Process Control - Radar Level Transmitters, Model 353X - Lab-Volt

Process Control - Radar Level Transmitters, Model 353X - Lab-Volt
Process Control
Radar Level Transmitters
Instructor Guide
52200-10
Order no.:
52200-10
First Edition
Revision level: 09/2015
By the staff of Festo Didactic
© Festo Didactic Ltée/Ltd, Quebec, Canada 2015
Internet: www.festo-didactic.com
e-mail: did@de.festo.com
Printed in Canada
All rights reserved
ISBN 978-2-89747-453-9 (Printed version)
ISBN 978-2-89747-456-0 (CD-ROM)
Legal Deposit – Bibliothèque et Archives nationales du Québec, 2015
Legal Deposit – Library and Archives Canada, 2015
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Safety and Common Symbols
The following safety and common symbols may be used in this manual and on
the equipment:
Symbol
Description
DANGER indicates a hazard with a high level of risk which, if not
avoided, will result in death or serious injury.
WARNING indicates a hazard with a medium level of risk which,
if not avoided, could result in death or serious injury.
CAUTION indicates a hazard with a low level of risk which, if not
avoided, could result in minor or moderate injury.
CAUTION used without the Caution, risk of danger sign ,
indicates a hazard with a potentially hazardous situation which,
if not avoided, may result in property damage.
Caution, risk of electric shock
Caution, hot surface
Caution, risk of danger
Caution, lifting hazard
Caution, hand entanglement hazard
Notice, non-ionizing radiation
Direct current
Alternating current
Both direct and alternating current
Three-phase alternating current
Earth (ground) terminal
© Festo Didactic 52200-10
III
Safety and Common Symbols
Symbol
Description
Protective conductor terminal
Frame or chassis terminal
Equipotentiality
On (supply)
Off (supply)
Equipment protected throughout by double insulation or
reinforced insulation
In position of a bi-stable push control
Out position of a bi-stable push control
IV
© Festo Didactic 52200-10
Table of Contents
Preface ................................................................................................................. VII About This Manual ................................................................................................ IX To the Instructor .................................................................................................... XI Exercise 1 Fundamentals of Radar Level Transmitters ............................... 1 DISCUSSION ...................................................................................... 1 Introduction ............................................................................... 1 How do radar level sensors work? ........................................... 2 Measuring a level ........................................................................ 3 Blocking distance ........................................................................ 4 Dielectric constant ....................................................................... 4 Echo ............................................................................................ 4 What is the difference between a horn-antenna radar level
sensor and a guided-radar level sensor? ................................. 5 Advantages and limitations ....................................................... 6 Characteristics of the supplied radar level transmitter ............. 7 Remote display keys ................................................................... 8 Summary of technical specifications ........................................... 9 Characteristics of the supplied guided-radar level
transmitter ............................................................................... 10 Remote display keys ................................................................. 11 Summary of technical specifications ......................................... 12 Installing a radar level transmitter ........................................... 12 Commissioning a radar level transmitter ................................ 12 Advanced process conditions .................................................... 12 Reset of the transmitter ............................................................. 13 Linearization .............................................................................. 14 Echo envelope curve ................................................................. 14 Correction offset ........................................................................ 15 PROCEDURE.................................................................................... 16 Set up and connections .......................................................... 16 Commissioning the level transmitter....................................... 20 Adding an offset ...................................................................... 24 Displaying level in percentage of span ................................... 29 How to obtain a volume reading ............................................. 31 Calculating the max. scale parameter ....................................... 31 Making a new mapping ........................................................... 32 Making a new mapping with the radar level transmitter............. 32 Making a new mapping with the guided-radar level
transmitter ................................................................................. 33 Appendix A Configuring the Transmitter, Model 46931, Using
FieldCare ...................................................................................... 35 Setup....................................................................................... 39 Making a new mapping ........................................................... 44 Adding an offset ...................................................................... 46 © Festo Didactic 52200-10
V
Table of Contents
Appendix B Configuring the Transmitter, Model 46932, Using
FieldCare ...................................................................................... 49 Setup....................................................................................... 53 Making a new mapping ........................................................... 59 Adding an offset ...................................................................... 62 Appendix C Configuring the Transmitter, Model 46931, Using
DeviceCare ................................................................................... 65 Setup....................................................................................... 72 Making a new mapping ........................................................... 77 Adding an offset ...................................................................... 80 Appendix D Configuring the Transmitter, Model 46932, Using
DeviceCare ................................................................................... 83 Setup....................................................................................... 90 Making a new mapping ........................................................... 96 Adding an offset .................................................................... 100 Index................................................................................................................... 103 VI
© Festo Didactic 52200-10
Preface
Automated process control offers so many advantages over manual control that
the majority of today’s industrial processes use it to some extent. Breweries,
wastewater treatment plants, mining facilities, and the automotive industry are
just a few industries that benefit from automated process control systems.
Maintaining process variables such as pressure, flow, level, temperature, and pH
within a desired operating range is of the utmost importance when manufacturing
products with a predictable composition and quality.
The Instrumentation and Process Control Training System, series 353X, is a
state-of-the-art system that faithfully reproduces an industrial environment.
Throughout this course, students develop skills in the installation and operation
of equipment used in the process control field. The use of modern, industrialgrade equipment is instrumental in teaching theoretical and hands-on knowledge
required to work in the process control industry.
The modularity of the system allows the instructor to select the equipment
required to meet the objectives of a specific course. Two mobile workstations, on
which all of the equipment is installed, form the basis of the system. Several
optional components used in pressure, flow, level, temperature, and pH control
loops are available, as well as various valves, calibration equipment, and
software. These add-ons can replace basic components having the same
functionality, depending on the context. During control exercises, a variety of
controllers can be used interchangeably depending on the instructor’s
preference.
We hope that your learning experience with the Instrumentation and Process
Control Training System will be the first step toward a successful career in the
process control industry.
© Festo Didactic 52200-10
VII
Preface
VIII
© Festo Didactic 52200-10
About This Manual
Safety considerations
Safety symbols that may be used in this manual and on the equipment are listed
in the Safety Symbols table at the beginning of the manual.
Safety procedures related to the tasks that you will be asked to perform are
indicated in each exercise.
Make sure that you are wearing appropriate protective equipment when
performing the tasks. You should never perform a task if you have any reason to
think that a manipulation could be dangerous for you or your teammates.
Systems of units
Units are expressed using the International System of Units (SI) followed by the
units expressed in the U.S. customary system of units (between parentheses).
© Festo Didactic 52200-10
IX
To the Instructor
You will find in this Instructor Guide all the elements included in the Student
Manual together with the answers to all questions, results of measurements,
graphs, explanations, suggestions, and, in some cases, instructions to help you
guide the students through their learning process. All the information that applies
to you is placed between markers and appears in red.
Accuracy of measurements
The numerical results of the hands-on exercises may differ from one student to
another. For this reason, the results and answers given in this manual should be
considered as a guide. Students who correctly performed the exercises should
expect to demonstrate the principles involved and make observations and
measurements similar to those given as answers.
© Festo Didactic 52200-10
XI
Sample Exercise
Extracted from
the Student Manual
and the Instructor Guide
Exercise
1
Fundamentals of Radar Level Transmitters
EXERCISE OBJECTIVE
Understand the fundamentals of radar level measurement and be able to install
and configure a radar level sensor for accurate level measurement.
DISCUSSION OUTLINE
The Discussion of this exercise covers the following points:


Introduction How do radar level sensors work? 


