Flow measurement Cảm biến lưu lượng

The participant knows… • … coriolis, electromagnetic, vortex and thermal flow measurement principle • …application and installation limits The participant understands… • …each measurement technology has different limitation • … appli ti d diti d i t ll ti cation and process conditions and installations are very important

Products Solutions Services

Flow Measurement

Learning Objectives

10/13/2015

The participant knows…

• … coriolis, electromagnetic, vortex and thermal flow measurement principle

• …application and installation limits

The participant understands…

• …each measurement technology has different limitation

• … application and process conditions and installations are very important

The first step to find the solution

di t

Installati

on situation

Require

d t

Accepta ble pressur

e loss

accurac y

direct or calculate d

E

d down

turn-Etc.

Influences on the selection of the measuring system

10/13/2015

Mass

or Volume Viscosity

C d

Liquid / Gas

Abrasion

Corrosio n

Pressur e

Conduc tivity

Best fit measuring system

Price Density

system

Accepte

d pressure loss Temp.

Pipe inlet

Turn down Flow

Disturb

Homog eneity Pipe

profile ances

Rough classification of applications

10/13/2015

• Conductive liquids

>80% of all liquids are conductive (Drinking- and waste water, beverages acids alkalines etc )

beverages, acids, alkalines, etc.)

• Non conductive liquids

Oils, hydro carbons, liquefied gases, demineralized water

Abrasive slurries, custody transfer, measurement from

outside, bidirectional, etc

Flow technologies overview

Application Range

10/13/2015

Coriolis 200

Magnetic Inductive

pressure [bar]

Thermal Ultrasonic

Products Solutions Services

Flow Measurement – Coriolis Measurement

The Coriolis Measuring Principle

10/13/2015

Inventor of the measuring principle

of the same name.

Caspard Gustave de Coriolis

Coriolis flow meter advantages

10/13/2015

• Universal measuring principle for liquids and gases

• Simultaneous and direct measurement of mass

flow density temperature and viscosity

flow, density, temperature and viscosity

• Not affected by flow profile

• No inlet/outlet runs necessary

Coriolis flow meter disadvantages:

10/13/2015

• Relatively high initial investment.

• Outlay for installation can be considerable, depending on the design and manufacturer

and manufacturer.

• Limited temperature range: typically –50 to +350 °C (–60 to +660 °F).

• Restricted usability if the gas content of the fluid is high and in the case of multi-phase fluids.

• Larger sizes are heavy in some designs.

Products Solutions Services

Flow Measurement – Electromagnetic Measurement

The Electromagnetic Measuring Principle

10/13/2015

Michael Faraday

Basics of Electromagnetic Measurement

Flow

A voltage is induced in an electric conductor is moved

Basics of Electromagnetic Measurement

OHNE DETAILS

Flow

v L B

A Pipe area

Basics of Electromagnetic -Various EMF Design

Flow

Basics of Electromagnetic - Ranges of Conductivity in Liqui

Flow

0.05 µS/cm

Oil, Hydrocarbons Ultra pure water

1 µS/cm

10 µS/cm

Pure water Water:

Min Conductivityfor EMF’s

1 mS/cm

10 mS/cm

Potable water

Beer Milk Orange juice Food:

100 mS/cm

1000 mS/cm

Apple juice Tomato juice

Phosphoric acid Sulphuric acid Process:

Basics of Electromagnetic - Empty Pipe Detection (EPD)

Basics of Electromagnetic - Reference Electrode

Flow

EPD electrode

Measuring electrode

Measuring electrode

Reference electrode

ECC inhibits the build-up U

ECC inhibits the build up

of (conductive) coating

Electromagnetic flow meter advantages

• High degree of measuring dependability and

reproducibility, good long-term stability

Electromagnetic flow meter disadvantages:

10/13/2015

• Only conductive liquids can be measured

• Measurement is less accurate and more difficult if the liquid is onl eakl conducti e e g ith

the liquid is only weakly conductive, e.g with demineralized water

• Deposits inside the measuring tube or on the

electrodes can cause errorselectrodes can cause errors

Products Solutions Services

Flow Measurement – Ultrasonic Flow Measurement

Ultrasonic Flow Measuring Principle

10/13/2015

Lord Raleigh

Doppler Measuring Principle

• Average received frequency is subtracted from the generated

frequency (0.5 -1MHz)

• Frequency difference varies directly with flow speed

• (typically 80-120Hz for each (typically 80 120Hz for each ft/s of velocity)

• Non-moving reflectors do not produce a frequency hif

Δf ~ Q Q shift

Δf = frequency differential

• Liquids with high solids or aeration

• Wastewater treatment, Slurries, Inhomogeneous liquids

• not suitable for pure or particle free liquids

• poor flow average; measures particle flow speed and not whole profile

• poor flow average; measures particle flow speed and not whole profile

• subject to pipe vibration and EMI from VF Drives

Transit-Time Measuring Principle

Δt ~ QV

• Disadvantages:

• Dependent upon pipe

• Cs = s.v.sensor (7,874ft/s)

• Cp = s.v pipe material (10,500ft/s)

C di (3 280 6 560ft/ ) • Dependent upon pipe

and liquid data

• Cm = s.v medium (3,280 6,560ft/s)

• α decreases as s.v of Cm decreases

Insertion Sensor

• Wetted type

• Installation by means of weld-in type socket on anweld in type socket on an existing pipe

• Requires a weld able pipe

• Requires a weld able pipe material

• Dependent upon pressure

• Process interruption forProcess interruption for

• High accuracy because pipe geometry and

pipe geometry and sensor mounting controlled

• Can be calibrated

• Disadvantages:

