Level Measurement Transmitters “Applying Level Measurement”

10/20/2017

1

09/08/2017

Products Solutions Services

Level Measurement Transmitters

“Applying Level Measurement”

Slide 1 Bill Sholette 09/08/2017

Ultrasonic

FDU91

FDU93

FDU95

FDU92

FDU90

Installation Guidelines ToF Level Products

Slide 2 Bill Sholette

09/08/2017

The Principle – Time of Flight (TOF)

Emission of ultrasound pulses

Reflection of the pulses from the

product surface

Receiving of the reflected pulses

Measurement of the Time of Flightcalculation of the distance between the device

and the product surface by

00.40

2d = c

emitting

receiving



Environmental effects on velocity of sound

Temperature0.17% /°C

measured/compensated

Air moisture0.3% withchange inrelative moisturefrom 0 to 100%

Pressure change 30bar /435psichange in run timeapprox 0.3%pmin = 10psia

Velocity of sound co = 331.6m/s (1088ft/s)

Vapor pressure< 50mbar (20°C)?

irrelevant

c = M

=

= 344m /s (1088ft/s)

28.8

cair at 20°C =

x Rm (273 + T)

1.4 8314.3 (273+20)

c: velocity of sound [m/s]Rm: universal gas constant

(8314,3 J/kmol k)T: temperature [°C]x: adiabatic index

insignificant

no problem

M: molecular weight



09/08/2017

Speed of Propagation for Ultrasound

pressure: no influencetemperature: approx. 0.17 % / K

(air: 0.59 cm / K)

C p C TS

0 1273K

p

r

k

T

C0

=

=

=

=

=

pressure

density

adiabetic exponent

temperature

speed of ultrasound at 0°C

example: filling of chlorine tankAir: 334 m/s (1095 ft/s)Cl: 206 m/s (676 ft/s) failure: 38%

GasSpeed [m/s]

Speed [ft/s]

CI 206 676

CO2 258 846

Ar 308 1010

O2 32°F 315 1033

O2 ‐300°F 178 584

NO 324 1063

Air 32°F 331 1086

Air +68°F 334 1096

Air +104°F 355 1165

CO 337 1106

N2 377 1237

Coal gas 441 1447

Helium 32°F 971 3186



Ultrasonic Mounting



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Reflection of Acoustic Energy

• ideal conditions • “light“ foam

• big bubbles

• low density

• condensed foam ,

heavy, small bubbles• high density

“something in‐between“

‐‐> signal absorption

???



Self Cleaning Transducer Face

FDU91 FDU92

Advantage

Because of an optimized coupling between piezo crystal and membrane much more mechanical force is applied to the membrane strong self cleaning effect (e.g. for condensation conditions)



09/08/2017

Free Space Radar Installations



Basics Reflection

Water

Air

r=80

r=1

=1.00

=0.001

Radar in comparison to Ultrasonic

r : dielectric constant : specific density



09/08/2017

Basics ReflectionRadar in comparison to Ultrasonic

Air

Oilr=2 =0.85

r=1 =0.001

Shift caused by slower speed of propagation in oil

r : dielectric constant : specific density



Radar Mounting

• Recommended distance from outer wall

is 1/3 diameter of vessel.• FMR 230/231 minimum distance to wall =

12 inches

• FMR 240/244/245/250 Minimum distance

to wall = 6 inches

Note – It may be desirable to mount the radar closer to a wall to help ignore internal tank obstructions (i.e. agitators). Always observe minimum distance to tank wall requirements.



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Radar ‐ Mounting

A position away from the filling stream will avoid interference echoes. Echoes from fittings are suppressed during calibration

A position above the filling stream will be subject to interference echoes



Radar ‐ Mounting

A central position strengthens double echoes

A non‐central position avoids double echoes

Min. 12” off wall



09/08/2017

Radar Installed in the Middle of a Dome Vessel

• Radar unit “jumps” between

level signal first harmonic second

harmonic

• Special settings have to be made

to detect the fist echo

(Fist Echo Factor)

• This scenario can be avoided by a

different installation



Radar Plastic Tanks

When measuring in plastic tanks, Microwave energy can penetrate and reflect off external metal structure.



09/08/2017

Dealing with Condensation



FMR 245/244 with Condensation

with condensation[water, ~ 113°F (45°C)

w/o condensation

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Guided Wave Radar (TDR)



TDR ‐ Principle of Operation

typical envelope curve:

amplitude

End of probe

Level

Reflection fromprocess connection

SandPowdered clayFly ashTalcumLime

8”

80% of the energy

is concentrated

within a

radius of 8”!



09/08/2017

Guided Wave Radar Installation

• Minimum Dimension “A”Smooth Metallic Walls = 2 inchesPlastic Walls = 12 inches from

external metal obstructionsConcrete Walls = 36 inches

• Minimum Dimension “B”12 inches from obstruction

• Minimum Dimension “C”Rope Probe = 6 inchesRod Probe = 0.4 inchesCoax Probe = 0.4 inches

Note – For Coax Probes, Distance from wall or internal obstructions are irrelevant.



Guided Wave Radar – Nozzle Mounting

• longitudinal resonances in

long (Greater than 6“), narrow

nozzles no additional ringing

Long Nozzle Lengths are possible. Dielectric?

Span Range?

• lateral resonances in nozzles with

large diameters (Greater than 6“) significant additional ringing

reduced signal / noise ratio

nozzle diameter >6” require

special installation considerations !



09/08/2017

What about Probe Build Up?