What is the difference between a horn-antenna radar level sensor and a
guided-radar level sensor? Advantages and limitations Characteristics of the supplied radar level transmitter 
Characteristics of the supplied guided-radar level transmitter 

Installing a radar level transmitter Commissioning a radar level transmitter Measuring a level. Blocking distance. Dielectric constant. Echo.
Remote display keys. Summary of technical specifications.
Remote display keys. Summary of technical specifications.
Advanced process conditions. Reset of the transmitter. Linearization.
Echo envelope curve. Correction offset.
DISCUSSION
Instrument symbols
Radar Level Transmitter
Introduction
Radar level sensors use high-frequency electromagnetic waves to detect the
level of liquids or solids in different types of containers such as tanks, silos, or
even a lake. Radar level measurement devices are either contact sensors or
non-contact sensors. Since radar level sensors have no moving parts, they
require very low maintenance. Figure 1 shows two level-measurement
applications using radar level sensors. The first application (Figure 1a) is a liquid
level-measurement application using a non-contact radar level sensor. The
second application (Figure 1b) is a solid level-measurement application using a
guided-radar level sensor. The differences between the two types of sensors are
presented later in this discussion.
Guided-Radar Level
Transmitter
© Festo Didactic 52200-10
1
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
(a)
(b)
Figure 1. Typical applications of radar level sensors.
Unlike ultrasonic level sensors, radar level sensors are not very sensitive to
temperature changes. However, they are sensitive to changes in the value of the
dielectric constant of the medium being measured. Changes in the dielectric
constant may have an influence on the quality of the level detection since radar
level sensors are strongly dependent on the quality of the electromagnetic waves
reflected by the process liquid or solid. The reflected waves are called the echo.
The intensity of the echo is inversely proportional to the square of the distance
between the sensor and the surface of the substance. Thus, the farther the
sensor is from the surface of the measured substance, the weaker the echo. The
quality of the echo is also reduced by the absorption of the electromagnetic
waves by vapor, mist, foam, or dust. The electromagnetic waves can also be
reflected by other apparatuses, such as inlets or other sensors, in the detection
path of the sensor. An echo suppression system usually reduces these extra
reflections.
How do radar level sensors work?
You are already familiar with some types of electromagnetic radiations. Visible
light, radio waves, and microwaves are all examples of electromagnetic
radiations. Radar level sensors use electromagnetic waves with a frequency
between 100 MHz and 30 GHz (i.e., microwaves) to measure levels. They use
what is called the time-of-flight method. The sensor sends a microwave pulse
toward the bottom of the vessel and, from the time it takes for the pulse to return,
it calculates the distance between the sensor and the surface of the medium. The
main difference between a radar level sensor and a guided-radar level sensor is
that the later use a probe to guide the microwave pulse to the medium surface
instead of an antenna. Figure 2 shows the relevant dimensions for a typical radar
level sensor and for a guided-radar level sensor.
2
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Probe
length
(b) Guided-radar level sensor.
(a) Radar level sensor.
Figure 2. Relevant dimensions.
In this figure, F is the span or full distance in which measurements take place, E
is the total distance between the sensor mounting flange and the lowest
measureable level of the span, L is the portion of E currently filled with the
product, D is the portion of E which is empty, and BD is the blocking distance.
For a radar level sensor with a horn antenna, the emitting angle α can be used
to calculate the detection radius for a given height.
Measuring a level
The radar level sensor can measure the time it takes for a high-frequency
electromagnetic pulse to go back and forth from the sensor to the surface of the
substance. Since electromagnetic waves travel at the speed of light, it is easy to
calculate the distance from the sensor to the medium surface using Equation (1).
∙
2
where
(1)
is the distance between the sensor and the medium surface
is the speed of light, about 300 000 000 m/s (984 000 000 ft/s)
is the time it takes for the microwave pulse to go back and forth from
the sensor to the surface of the substance
Since the empty distance (E) is programmed when setting up the sensor, the
level in the vessel cans easily be calculated using Equation (2).
(2)
where
© Festo Didactic 52200-10
is the level
is the empty distance
is the distance between the sensor and the medium surface
3
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Blocking distance
Most radar sensors have a minimum distance that must be respected between
the maximum level and the mounting flange of the sensor. This distance is called
the blocking distance. Within the blocking distance the measurement is not
reliable. Therefore, the level of the product must not be allowed to rise within the
blocking distance.
Dielectric constant
When measuring the level of a liquid or solid using a radar sensor, the dielectric
constant (or relative static permittivity) of the substance has an influence on how
much of the microwave pulse is reflected back to the sensor. A medium with a
high dielectric constant, such as water, strongly reflects the pulse. A substance
with a low dielectric constant produces a weaker reflection.
With a guided-radar level detector, the sensitivity to variations in the dielectric
constant can be used to measure the distance to the interface of two substances
with different dielectric constants as illustrated in Figure 3.That is, the sensor can
measure the thickness of the two layers of liquid, as well as the total level of
liquid in the tank.
Total
level
Interface
level
Figure 3. Measuring the distance to the interface of two liquids using a guided-radar level
sensor.
Echo
As mentioned above, the echo is the portion of the electromagnetic pulses that
travels back to the sensor when reflected at the interface between the air and
the medium.
To measure a level, the sensor must be able to detect the echo. Therefore, the
echo must have a sufficient intensity to be detected. Many factors influence the
intensity of the echo. The most important ones are related to the propagation,
absorption, and reflection of the electromagnetic waves. Electromagnetic waves
naturally disperse as they propagate and their intensity is inversely proportional
4
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
to the square of the distance traveled. The more distance there is between the
sensor and the surface of the product, the weaker the intensity of the echo will
be. When an electromagnetic pulse hits the surface of the product, a portion of its
energy is absorbed by the product instead of being reflected, thus diminishing the
intensity of the returning wave. A sharp transition between the air and the
medium is advisable to obtain reliable measurements. Foam, for example, can
cause discrepancies when measuring the level of liquid with a radar level sensor.
What is the difference between a horn-antenna radar level sensor and a
guided-radar level sensor?
Although they use the same measuring principle, non-contact radar level
sensors, such as horn-antenna radar sensors, and guided-radar level sensors
are different on many points. It is important to know these differences before
selecting which of the two types of sensors you will use for a given application.
The most obvious difference between the two types of radar sensors is the probe
or, for that matter, the absence of probe. Using a probe may improve the
performance of the sensor in some circumstances such as in dusty environment.
A probe also allows interface measurement of two liquids with different dielectric
constants such as oil and water.
Guided-radar level sensors have the disadvantage of being bulky due to the
probe. Also, the level measurement capabilities of such sensors are limited to a
portion of the total length of the probe. As a matter of fact, there is a blocking
distance near the transmitter at the top of the probe and close to the tip of the
probe the precision of the measurement is not guaranteed. This last limitation
prevents the measurement of level below the tip of the probe, hence preventing
to know if a vessel is really empty or if there is a certain amount of substance left
below the probe.
Non-contact radar level sensors, like all non-contact devices, can be used in
harsh environmental condition where it is not desirable that the measured
substance comes in contact with a probe. Since microwaves pass trough plastic
substances, a horn-antenna radar level sensor can even be installed outside a
plastic tank to completely isolate it from the process.
© Festo Didactic 52200-10
5
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Advantages and limitations
Radar level sensors, with or without probe, have several advantages and
limitations. Some of the main advantages of radar level sensors are:

