Siemens SITRANS L User guide

SITRANS L
Using SITRANS LR in a
Stilling Well
Application examples
04/2020
AG070814
Introduction
1
Applications
2
Advantages
3
Guidelines
4
Radar installation and
commissioning
requirements
5
Propagation factor
6
Using the CLEF position
detect parameter for
optimum accuracy
7

Siemens AG
Digital Industries
Postfach 48 48
90026 NÜRNBERG
GERMANY
Document order number: AG070814
Ⓟ
10/2020 Subject to change
Copyright © Siemens AG 2020.
All rights reserved
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subsequent editions.

Using SITRANS LR in a Stilling Well
Application examples, 04/2020, AG070814 3
Table of contents
1 Introduction .................................................................................................................................................4
1.1 Objective .............................................................................................................................................. 4
1.2 Disclaimer............................................................................................................................................ 4
2 Applications.................................................................................................................................................5
3 Advantages ..................................................................................................................................................6
4 Guidelines....................................................................................................................................................7
5 Radar installation and commissioning requirements ............................................................................9
6 Propagation factor................................................................................................................................... 10
7 Using the CLEF position detect parameter for optimum accuracy .................................................. 11

Using SITRANS LR in a Stilling Well
4Application examples, 04/2020, AG070814
Introduction
1
1.1 Objective
A stilling well, or by-pass pipe, is a conductive pipe used to create a quiet, stable
environment for a radar transmitter. These important guidelines will help you achieve
successful results when considering this type of application.
1.2 Disclaimer
Note
While
every effort is made to verify the following information, no warranty of accuracy or
usability is expressed or implied.

Using SITRANS LR in a Stilling Well
Application examples, 04/2020, AG070814 5
Applications
2
Applications that may benefit from a stilling well or by-pass pipe:
•Foaming and/or turbulent surfaces, such as a wet-well or an evaporator process.
•Very low dielectric liquids such as LPG, LNG, liquid nitrogen, or liquid oxygen.
•Applications where there are obstructions that are within the beam path of the radar
transmitter.

Using SITRANS LR in a Stilling Well
6Application examples, 04/2020, AG070814
Advantages
3
Signal to noise is improved in a stilling well.
•Signal strength is extremely high over the entire measurement range since no beam
spreading losses can occur in the stilling well.
•Material surfaces that would reflect poorly without the stilling well can be measured
reliably within the stilling well.
Example
The following example shows two echo profiles, both from a 25GHz radar device with a
2" horn antenna. The pink profile shows the use of a 2" diameter stilling well, and the
blue profile represents open space. The following observations can be made about the
stilling well profile:
•The echo from the target is significantly larger.
•Multiple echoes are larger and continue for a longer time. This is not a problem, as
the first echo algorithm component of the Process Intelligence signal processing will
select the first echo.

Using SITRANS LR in a Stilling Well
7Application examples, 04/2020, AG070814
Guidelines
4
Stilling well design guidelines
Please consider the following when setting up a still well:
•Pipe must be conductive.
Plastic pipes are not suitable.
•Smaller diameter pipes will yield better accuracy than larger diameter pipes.
Fewer propagation modes will exist, leading to more consistent echo shapes over the
measurement range.
•Choose larger diameter pipes if build-up is expected.
•Pipe should be one continuous length to avoid seams.
If a pipe connection is necessary, the internal seam must be as smooth as possible.
Ideally, the pipe should be cut off perfectly square, and an external coupling or collar
welded to the outside as shown in the accompanying diagram.

Guidelines
Using SITRANS LR in a Stilling Well
8Application examples, 04/2020, AG070814
•A vent hole must be provided near the top to prevent an air lock.
•Slots or holes in the pipe should be at least smaller than 1/10 of the diameter of
the pipe.
Slots or holes are common in pipes in the hydrocarbon industry to accommodate
either for the fact that the material in the tank isn’t homogeneous, or water could be
present at the bottom of the tank. Slots or holes will prevent the liquid from being
sucked in from the bottom.
•An angled plate welded to the bottom of the pipe will improve measurement
accuracy at the bottom of the tank for very low dielectric liquids.
Please refer to the accompanying illustration.

Using SITRANS LR in a Stilling Well
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Radar installation and commissioning
requirements
5
•A horn antenna will match better than a rod antenna for 6 GHz radar
transmitters.
This will result in lower noise levels on the signal as well as improved accuracy.
•Horn diameter must match the pipe diameter.
A horn diameter that is smaller than the pipe diameter could result in significant
measurement errors due to alternate mode interference.
•Obstructions in the pipe may include the vent connection, slots, or holes.
Orient the radar "e" field towards these obstructions to minimize their interference.
Bypass pipe installation
Still pipe installation
①Vent
②Align front or back of device with vents.
①Align front or back of device with still pipe slots.
②Slots

Using SITRANS LR in a Stilling Well
10 Application examples, 04/2020, AG070814
Propagation factor
6
The path of the signal in a pipe is not direct because it interacts with the internal pipe
walls resulting in a longer path for the radar signal. To compensate, the distance
calculation must use a speed factor that is slower than the speed of light. This
propagation speed factor is dependent upon the pipe diameter and the frequency used.
Refer to the device instruction manual for a table that lists the necessary propagation
factors according to the various pipe diameters.
Propagation factor values for various pipe diameters
40 mm
50 mm
80 mm
100 mm
150 mm
200 mm
5.8 GHz
0.7953
0.9254
0.9530
0.9794
0.9884
25 GHz
0.9844
0.988
0.9935
0.9965