Radar and Ultrasonic Level Measurement

8/7/2019 Radar and Ultrasonic Level Measurement

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Level Measurement with Radar and Ultrasonic

NorCal Tech 2005 Technical Conference

Level Measurement with Radar and

Ultrasonic




Technologies

Through Air

Radar

Guided Wave

Radar

Ultrasonic




How it works

The time it takes for the instrument¶s

signal to leave the antenna, travel to the

product, and return to the antenna is

calculated into distance.

The instrument is spanned according tothe distance the 100% and 0% points

within the vessel are from its reference

point .

The measured distance can then be

converted into the end user¶s desired

engineering unit and viewed on the head

of the instrument or remote display.

100%100%

0%0%




How do process conditions affect the

reliability and accuracy of process

level transmitters ?

density (specific gravity)?

dielectric constant?

conductivity?

temperature?

pressure?

vacuum?

agitation?

vapors and condensation?

dust and build up?

internal structures?

Process conditions that affect specification of transmitters




Through Air

Radar




Radar Technology ± How it works

Radar is a time of flight measurement.

Microwave energy is transmitted by theradar.

The microwave energy is reflected off the product surface

The radar sensor receives themicrowave energy.

The time from transmitting to receivingthe microwave energy is measured.

The time is converted to a distancemeasurement and then eventually alevel.




Function of an antenna

Signal focusing

� reduction of the antenna ringing

� optimization of the beam

Signal amplification

� focusing of the emitted signal

� amplification of the receipt signal

Signal orientation

� point at the product surface

� minimization of false echoreflections




Radar level measurement

Top mounted

Solids and liquids applications

Non-contact

RADAR is virtually unaffected by the

following process conditions:

Temperature

Pressure and Vacuum

Conductivity

Dielectric Constant (dK)

Specific Gravity

Vapor, Steam, Dust or Air Movement

Build up (depends on radar design)

Radar Technology ± Why use it?




Radar Technology - Choice of frequency

Radar wavelength = Speed of light / frequency

P = c / f

Frequency 6.3 GHz

wavelength P= 47.5 mm

Frequency 26 GHz

wavelength P= 11.5 mm

High frequency:

shorter wavelength

narrower beam angle

more focused signal

ability to measure smaller vessels

with more flexible mounting

47.5mm47.5mm

11.5mm11.5mm

Low frequency:

longer wavelength

wider beam angle

less focused signal

ability to measure in vessels with

difficult application variables




5 GHz 10 GHzFrequency

Comparison of horn diameters that produce the same beam angle

20 GHz15 GHz 25 GHz

Focusing at 6.3 GHz:

Horn size Beam angle

3³ 38°

4³ 33°

66" 2121°°

10³ 15°

Focusing at 26 GHz:

Horn size Beam angle

1.51.5" 2222°°

2³ 18°

3³ 10°

4³ 8°

Radar Technology ± Focusing of Frequency

30 GHz

6.3 GHz6.3 GHz 26 GHz26 GHz

(A shorter wavelength means a smaller antenna for the same beam angle)




Major Factors in Specifying a Radar - Frequency

Frequency

Choosing a frequency depends on:

Mounting options

Customer¶s 100% point

Vessel dimensions ± proximity

of connection to sidewall

The presence of foam

Agitated product surfaces

Vapor composition

Vessel internal structures Dielectric constant (dK)




Radar Technology ± Choosing a frequency

Low Frequency ± 6.3 GHz ± C-band

Better Performance with:

Heavy Agitation Severe Build-up Foam Steam Dust

Mist Dish bottom vessels

Typical accuracy: +/- 10mm

High Frequency ± 26 GHz ± K-band

Small Process Connections

Very little ³near zone´

Recessed in nozzles

Less susceptible to false echoes

Reduced antenna size

Perfect for small vessels

� Able to measure lower dK

products without using a

stilling well.

Typical accuracy +/- 3-5mm

No single frequency is ideally suited for every radar level application.




Guided Wave

Radar

(TDR)




Guided Wave Radar Measurement

Guided Wave Radar level measurement

� Time of Flight

� Top mounted

� Solids and liquids applications

� Contact Measurement

� GUIDED WAVE RADAR is virtually unaffected by

the following process conditions:

Temperature

Pressure and Vacuum

Conductivity

Dielectric Constant (dK)

Specific Gravity

Vapor, Steam, or Dust Air Movement

Build up (depends on type of build up)

Foam




Principle of Operation

�A microwave pulse (2 GHz) is

guided along a cable or rod in a20´ diameter or inside a coaxial

system.

�The pulse is then reflected from

the solid or liquid, back to thehead of the unit.

�The travel time of the pulse is

measured and then converted to

distance.




Application Examples

� Installation into the vessel

� Installation in bridles without

worry of build-up or

interference from side leg

connections

� Ideal for replacement of

displacers




Application Examples

� Interface Measurement

� Oil/Water

� Solvent/Water




Guided Wave Radar ± Accuracy & Dead Zones

Typical Accuracies

� Cable +/- 5 mm

� Rod +/- 5 mm

� Concentric Tube +/- 3 mm

Typical Dead Zones or Blocking Distances

Cable

� Top 6 inches

� Bottom 9.8 inches

includes weight ± 6´

Rod

� Top 6 inches

� Bottom 0 inches

Concentric Tube

� Top: 1.6 inches

� Bottom: 0.8 inches




Ultrasonic




Ultrasonic Level Measurement

Ultrasonic level measurement

Time of Flight

Top mounted

Solids and liquids applications

Non-contact

ULTRASONIC is virtually unaffected by thefollowing process conditions:

Change is product density (spg)

Change in dielectric constant (dk)




Ultrasonic Level Measurement ± How it works

Time of Flight Technology

Short ultrasonic impulses emitted fromtransducer

Bursts are created from electrical energy

applied to piezeo electric crystal inside thetransducer

The transducer creates sound waves(mechanical energy)

With longer measuring ranges a lower frequency and higher amplitude are needed

to produce sound waves that can travelfarther

The longer the measuring range thelarger the transducer must be




Ultrasonic Level Technology ± Advantages

Can be mounted in plastic stilling wells

Narrow beam angles minimize effect of

obstructions

Swivel flange available for applications with

angles of repose

Familiar technology throughout the industry,

therefore, often a trusted technology throughout

the industry

Cost-effective




Ultrasonic Level Technology ± When to use it

Vessels with products whose characteristics

remain constant

Water

Bulk solids

Storage Vessels

Where repeatability is not critical

Typical Accuracy +/- 5-10 mm




Questions?

Questions?

Radar and Ultrasonic Level Measurement

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