No moving parts, thereby reducing maintenance costs

Not sensitive to temperature or density changes, turbulences, and
vibrations

Available as non-contact sensors

Guided-radar level sensors are suitable for interface measurement

Reliable and accurate

Ability to measure level in very deep tanks, up to 60 meters (200 feet)
However, some limitations are also to be considered:
6

Dependency on the quality of the echo and object inside or outside the
tank, which can cause measurement interference

Dependency on the dielectric constant of the measured substance

Accurate level measurement is impossible close to the mounting flange
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Characteristics of the supplied radar level transmitter
a
This section gives the characteristics of the radar level transmitter, Model
46931. Go directly to the next section on page 10 for the characteristics of the
guided-radar level transmitter, Model 46932.
The radar level transmitter, Model 46931, designed for the Instrumentation and
Process Control System is shown in Figure 4. It consists of a radar level
sensor/transmitter mounted on a flange cap, a remote display with a bracket for
mounting the device on the process workstation, and a cable to connect the
remote display to the transmitter.
Figure 4. Radar level transmitter, Model 46931.
© Festo Didactic 52200-10
7
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Table 1. Components of the radar level transmitter.
 Horn antenna
The radar sensor emits microwaves and detects the
reflected echoes using this antenna.
 Transmitter
The digital transmitter is the computational center and
the main component of this device. It determines the
time of flight of the microwave pulses and calculates
the level from this information.
 Fault panel
Contains one switch used to simulate a fault with the
radar apparatus.
 Ground terminal
The ground terminal is used to connect the device to
ground.
 24 V dc input
Used to energize the radar level transmitter with a
24 V dc signal.
 Electronics
housing
The transmitter’s electronics housing is used to store
the electronic components of the transmitter inside a
protective shelter.
 Remote display
The remote display shows the measured level and
other information related to the operation of the
transmitter. The control keys can be used to manually
set the parameters of the transmitter.
 Display
connection jacks
Connection jacks used to connect the transmitter and
the remote display to each other.
 Remote display
cable
A 20 meters (66 feet) long cable allows connecting the
remote display to the transmitter.
a
The Display connection jack showed by  is connected to the transmitter at
the location shown by . You can clearly see how the Transmitter and the
Remote display are connected with the cable at Figure 10
Remote display keys
The remote display can be used to configure several parameters and to read the
flow rate directly. The function of each button is described below:
Go backwards in a menu or modify a value
Go forward in a menu or modify a value
Select an item from a menu or store an entry
Press the + and – buttons simultaneously to return to
the previous menu or display
8
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Summary of technical specifications
Some of the technical specifications of the radar level transmitter are
summarized in this section. For details, please refer to the manufacturer’s
documentation provided with the device.
Table 2. Technical specifications of the radar level transmitter.
Device name
Measured variable
Power supply
Communication protocols
Operating frequency
Accuracy
Operating temperature of the
sensor
Temperature of the process
Operating pressure of the
sensor
Blocking distance
© Festo Didactic 52200-10
Micropilot FMR51
Level (via time-of-flight)
24 V dc
HART
~26 GHz
±2 mm
-40°C to 80°C
(-40°F to 176°F)
-196°C to 450°C
(-321°F to 842°F)
Vacuum to 16000 kPa
(Vacuum to 2320 psi)
200 mm (7.9 in)
9
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Characteristics of the supplied guided-radar level transmitter
a
This section gives the characteristics of the guided-radar level transmitter,
Model 46932. Go back to the previous section on page 7 for the characteristics
of the radar level transmitter, Model 46931.
The guided-radar level transmitter, Model 46932, designed for the
Instrumentation and Process Control System is shown in Figure 5. It consists of a
radar level sensor/transmitter mounted on a flange cap, a remote display with a
bracket for mounting the device on the process workstation, and a cable to
connect the remote display to the transmitter.
Figure 5. Guided-radar level transmitter, Model 46932.
10
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Table 3. Components of the guided-radar level transmitter.
 Probe
The radar sensor emits microwaves that are guided
along the probe.
 Transmitter
The digital transmitter is the computational center and
the main component of this device. It determines the
time of flight of the microwave pulses and calculates
the level from this information.
 Fault panel
Contains one switch used to simulate a fault with the
radar apparatus.
 Ground terminal
The ground terminal is used to connect the device to
ground.
 24 V dc input
Used to energize the radar level transmitter with a
24 V dc signal.
 Electronics
housing
The transmitter’s electronics housing is used to store
the electronic components of the transmitter inside a
protective shelter.
 Remote display
The remote display shows the measured level and
other information related to the operation of the
transmitter. The control keys can be used to manually
set the parameters of the transmitter.
 Display connection
jacks
Connection jacks used to connect the transmitter and
the remote display to each other.
 Remote display
cable
A 20 meters (66 feet) long cable allows connecting
the remote display to the transmitter.
a
The Display connection jack showed by  is connected to the transmitter at
the location shown by . You can clearly see how the Transmitter and the
Remote display are connected with the cable at Figure 10
Remote display keys
The remote display can be used to configure several parameters and to read the
flow rate directly. The function of each button is described below:
Go backwards in a menu or modify a value
Go forward in a menu or modify a value
Select an item from a menu or store an entry
Press the + and – buttons simultaneously to return to
the previous menu or display
© Festo Didactic 52200-10
11
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Summary of technical specifications
Some of the technical specifications of the guided-radar level transmitter are
summarized in this section. For details, please refer to the manufacturer’s
documentation provided with the device.
Table 4. Technical specifications of the guided-radar level transmitter.
Device name
Measured variable
Power supply
Communication protocols
Operating frequency
Accuracy
Operating temperature of the sensor
Temperature of the process
Operating pressure of the sensor
Probe length
Blocking distance
Levelflex FMP50
Level (via time-offlight)
24 V dc
HART
100 MHz to 1.5 GHz
±2 mm
-40°C to 80°C
(-40°F to 176°F)
-40°C to 80°C
(-40°F to 176°F)
Vacuum to 600 kPa
(Vacuum to 87 psi)
1.03 m (40.6 in)
200 mm (7.9 in)
Installing a radar level transmitter
Installing a radar sensor at the top of the column may require climbing on a
ladder. Always take precautionary measures when using a ladder and wear the
appropriate protective equipment throughout the experiment (safety shoes,
protective eyewear, etc.). In the other case, the installation of a radar transmitter
may require lifting and rotating the water column. In this case, make sure that the
column is empty and that you hold the column when taking off the bolts and nuts.
This operation may require a team to be performed.
A radar level transmitter is pretty straightforward to install. The sensor/transmitter
part of the device must be installed on the flange of the column (the sensor
pointing towards the bottom of the column) and must be properly secured with
bolts and nuts. The remote display is to be installed on the instrumentation
workstation, at a convenient location.
Commissioning a radar level transmitter
The transmitter must be set up for the specific application at hand. The setup for
a typical use on the Instrumentation and Process Control Training System is
explained in the upcoming procedure section. A few important parameters are
nonetheless covered here.
Advanced process conditions
The prevailing conditions in the process column can fluctuate significantly based
on the relative magnitude of the flows, the dimensions of the column, and the
way in which the column is filled (from the top of the column or from the bottom).
12
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
As a result, the surface of the liquid can vary from very turbulent to still and the
level can change quickly or slowly, in a uniform way or not.
This wide spectrum of possibilities makes it difficult for the sensor to measure
and display a precise level at an adequate rate. A balanced choice must be
made between the stability and reliability of the measured value and the reaction
time of the sensor. A slowly-varying level with a calm surface would be best
measured if the sensor averaged its readings over a relatively long period of
time. On the other hand, a quickly changing level may need to be monitored with
a much shorter averaging time (e.g. to avoid an overflow), even if it must be done
at the expense of some precision.
The transmitter offers a series of preset options for different applications, each
with different parameters for the time-averaging filter and for the input-stabilizing
filter. The most useful one is usually the Small tanks (< 1m/3ft) setting, since the
process column (46901) is qualified as a small tank (relative to industrial tanks).
Small tanks have levels that are likely to change quickly. Thus, they provide short
reaction times. The options which are likely to be used are presented below. You
are encouraged to test them and determine which ones give the best results in
different situations.
Table 5. Summary of the main advanced process conditions options.
Advanced process
conditions
Applications
Settings
Foam
(>5cm/0,16ft)
This option makes sure that no
tank history is used which has
been recorded while foam was
present at the surface and thus
is no reliable map of the tank
property.
Evaluation mode = Long time
history is deactivated.
Changing DC
values
A tank history which has been
recorded and is only valid for a
fixed dielectric constant. The
Changing DC values option
avoids measuring values in the
case of a changing dielectric
constant.
Evaluation mode = Long time
history is valid for a fixed
dielectric constant.
Small tanks
(< 1m/3ft)
This option provides a simple
possibility to reduce the echo
width of the sensor module.
This enables an improved
detection of superimposed
echos - especially in the near
field. Internally, all parameters
related to the echo width are
adjusted by this option.
Only available for liquid
measurements with 26 GHz HF
module.
None
Reset of the transmitter
Radar level transmitters can be reset anytime you want to work with a clean
configuration. Doing so restores the parameters to default values and deactivates
linearization and interference echo settings. Keep in mind that a setup procedure
like the one described below is always required after a reset.
© Festo Didactic 52200-10
13
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Linearization
Radar transmitters offer the option of converting a measured level into another
quantity (such as a volume, a mass, a percentage, etc.) according to one of
many preset functions or according to a linearization table. As the process
column has a regular cylindrical shape, only the linear type will be used (refer to
the device documentation for information about the other types, if required).
The linear type needs three parameters:

The portion of the tank you want to linearize (the filled part or the part
above the level) and the type of unit (technical unit (CD) or distance unit
(DU)).

The unit you want to use (m3, ft3, L, kg, lbs)