Slide 23

buildup reflection

level reflection

09/08/2017

Guided Wave Radar in Plastic Vessels or Silos

Metal flange 4 inch minimum *

Metal plate Ø approx 8 – 12“

Silo roof

use a reflector (flange, metal plate) in plastic silos

without reflector

* Note – with high dielectric material a 2 inch flange

is possible



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09/08/2017

Results of Radar and Guided Wave Radar Foam Test

Comparison of guided radar, free space radar at 6 GHz and free space radar

at 26 GHz in an application with low density foam



Capacitance

Capacitance Technology



09/08/2017

Capacitance Probe as a Component of a Capacitor

• Brief over view of capacitance

_

+

SS rod

Material

Tank wall[metal]



Electronic Build‐up Compensation

Standard insulated probe with conductive buildup for a continuous level

application

Now this circuit has a phase shift of approximately 45°between the current and the voltage instead of the 90°with no buildup.

The electronics can sense this phase shift and compensate for this built‐up effect on the circuit

Process

Rod

Tank Wall

The buildup adds extra capacitance and resistance to the circuit

Build‐up effect



09/08/2017

Buildup, Continuous Systems (Liquicap M)

Ciso I

F

Ciso

IMeas

UMess

Cbuild up Rbuild upCbuild up

Rbuild up

Fully insulated probe

Tank wall

Conductive Liquid, conductive build up,standard mode

UMeas

ILevel

IR_build up

IMeas

- 45°



Products Solutions Services

Tuning Fork Technology


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Point Level Instruments: Typical Installation

• Overspill protection

• MAX‐point level

• MIN‐point level

• pump protection



Characteristics of universal limit switches

• “active“ measurement principle

• independent of installation position and direction

• no calibration

• independent of process influences

(e.g. pressure, temperature, ...)

• independent of substance characteristics

(e.g. conductivity, dielectric constant, density, viscosity, ...)

• independent of • ‐ gas bubbles

• ‐ foam

• ‐ solids (dirt, soiling) in process liquid



09/08/2017


Self Diagnostics Liquiphant M/S (FEL 51… 67)• Continuous monitoring of vibration frequency

• Reliable alarm function with each electronic insert!

sensor‐slarm

0,4 s delayed

400fa‐15%

fafa+ 6,5%

1500 f [Hz]

25

0

0

Submersion depth of fork [mm]

corrosionalarm

60 s delayed

sensor‐alarm

0,4 s delayed

Normal operation

fa‐15% switch point at ca. 850 Hz

ALARM

fa =vibration frequency in air ≈ 1 kHz

ALARM


Operation Independent of Medium Properties

changing media

foam

air bubbles

built‐up

pressure andtemperature change

plant vibration

viscosity change

turbulences

suspension

electrical properties



09/08/2017

So, What Technology Is The Right Choice?

• There are many technologies for measuring

level. All have good and bad applications.



Ultrasonic

• Positive• The default standard for Open Channel Flow

• Lower cost than Radar or GWR

• Non‐Contact Technology

• Great for water storage tanks

• Not dependent on Dielectric Constant

• Caution• Patchy foam on surface

• Dusty applications (solids)

• Ice on transducer face (Heated Sensors are available)

• Avoid• Vapors

• Foam Blanket



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Radar

• Positive• Not affected by vapors

• Non‐contact Technology

• Not affected by dust

• Caution• Foam

• Low Dielectric Materials (below 1.8DK)

• Plastic Vessels

• Avoid• Dielectric below 1.4DK



Guided Wave Radar

• Positive• Focused energy better with low dielectric

• Performs well when foam is present

• Caution• Contact technology – compatibility

• Long Nozzles

• Agitated Vessels

• Concrete Vessels

• Plastic Vessels

• Avoid• Dielectric below 1.2DK



09/08/2017

Capacitance

• Positive• Real time measurement

• Excellent for short span applications


• Agitated Vessels

• Avoid• Semi conductive materials (greater then I microsiemens but less than 100)

• Non stable dielectric properties




Tuning Fork

• Positive• No Calibration – simple commissioning

• No moving parts

• Can be mounted in any orientation

• Not affected by suspended solids or entrained air


• Agitated Vessels – may require support

• Avoid• Viscosity over 10,000 centipoise


09/08/2017

Chemical Storage

• Bulk Storage

• Day Tanks

• Portable Tanks• Depending on the vessel

type and the material

being measured,

Ultrasonic, Guided Wave,

Free Space Radar, or

Capacitance could be the

best solution.

• For hazardous Chemicals,

Point Level Overfill back

up is recommended


Pump Protection

• A point level switch

mounted in the

pipe feeding a

pump will indicate

when the pipe is

empty. This will

prevent running the

pump empty

causing stator and

seal damage


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09/08/2017

Level measurement in storm water basin

Requirements

Level measurement in a storm

water basin

Control and recognition of the

overload amount to the sewage

treatment plant

Solution

Prosonic S with FDU91 sensor and

mounting angle

Flood‐proof sensor according to

IP68/NEMA6P


Level measurement in a reservoir

Requirement

Level measurement in a process

water reservoir

Solution

Prosonic T/M

Easy and fast commissioning

with an attractive price


09/08/2017

Level measurement above a filter

Requirement

Level measurement above a

filter

Solution

Prosonic T/M with mounting

angle

Easy and fast commissioning

with an attractive price


Water Well Level

• Hydrostatic

Pressure

Transmitters

are the

standard for

water well

measurement


09/08/2017

Sludge Level in Clarifiers

• The CUS71D transmitter

measures the interface

between the water and

settled sludge in primary

and secondary clarifiers.


Questions?



Documents

Level Measurement Transmitters “Applying Level Measurement”