS
Fig. 2: Installation example of the OTT PLS
pressure probe in open waterways.
With waterways with currents or swell, a
fixing pin is used to securely fasten the
probe. Push the fixing pin through the
holes in the black protective cap.
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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 mm2(41 Ohm/1,000 m)
䊳 500 to 1,000 m cable length: 2 x 2 x 0.75 mm2 (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.
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