The maximal value (in the specified unit) for a 100% level. This
linearization type assumes that the minimal value is 0 (in the specified
unit) for a 0% level.
Echo envelope curve
Waves propagating in non-ideal conditions are likely to rebound on obstacles and
eventually return to the sensor. The problem is that it takes such unwanted
echoes a different time to go back to the sensor than it would normally take to hit
the surface of the liquid and go back to the sensor in a straight line. This causes
the detection of unwanted signals, unrelated to the actual level in the column,
and skews the results. Thankfully, those unwanted echoes can be expected to be
present with the same strength for a certain level of liquid every time an echo
pulse is sent. Consequently, a background picture of parasitic echoes in an
empty column can be recorded and looks as shown on Figure 6.
Echo Envelope Curve
Figure 6. Envelope curve for an empty column.
The echo envelope curve is a recording of the relative intensity of returning
electromagnetic waves as a function of the distance traveled by the waves before
being reflected. An echo envelope curve gives a broad picture of all the signals
measured by a sensor for a given level of liquid in the column.
Once the envelope curve of the empty vessel is known, it is straightforward to
determine a filter mapping which will ignore any echo signals which are not
stronger than the typical background echo noise. Doing so ensures that only
relevant signals are considered, thus improving the reliability of the level
measurement. A mapping computed automatically by the transmitter is shown in
14
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Discussion
Figure 7. Note that it is a curve slightly above but following closely the echo
envelope curve in the range in which it is defined.
Mapping
Figure 7. An appropriate mapping (in black) for the envelope curve.
If you change or modify the vessel in any way that affects the propagation of the
microwaves (by adding an obstacle or a probe for instance), it is strongly
recommended that a new envelope curve be recorded and a new corresponding
filter mapping be produced. It is important to limit the range of the mapping so as
to be a few centimeters (about an inch) short of the column baffle plate. This
avoids filtering out the echo signaling that the level is at its minimum.
When a certain level of liquid is present in the column, the path of the
microwaves pulses is altered. This results in a modified envelope curve with
respect to the one of the empty column. To determine the level, the transmitter
ignores the signals whose strength is below the mapping curve and identifies the
first peak above the mapping curve as the correct signal (Figure 8).
Echo Peak
Blocking distance
Figure 8. Determining the distance between the detector and the surface of the liquid.
Correction offset
It is possible to adjust the displayed value as measured by the radar level
transmitter if you find out after a comparison with the value given by a ruler or
another measuring device that it is off by a constant.
© Festo Didactic 52200-10
15
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure Outline
PROCEDURE OUTLINE
The Procedure is divided into the following sections:





