2 Radar Basic

SaabRosemount Tank Radar AB - Tank Gauging Divison - Training course April 7, 2023 1

Radar TechnologyRadar TechnologyMicrowaves


Other Non-contacting TechniquesOther Non-contacting Techniques Ultrasonic Measurement with sound

Devices are affected by: Tank temperature Tank pressure.

Light Measurement with laser Devices are affected by:

Product vapor Dirt/deposits on lens Laser doesn’t work on some kind of oils ( lubricant oil)


What is radar?What is radar? Frequency of 1-60 GHZ

Wavelength of 0.5-30 centimeters

Wavelength = speed of light / frequency

The speed of light is 3*10^8 m/s in air

The speed varies depending on the medium


Why Radar?Why Radar?

Radar level devices are

Not Heat sensitive

Not Dust/moisture sensitive

Not affected by pressure


The spectrumThe spectrum


About Radar RadiationAbout Radar Radiation Is Radar radiation dangerous?

Depends upon power output.

Radar radiation transmitted from radar transmitter is NOT !

You can safely stand under a transmitter without any health concerns.

A cell phone sends out 3000 times more radiation, even the sun sends out more microwave radiation!


Different Types of RadarDifferent Types of Radar Saab Rosemount manufactures two different types of radars

FMCW type REX and PRO/5600

Pulse Type 3300 and 5400

PULSE

FMCW


Pulse Radar Measure Pulse Radar Measure

How does a radar measure level

The radar sends out a signal

Reflected by the product surface

The signal returns to the radar

The distance can be calculated by:

Distance=(speed x time*)/2


Pulse radarsPulse radarsThe pulse radar sends out a pulse and measures the time it takes for the pulse to return.

Difficulties…

Inaccurate way of measuring time…

10 meter distance is equal to 66.6 ns (0.000 000 066 sec)


FMCW radarsFMCW radarsThe FMCW technology uses a continuous transmission that varies in frequency.

d

Time t

f ~ d

10

9

t0

f

Frequency f (GHz)


Block diagram:Target

VCOPower splitter

Mixer

fVCO

fVCO - fref

fref

A FMCW radar compares the received signal with the transmitted. By continuously changing the transmitted frequency there will be a difference between the received and transmitted signal. This difference is proportional to the distance to the liquid.

FMCW - Principle of Operation 1FMCW - Principle of Operation 1


0 50 100 150 200 250 300 350 400 4509.4

9.6

9.8

10

10.2

10.4

Frequency (GHz)

0 10 20 30 40 50 60 70 80 90 100 110

1

0

1

v( )t

Time (ms)

Time (ms)

Frequency domain

Time domain

FMCW - Principle of Operation 2FMCW - Principle of Operation 2


Pulse radars – equivalent time samplingPulse radars – equivalent time sampling

Real Time in nS

Sampling Clock in uS

Equivalent Waveform in mS

Technique is used in Digital Sampling Oscilloscopes


AntennasAntennasThe antenna is a very important part of the transmitter, since it affects the measuring range and the beam width.

“The larger the antenna, the better the performance” is a good rule.

Antenna footprint is oval for a circular antenna(horn, parabola etc.)

Tank wall

Footprint


AntennasAntennasAntennas should be designed so that product build-up and condensation deposits are avoided.

Saab patent

Saab patent


Different frequencies – scatteringDifferent frequencies – scattering

6 GHz 26 GHz


Different frequencies – beam angleDifferent frequencies – beam angle

Wall reflection

6 GHz 26 GHz


Different frequenciesDifferent frequenciesA higher frequency gives a more concentrated beam, but is also more sensitive to contamination and scattering.

Contamination and scattering sensitivityBeam angle

Frequency(GHz)

Frequency(GHz)

5 26 5 26(log)(log)


Saab Rosemount frequencySaab Rosemount frequency

The Saab Rosemount gauges use a frequency of 10 GHz.

Frequency (GHz)5 2610(log)


Permittivity and dielectric constantPermittivity and dielectric constant Dielectric constant (relative permittivity)

defines how well the radar waves interact with the product.

Some of the radar wave energy reflects off the surface, and some of the energy continues through the product.

High dielectric constant reflects a lot

Low dielectric constant reflects little


High and low dielectric constantHigh and low dielectric constant

Reflection from water (εr=80) Reflection from oil (εr=2)


Disturbance echoesDisturbance echoes Disturbance echo = an echo that is not coming from the

level Can originate from:

Nozzle edges Heating coils Agitator blades Pipe deposits Ladders

Disturbing echoes will consume energy from the measurement

Disturbing echoes close to the surface may cause inaccuracies


The speed of lightThe speed of light Speed of light

not constant

depends on the material

The higher the dielectric constant, the slower the radar waves travel

low dielectric application with flat tank bottom

interface application


Flat tank bottomFlat tank bottom

tank signal

x√εr * x

εr = 2


Interface applicationInterface application

tank signal

x√εr * x


PolarizationPolarizationLinear polarization = The electric field is always in the same direction - it does not turn.

Looking from the side Looking into the wave


PolarizationPolarizationObjects which are oriented in the same direction as the electric component interfere more than the objects that are oriented perpendicular to the electric vector.

LPG Operation mode- small pin echo

LPG Test mode- big pin echo


PolarizationPolarization

from gauge

reflected

from gauge

reflected

The restricted movement of the electrons accounts for the small reflection


Microwave modes in still pipesMicrowave modes in still pipesThe TE01 mode has an electrical field which does not touch the pipe walls, and almost no energy at all is lost in the rust and deposits on the pipe wall.

Low Loss Mode(Saab patent)3940 & 3950

Standard ModeAll other antennas

Sensitivity to adhesion 0.005%

Sensitivity to adhesion 0.6%

2 Radar Basic

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