• Process interruption

Ultrasonic flow meter advantages

10/13/2015

• With homogeneous fluids, the principle is independent of pressure, temperature, conductivity and viscosity

• Usable for a wide range of nominal diameters (DN 15 to 4000)

• Usable for a wide range of nominal diameters (DN 15 to 4000)

• Application-specific clamp-on and inline sensors

Clamp-on sensors:

– versatileversatile

– ideal for retrofitting without process interruptions

– aggressive fluids can be measured without a problem(even at high pressure)

Inline sensors:

– for guaranteed accuracy

– robust design (fully welded) for direct installation in the piping run

• No pipe constrictions, no pressure losses

• No moving parts Minimum outlay for maintenance and upkeep

• High life expectancy (no abrasion or corrosion by the fluid)

Ultrasonic flow meter disadvantages:

10/13/2015

• Measurement results are highly dependent on flow profile, because fluid velocity is measured only on

a narro path or a small area

a narrow path or a small area

• Medium to low accuracy Strongly dependent on fluid properties (acoustic transparency)

• Deposits (pipe/sensor) lead to measuring errorsDeposits (pipe/sensor) lead to measuring errors and to failure

• The Doppler method can be used only in certain applications, e.g for flow monitoring

• Limitations:

- If the fluid is heavily contaminated with foreign matter

- Limited fluid temperature ranges

- If flow profile is subject to severe disruption

Products Solutions Services

Flow Measurement – Thermal Flow Measurement

Thermal Flow Measuring Principle

10/13/2015

Louis Vessot King

Basics of Thermal Flow Measurement

Mass flow measurement based on thermal dispersion

• A heated temperature sensor is

kept at a constant differential

temperature from the gas

reference sensor

reference sensor

• The cooling effect generated by

mass flow causes an increase in

sensor power to maintain the

temperature differential

• The power supplied to theThe power supplied to the

heated sensor is proportional to

the mass flow

Thermal sensors (PT100)

Influence of pressure and temperature

• The thermal properties of gases changes as pressure and

temperature changes

• The influence is different for different gases e.g Air is more

temperature dependent where CO2 is more affected by changing

pressure

• Temperature is dynamically compensated – gas temperature is

measured live and the gas properties are updated in real time

• For stable pressures the pressure is a set value in the HMI

• For large swings in pressure i e >5 bar a remote pressure input can

• For large swings in pressure i.e >5 bar, a remote pressure input can

be used via mA input or PROFIBUS or Modbus RS485

Influence by moisture

• Moist gas will increase the cooling effect on the sensors

• This influence is minimal as long as condensation is avoided

• Changes in humidity will affect the output by up to 7 % throughout the yearly seasons

• In case of condensation on the transducer, the meter will typically goIn case of condensation on the transducer, the meter will typically go full-scale

If process temperature < dew point = condensation

CONSIDER PROCESS PRESSURE !!

• If the individual components have similar properties, a change won’t have a drastic influence on the meter performance e.g Air and N2 Changing gas fractions of He or H2 will change the mixture properties significantly and will lead to large measurement errors

significantly and will lead to large measurement errors

• Refer to Applicator® !

Thermal flow meter advantages

10/13/2015

• Measures mass flow directly - without additional pressure and

temperature inputs

• Accurate measurement and operation at very low gas pressures and flow

• Accurate measurement and operation at very low gas pressures and flow rates

• Negligible pressure drop

• Wide turndown capability (up to 100:1)Wide turndown capability (up to 100 1)

• Economical solution for large diameters

• Measurement in rectangular ducts

Thermal flow meter disadvantages

• Dependent upon inlet/outlet run

• Sensitive to gas properties and unstable mixturesg p p

• Only for a defined range of common gases

• Not a very high accuracy class or custody transfer meter

• Limited temperature and pressure range

Despite the disadvantages, it is often the only measuring principle which meets the application requirements!

Products Solutions Services

Flow Measurement – Vortex Flow Measurement

The Vortex Measuring Principle

Leonardo Da Vinci Theodor von Karman

Vortex flow meter advantages

10/13/2015

• Universal applicable for volumetric flow

measurement of steam liquids and gas

measurement of steam, liquids and gas

• Largely unaffected by changes in pressure,

temperature and viscosity

• Simple and low cost installation

• Low pressure drop

• Wide measuring range

• Independent of the process conditions and fluid

• Long-term stability ( lifetime K factor)

Vortex flow meter disadvantages

• Pulsating flow and swirl have a detrimental effect on measuring accuracy

• Long inlet and outlet runs necessary

• Can not be used for highly viscous fluids

• Measurement with low velocities not possible (Re<4000)

Products Solutions Services

Flow Measurement – DP Flow Orifice

Measuring Principle for Orifice – Nozzle - Venturi

Daniel Bernoulli Giovanni Battista Venturi

Basics of DP Flow Measurement

Dp Flow measurement with orifice plate

Dp Flow measurement with nozzle

Dp Flow measurement with venturi tube

Products Solutions Services

Flow Measurement – DP Flow Pitot Tube

Dp flow meter advantages

• Differential pressure transmitters can be

replaced during operation without process

shutdown

• Robust design; no moving parts

Dp flow meter disadvantages

• Suitable for low-viscosity fluids up to 50 mPas

• When used for metering gas flow, process conditions (pressure,

temperature) should be as constant as possible, if not flow computer can utilize local temperature and pressure measurements to

compensate the flow signal for process variations

• Short batching cycles are not possible

• For remote version, the measuring system may need additional valves and impulse lines

Conclusion

• Unfortunately, a single-flow measurement technology,

is not good enough……

is not good enough

• Best flow measurement technology would be very

different, according to application , g pp