Set up and connections Commissioning the level transmitter Adding an offset Displaying level in percentage of span How to obtain a volume reading 
Making a new mapping Calculating the max. scale parameter.
Making a new mapping with the radar level transmitter. Making a new
mapping with the guided-radar level transmitter.
PROCEDURE
Set up and connections
a
Throughout this procedure the expression “radar level transmitter” or
“transmitter” stand for either the transmitter Model 46931 or 46932, which ever
you use.
1. Connect the equipment according to the piping and instrumentation
diagram (P&ID) shown in Figure 9 and use Figure 10 to position the
equipment correctly on the frame of the training system. To set up your
system for this exercise, start with the basic setup presented in the
Familiarization with the Instrumentation and Process Control Training System
manual and add the equipment listed in Table 6.
2. Radar level sensors use electromagnetic waves to detect the level of water in
a vessel. This has several advantages. However, in the case of a nonmetallic tank, such as the column used in the current exercise, the
electromagnetic waves emitted by the transmitter are not confined to the
vessel. Like light, they can go through the column. Hence, the
electromagnetic waves can also be reflected by objects around the column.
To minimize the risk of level reading errors due to interferences from objects
outside the column, try to remove from the process station any unused struts
or devices close to the column.
16
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
Table 6. Material to add to the basic setup for this exercise.
Name
Radar level transmitter
or
Guided-radar level transmitter
Electrical unit
Model
46931
or
46932
46970
Pneumatic unit
46971
Accessories
46993
Identification
LIT 1
Radar
Vent
tube
Figure 9. P&ID.
© Festo Didactic 52200-10
17
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
Figure 10. Setup.
3. Connect the control valve to the pneumatic unit. Details about the installation
and operation of the control valve are available in the Familiarization with the
Instrumentation and Process Control Training System manual.
4. Connect the pneumatic unit to a dry-air source with an output pressure of at
least 700 kPa (100 psi).
18
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
5. Wire the emergency push-button so that you can cut power in case of
emergency. The Familiarization with the Instrumentation and Process Control
Training System manual covers the security issues related to the use of
electricity with the system as well as the wiring of the emergency pushbutton.
6. Do not power up the instrumentation workstation yet. You should not turn the
electrical panel on before your instructor has validated your setup—that is
not before step 12.
7. If a flange top is already in place on the process column, unbolt and carefully
remove this component from the column. Place the sensor/transmitter part of
the radar level transmitter on top of the flange, the sensor pointing
downwards into the column. Bolt the transmitter flange in place.
Installing a radar sensor at the top of the column may require climbing on a
ladder. Always take precautionary measures when using a ladder and wear the
appropriate protective equipment throughout the experiment (safety shoes,
protective eyewear, etc.). In the other case, the installation of a radar transmitter
may require lifting and rotating the water column. In this case, make sure that the
column is empty and that you hold the column when taking off the bolts and nuts.
This operation may require a team to be performed.
8. Install the remote display at a convenient location on the process
workstation. Connect the remote display cable to the connection jacks on the
transmitter and on the display.
9. Connect the transmitter to a 24 V dc power outlet on the electrical unit. Use
one of the direct outputs to keep the transmitter from shutting off in case the
emergency push-button or the OFF button (S1) is used.
10. Before proceeding further, complete the following checklist to make sure you
have set up the system properly. The points on this checklist are crucial
elements to the proper completion of this exercise. This checklist is not
exhaustive, so be sure to follow the instructions in the Familiarization with the
Instrumentation and Process Control Training System manual as well.
f
 All unused male adapters on the column are capped and the flange is
properly tightened.
 The ball valves are in the positions shown in the P&ID.
 The valve at the suction of the pump (HV1) is set the open position, so that
the flow is directed toward the pump inlet.
 The control valve is fully open.
 The pneumatic connections are correct.
© Festo Didactic 52200-10
19
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
11. Ask your instructor to check and approve your setup.
12. Make sure it is safe to energize the system for you and for the team working
on the other side of the system, if any. When ready, turn on the main power
by pushing the handle of the safety switch in the ON position. Do not press
the S2 button yet.
The transmitter initializes and the remote display turns on after 30 seconds or
even more. This happens because the device is explosion proof.
Commissioning the level transmitter
a
The following procedure assumes you are using the remote display to program
the transmitter. If you want to configure your transmitter from a computer, you
can do so by accessing the same menus and inputting the same values in the
appropriate fields of the FieldCare software, or the DeviceCare software.
Please refer to the HART Software Configuration student manual (P/N 86050)
for more information on how to connect your transmitter to a computer.
Appendix A, Appendix B, Appendix C, and Appendix D give an overview of
how to configure the radar level transmitter and the guided-radar level
transmitter using FieldCare and DeviceCare.
13. It is recommended that you reset the device in order to start with the factory
settings. To do this, press the E button from the main display to access the
Micropilot 5x menu. Use the + and – buttons to select the Setup group and
then press the E button to access the Setup function group. Next, press the +
and – buttons to access the Advanced setup group. Once again, use the +
and – buttons to reach the Administration group and press the E button. On
the Device reset field, select To factory defaults using the + and – buttons.
Press E to complete the reset.
(i.e., the + and – buttons simultaneously) a few times to return to
14. Press
the Micropilot 5x menu.
15. The first thing you may want to configure on the transmitter is the type of unit
used to indicate the level (%, m, ft, mm, or inch). From the Micropilot 5x
menu, select the Setup menu group and press the E button. Using the +
and – buttons, go to the Advanced setup menu and press the E button. Then
proceed the same way to reach the Level sub-menu. Once there, press
the E button and reach the Level unit field using the + and – buttons. Once
there, select between %, inch, m, ft, and mm. Press E to confirm your choice
to return to the Micropilot 5x menu.
and use
16. The transmitter can either display the level of liquid using the unit selected in
the Level unit function or using the technical unit of your choice: %, unit of
length, volume, or mass. How to display the volume or mass of liquid in the
column is detailed later in this exercise. For the moment, we will use the unit
selected at step 15.
20
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
17. To do so, select the Linearization function group on the Advanced setup subto
menu and, in the Linearization type function, select Linear and use
return to the Setup function, where the level value is displayed. The
measured value should be in the unit set in the Level unit function. However,
it is probably erroneous since the parameters ensuring the correct operation
of the transmitter have not been set yet.
18. Go to the Expert menu using the + and – buttons and type 0000 in the
Access code field. Press E to confirm. Then select the Sensor function menu
and reach the Level sub-menu. In the Output mode field, make sure that
Level linearized is chosen.
19. Depending on the unit you have selected, you may have to change the
number of decimals displayed by the transmitter in order to obtain the
desired precision. To do so, go to Setup  Advanced setup  Display. As
you can see, the transmitter can display different types of values (Level
linearized, Distance, Current output 1, Measured current, Terminal voltage,
Electronic temperature, Analog output adv. diagnostics). These can be
selected in the Value display fields. For each type of value, you can set the
desired number of decimals in the decimal places field. Each Value display
field has its related decimal places field, and they are identified by the same
corresponding number. For now, we only use the Value 1 display field (set to
Level linearized) and the decimal places 1 field.
The other options available
in the linearization function
are described and tested
from step 38 to step 45 of
this exercise.
20. You must give information on the process to the transmitter so that it reads
the level correctly. This information includes, among other things, the type of
tank, the dielectric constant of the liquid or solid in the tank, the process
conditions, the probe characteristics, the empty calibration value, the full
calibration value, and the mapping information. You can provide all this
information to the transmitter via the Setup function group.
Set the parameters in the Setup function group as shown in Table 7 for the
radar level transmitter, Model 46931, or as in Table 8 for the guided-radar
level transmitter, Model 46932.
© Festo Didactic 52200-10
21
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
Table 7. Setting for the level radar transmitter, Model 46931.
Function
Setting
Path
Description
Tank shape
Bypass/pipe
Setup -> Tank type
This is the type of tank proposed by
the manufacturer.
Medium group
Water based
(DC>=4)
Setup -> Medium group
Specifies the dielectric constant of
the medium and presets the
medium property parameter.
Empty calibr.
1.070 m (42 in)
Setup -> Empty calibr.
Distance between the mounting
flange and the minimum level (0%).
Full calibr.
0.750 m (29 in)
Setup -> Full calibr.
Distance between the minimum
(0%) and the maximum level
(100%).
Confirm distance
Manual map
Setup -> Confirm distance
The range of mapping is to be
defined manually.
Mapping end point
0.76 m (30 in)
Setup -> Map. End point.
The range of mapping for the radar
level transmitter must not be below
the baffle plate at the bottom of the
column.
Medium type
Liquid
Setup -> Advanced -> Level ->
Medium type
Indicates if the measured substance
is a solid or a liquid.
Medium property
DC 4 ... 7
Setup -> Advanced setup ->
Level -> Medium property
Dielectric constant of the measured
medium.
Process property
Standard < 1 m (40
in) /min
Setup -> Advanced setup ->
Level -> Process property
This is the most convenient mode.
Advanced process
conditions
Small tanks (1m/3ft)
Setup -> Advanced setup ->
Level -> Advanced process
condition
This is the most convenient mode
for the process column (46901).
Blocking distance
0.2 m
Setup -> Advanced setup ->
Level -> Blocking distance
Mentioned above, in the Discussion
section.
22
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
Table 8. Setting for the guided-radar level transmitter, Model 46932.
Function
Setting
Path
Description
Tank type
Bypass/pipe
Setup -> Tank type
Even though the column is non
metallic, this setting also works
relatively well because of the
metallic baffle plate installed at the
bottom of the column.
Medium group
Water based (DC >
= 4)
Setup -> Medium group
Dielectric constant of the measured
medium.
Empty calibration
1.070 m (42 in)
Setup -> Empty calibration
This is the most convenient mode.
Different modes can also be used.
Full calibr.
0.740 m (29 in)
Setup -> Full calibration
Distance between the minimum
(0%) and the maximum level
(100%).
Confirm distance
Manual map
Setup -> Confirm distance
This setup is used since the range
of mapping will be entered
manually.
Mapping end point
1.03 m (42 in)
Setup -> Mapping end point
Since the mapping is done with an
empty column, it is recommended
to use a range of mapping equal to
the probe length.
Medium type
Liquid
Setup -> Advanced setup ->
Level -> Medium type
Indicates if the measured substance
is a solid or a liquid.
Medium property
DC 4 ... 7
Setup -> Advanced setup ->
Level -> Medium property
Dielectric constant of the measured
medium.
Process property
Standard < 1m (40
in) /min
Setup -> Advanced setup ->
Level -> Process property
This is the most convenient mode.
Blocking distance
0.2 m
Setup -> Advanced setup ->
Level -> Blocking distance
Mentioned above, in the Discussion
section.
Probe grounded
No
Setup -> Advanced setup ->
Probe settings -> Probe
grounded
The probe is not grounded.
Probe length
1.03 m (42 in)
Setup -> Advanced setup ->
Probe settings -> Probe length
The probe length is measured from
the flange to the tip of the probe.
Setup -> Advanced setup ->
Probe settings -> Confirm probe
length
The transmitter can determine the
length of uncovered probes
automatically. This is not necessary
since the length of the probe has
been provided to the transmitter
(see probe length above).
Confirm probe
length
Probe length ok
21. Press the S2 button to power all the devices not already active on the station
(i.e., the drive, the pneumatic devices, etc.) and make sure the S1 button is
set to the ON position.
22. Test your system for leaks. Use the drive to make the pump run at low speed
to produce a small flow rate. Gradually increase the flow rate, up to 50% of
the maximum flow rate that the pumping unit can deliver (i.e., set the drive
speed to 30 Hz). Repair any leaks.
© Festo Didactic 52200-10
23
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
23. Fill the column with water up to a level of about 0.80 m (31 in) on the ruler.
24. Stop the pump and close HV2 and HV4.
25. Use HV4 to adjust the level of water until you read 0.75 m (29 in) on the
radar level transmitter display. Write below the level of water indicated on the
ruler.
About 0.717 m (27.7 in) using the radar level transmitter, Model 46931. The
results may differ depending of you setup or the type of transmitter you use.
26. Use HV4 to adjust the level of water until you read 0.001 m (0.1 in) on the
transmitter display. Write below the level of water indicated on the ruler.
About 0.04 m (1.5 in).
27. Explain why the level on the ruler does not correspond to the level on the
display of the transmitter.
The zero of the ruler does not correspond to the zero entered in the basic
setup function of the radar level transmitter. An offset must be added to the
setting of the transmitter so that the two zeros match.
28. If you experience problems while trying to measure the maximum and
minimum levels configured on the transmitter, your setup may require fine
tuning of some of the transmitter parameters such as the mapping. You may
go to the Making a new mapping section immediately to perfect your
mastering of the transmitter mapping function and come back later to
complete the rest of the exercise once you have fine tuned your transmitter.
Tuning a radar level transmitter is not an easy task and it requires a little bit
of practice and a sound understanding of the mapping process. Be aware
that you may also need to change some of the parameters entered in the
Setup function to fit the tuning of your transmitter to yours needs or to adapt
it to some particularities of your setup.
Adding an offset
29. Fill the column again and close HV4 and HV2.
24
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
The results may vary depending if you are using the
transmitter Model 46931 or
46932. The characteristics
of these two transmitters
differ slightly, especially at
the top and bottom of the
range.
30. Use HV4 to decrease the level of water in the column by steps of 5 cm (2 in).
Fill Table 9 with the results. Also, calculate the difference between the level
on the ruler and the level on the transmitter (∆Level).
Table 9. Measurement of the level (ruler vs. radar level transmitter).
Level on the ruler
cm (in)
Level on the transmitter
cm (in)
∆Level
cm (in)
80 (31)
The results are presented below.
Measurement of the level in centimeters.
Level on the ruler
(cm)
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
© Festo Didactic 52200-10
Level on the transmitter
(cm)
75.4
71.6
66.9
61.8
57.1
52.0
47.3
42.2
36.6
31.6
26.4
21.1
15.8
16.3
7.4
1.6
0.0
∆Level
(cm)
4.6
3.4
3.1
3.2
2.9
3
2.7
2.8
3.4
3.4
3.6
3.9
4.2
-1.3
2.6
3.4
0.0
25
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
Measurement of the level in inches.
Level on the ruler
(in)
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
0
Level on the transmitter
(in)
29.6
27.7
25.7
23.8
21.7
19.8
17.8
15.8
13.7
11.6
9.5
7.5
5.8
4.7
1.8
0.0
0.0
∆Level
(in)
1.4
1.3
1.3
1.2
1.3
1.2
1.2
1.2
1.3
1.4
1.5
1.5
1.2
0.3
1.2
1.0
0.0
31. You may have noted that ∆Level is relatively constant except for extreme
values (i.e., at the top of the span or at the bottom of the span). Therefore,
we can approximate that the offset between the level on the ruler and the
level measured by the transmitter is constant.
For some applications, it may be convenient to match the level the
transmitter displays with the level read on the column ruler. To do this, we
will use the mean value of ∆Level for levels in the middle of the span.
32. First, calculate the mean value of ∆Level for levels on the ruler
between 0.70 m and 0.20 m (27 in and 7 in).
Approximately 3.3 cm (1.3 in).
33. Go to the Expert menu. Enter 0000 in the Access code field if required. Then
go to the Sensor function group and select the Level sub-menu.
34. In the Level correction field, enter the value calculated at step 32.
35. Fill the column again and close HV4 and HV2.
26
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
36. Use HV4 to decrease the level of water in the column by steps of 5 cm (2 in).
Fill Table 10 with the results. Also, calculate the difference between the level
on the ruler and the level on the transmitter (∆Level).
a
To switch between SI units and U.S. customary units, go to Advanced setup 
Level.
Table 10. Measurement of the level (ruler vs. radar level transmitter).
Level on the ruler
cm (in)
Level on the transmitter
cm (in)
∆Level
cm (in)
80 (31)
© Festo Didactic 52200-10
27
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
The results are presented below.
Measurement of the level in centimeters.
Level on the ruler
(cm)
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Level on the transmitter
(cm)
79.1
75.0
70.2
65.1
60.6
55.2
50.6
45.4
40.1
34.9
29.7
24.6
19.9
19.1
10.0
4.8
0.0
∆Level
(cm)
0.9
0
-0.2
-0.1
-0.6
-0.2
-0.6
-0.4
-0.1
0.1
0.3
0.4
0.1
-4.1
0.0
0.2
0.0
Measurement of the level in inches.
Level on the ruler
(in)
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
0
Level on the transmitter
(in)
31.0
29.0
27.1
25.1
23.1
21.1
19.0
17.0
15.1
13.0
11.1
8.9
7.3
5.9
3.1
1.4
1.4
∆Level
(in)
0
0
-0.1
-0.1
-0.1
-0.1
0
0
-0.1
0
-0.1
0.1
-0.3
-0.9
-0.1
-0.4
-1.4
37. If there is still an important offset, correct the problem by adjusting the value
of the offset function.
28
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
Displaying level in percentage of span
38. The transmitter can also display the level in percentage of the span or in
other measuring unit. Switch to a level measured in percentage. To do so,
use Table 11 to configure the display of the level in percentage.
Table 11. Settings for reading the level in percentage of span.
Path
Parameter
Value
Setup -> Advanced setup -> Level
Level unit
%
Setup -> Advanced setup -> Linearization
Linearization type
Linear
Setup -> Advanced setup -> Linearization
Unit after
linearization
%
Setup -> Advanced setup -> Linearization
Maximum value
100%
39. The transmitter should now display the measured level in percentage of the
span.
40. Fill the column again and close HV4 and HV2.
41. Use HV4 to decrease the level of water in the column by steps of 5 cm (2 in).
Fill Table 12 with the results.
Table 12. Measurement of the level (ruler vs. radar level transmitter).
Level on the ruler
cm (in)
Level on the transmitter
%
80 (31)
© Festo Didactic 52200-10
29
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
The results are presented below.
Measurement of the level in centimeters on the ruler.
Level on the ruler
(cm)
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
Level on the transmitter
(%)
105.0
99.8
93.6
86.7
80.6
73.6
67.5
60.3
53.5
46.4
39.5
32.3
25.3
22.4
15.1
6.3
4.4
Measurement of the level in inches on the ruler.
Level on the ruler
(in)
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
1
0
30
Level on the transmitter
(%)
107.5
100.2
93.5
87.1
79.8
73.3
66.5
59.1
52.0
44.7
37.6
30.5
25.6
20.4
10.5
5.2
5.2
© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
42. Is the agreement satisfactory?
 Yes
 No
Yes
How to obtain a volume reading
The radar level transmitter cannot directly measure the volume of liquid in a tank.
However, given some information, it can infer the volume occupied by the liquid.
To correctly infer the volume of water in the column, the transmitter needs the
volume of liquid in the column when the level is at 100%. This volume is the max.
scale volume. Below is an example of how to calculate the maximum scale
volume so that the transmitter displays a volume of 0 L (0 gal) when the
transmitter measure a level of 0% and a volume corresponding to the maximum
scale volume when the transmitter measure a level of 100%. Figure 11 shows
the portion of the total volume of liquid in a vessel that is measured by the radar
level transmitter using this method.
Measured portion of
the liquid measured
by the sensor
The liquid below
0% is not taken into
account by the
transmitter
Figure 11. Portion of the total volume of liquid in a vessel measured by the radar transmitter.
Calculating the max. scale parameter
The volume of a cylinder can be calculated using Equation (3).
(3)
where
is the radius of the cylinder
is the height of the cylinder
The process column has an inner diameter of 0.203 m (8 in) and you have set
before the value of the full calibr. parameter to 0.740 m (29 in).
© Festo Didactic 52200-10
31
Exercise 1 – Fundamentals of Radar Level Transmitters  Procedure
Using these values and Equation (3), you can calculate the full calibr. parameter.
Below is the calculation of the full calibr. parameter to display the volume in liters
or in gallons:
max. scale
max. scale
0.203
2
∙
∙
8
2
∙ 0.740 ∙ 1000
∙ 29 ∙ 0.004329
24 6.31
43. Use Table 13 to set the transmitter to display the volume of water in the
column.
Table 13. Setting the transmitter to display the volume of water.
Path
Parameter
Value
Setup -> Advanced setup -> Linearization
Linearization type
Linear
Setup -> Advanced setup -> Linearization
Unit after
linearization
L or gal
Setup -> Advanced setup -> Linearization
Maximum value
24 l or 6.31 gal
44. The transmitter displays the volume of water in the column in the desired
unit. With this setting, the volume of water in the column is 0 L (0 gal) at 0%
of the span and 24 L (6.31 gal) at 100% of the span.
45. Fill the column with water and verify that at 100% of the span, the transmitter
displays a volume of 24 L (6.31 gal) and that at 0% of the span, it displays a
volume of 0 L (0 gal).
Making a new mapping
As detailed in the discussion section, adding a mapping to the setup of the
transmitter may help to get rid of unwanted echo signals. Sometimes, mapping
the column all the way to the bottom is not the best way to proceed. Moreover,
for vessels without objects interfering with the transmitter signal, using a mapping
may be more a nuisance than an advantage. This section explains how to delete
an existing mapping and make a new one. To perfect your knowledge of
mapping, it is recommended that you try different mapping distances, observe
the resulting mapping curves, and try to understand how mapping works.
Before recording a new mapping it is essential to erase the existing mapping
when the option is available. The procedure to make a new mapping differs
slightly depending if you are using a radar level transmitter or a guided-radar
level transmitter. Both procedures are resumed below.
Making a new mapping with the radar level transmitter
46. To proceed to the mapping, select manual map from the Confirm distance
field in the Setup menu.
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© Festo Didactic 52200-10
Exercise 1 – Fundamentals of Radar Level Transmitters  Conclusion
47. Using Table 14, set the mapping with the suggested parameters.
Table 14. Mapping setting for model 46931.
Function
Setting
Confirm distance
Manual map
Mapping end point
0.76 m (30 in)
Start mapping
On
Making a new mapping with the guided-radar level transmitter
48. To erase the existing mapping, select delete map from the Confirm distance
field in the Setup menu.
a
This option is not available for the radar level transmitter.
49. To proceed to the mapping, select manual map from the Confirm distance
field in the Setup menu.
50. Using Table 15, set the mapping with the suggested parameters.
Table 15. Mapping setting for model 46932.
Function
Setting
Confirm distance
Manual map
Mapping end point
1.03 m (43 in)
Record map
Yes
CONCLUSION
In this exercise you have learned how to commission a radar level transmitter for
use on Instrumentation and Process Control system. You learned the principles
of echo detection and the use of a filter mapping.
REVIEW QUESTIONS
1. Describe briefly the principle of operation of a radar level sensor.
A radar level sensor emits wave packets of microwaves and infers the level
from the time it takes for the wave packets to bounce on the surface of the
fluid (or solid) and return to the sensor. This method is called the time-offlight method.
2. Which of the horn-antenna radar level transmitter or the guided-radar level
transmitter is more suitable when the measured substance is corrosive?
Horn-antenna radar level transmitter
© Festo Didactic 52200-10
33
Exercise 1 – Fundamentals of Radar Level Transmitters  Review Questions
3. Give one advantage and one disadvantage of radar level transmitters:
Many answers are possible. Here are a few suggestions:
Advantages

They have no moving parts, which reduces the maintenance costs

They are not sensitive to temperature or density changes,
turbulences, and vibrations

They are available as non-contact sensors

Guided-radar level sensors are suitable for interface measurement

They are reliable and accurate

They can measure level in very deep tanks, up to 60 meters
(200 feet)
Disadvantages

Radar level sensors depend on the quality of the echo and object
inside or outside the tank may interfere with the measurement

They depend on the dielectric constant of the measured substance

Close to the mounting flange, the sensor cannot measure the level
accurately or at all
4. What is an echo envelope curve?
The echo envelope curve is a recording of the relative intensity of the
microwaves returning to the emitter as a function of the distance traveled by
the microwaves before being reflected.
5. What is the mapping and what effects does it have on the measurement of
the level inside a vessel?
The mapping is a curve approximating the echo envelope curve (usually for
an empty vessel) but slightly above it. It acts as a filter which ignores any
signal weaker than the mapping when determining the echo peak, thus
avoiding known obstacles and improving the reliability of the measurements.
34
© Festo Didactic 52200-10
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