Flow Measurement Some Basic Terms and Concepts

1
Flow MeasurementSome Basic Terms and Concepts

• Fluid - The state of a substance in which its
  particles easily move and change their relative
  position without a separation of the mass and
  that easily yield to pressure. A fluid can be a
  liquid (generally considered incompressible) or a
  gas.
• Mass - Quantity of matter that causes it to have
  weight in a gravitational field. Mass flow is
  expressed in weight/time, ie kilograms/hr.
• Volume - Space occupied or enclosed by cubic
  units. Volumetric flow is expressed in cubic
  measure/time i.e. cubic feet/minute or
  gallons/hour.
• Density - Mass of a substance per unit volume.
• Specific Gravity - The ratio of the density of a
  substance to the density of some some substance
  taken as a standard. For flow of liquids,
  specific gravity of fluid is compared against
  that of water, for gases against that of air.
• Mole - grams/molecular weight
• SCFM - Standard Cubic Feet per Minute.

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Flow MeasurementSome Basic Terms and Concepts

• Liquids are generally considered incompressible
• Ideal Gas Law - The pressure, temperature and
  volume of a gas are all interrelated.
• PV nRT
• P pressure of the gas
• V the volume that the gas occupies(ie ft3)
• n number of moles
• R ideal gas constant (a universal constant)
• T temperature of the gas in absolute units
• For the gas industry flow is most commonly
  measured as volumetric flow and expressed at base
  conditions
• volume is dependant on temperature and pressure
  and composition
• volumetric measurement must be corrected back to
  base conditions
• usually 60 - 700F and 1 atmosphere (14.73 psia)
  pressure

3
The Object of Flow Measurement

• How much went from one place to another?
• Volumetric
• corrected to base pressure and temperature
• Mass
• Mass is mass. It doesnt change with changes in
  temperature or pressure.

4
A Variety of Flow Measurement Methods

• Orifice plate meter
• Most common in the gas industry
• Relatively low rangeability
• Least accurate of all popular methods
• High installation cost
• No moving parts low (or no) maintenance
• No calibration little maintenance
• Intrusive device

5
Orifice Plate Meter
Differential Pressure
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A Variety of Flow Measurement Methods

• Turbine Meter
• Most common meter type across all industries
• Second most common in the gas industry
• Much more accurate than orifice plate
• Wide flow rangeability
• Low relative cost to purchase but comparatively
  high cost to maintain
• Has moving parts that can fail but is easily
  field repaired
• Requires calibration
• Intrusive device

7
Turbine meters

• Use a vaned rotor engaged by the flowing fluid
• the fluid spins the rotor at an angular velocity
  proportional to the flow rate
• As the turbine rotates, an AC voltage is induced
  in a magnetic pickup
• mounted externally to the fluid process

• As each turbine blade passes the pickup the total
  magnetic flux density is changed
• induces a single voltage pulse
• Each pulse represents a finite volume of fluid
  that has been displaced through 2 adjacent rotor
  blades.

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A Variety of Flow Measurement Methods

• Positive displacement meter
• Most accurate
• Uses standard low speed digital input on PLC
• Other less common types
• Venturi meter
• Ultrasonic meter
• Vortex meter
• Lots more

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Flow Measurement by the Orifice Plate Method

• Origins of the fluid flow Laws
• More than 300 years ago, Charles and Boyle
  discovered that
• Uf1 (P h)1/2
• The formula looks deceptively simple
• Qb (218.573Cd(FT)EvY1d2Tb/Pb)(Pf1Zb Zb
  airhw/GiZf1Tf) ½
• And it would be,

10
Flow Measurement by the Orifice Plate Method

• Origins of the fluid flow Laws
• More than 300 years ago, Charles and Boyle
  discovered that
• Uf1 (P h)1/2
• The formula looks deceptively simple
• Qb (218.573Cd(FT)EvY1d2Tb/Pb)(Pf1Zb Zb
  airhw/GiZf1Tf) ½
• And it would be, except each component of the
  equation,

11
Flow Measurement by the Orifice Plate Method

• Origins of the fluid flow Laws
• More than 300 years ago, Charles and Boyle
  discovered that
• Uf1 (P h)1/2
• The formula looks deceptively simple
• Qb (218.573Cd(FT)EvY1d2Tb/Pb)(Pf1Zb Zb
  airhw/GiZf1Tf) ½
• And it would be, except each component of the
  equation, for example the Coefficient of
  discharge term, relies on solving an equation
  like this

12
Flow Measurement by the Orifice Plate Method

• Origins of the fluid flow Laws
• More than 300 years ago, Charles and Boyle
  discovered that
• Uf1 (P h)1/2
• The formula looks deceptively simple
• Qb (218.573Cd(FT)EvY1d2Tb/Pb)(Pf1Zb Zb
  airhw/GiZf1Tf) ½
• And it would be, except each component of the
  equation, for example the Coefficient of
  discharge term, relies on solving an equation
  like this
• Cd(FT) Ci(FT).000511(106 ß/Red)0.7((0.0210.004
  9(19,000ß/ Red)0.8) ß4(106/ Red)0.35

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Flow Measurement The Names and Numbers to Know

• For measuring flow there are 3 equations that are
  the most common
• For orifice plate meters, AGA 3
• 1992 version
• 1985 version
• ISO 5167 is equivalent and is very similar
• ISO is currently upgrading and will probably come
  into lock step with AGA
• For turbine meters AGA 7
• AGA 7 is a relatively simple equation compared to
  AGA 3
• Uf1 (f/K)M

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Flow Measurement The Names and Numbers to
Know(contd)

• For high accuracy gas measurement a
  compressibility and sometimes supercompressibility
  equation is needed
• AGA 8 Most common
• 2 versions
• 1985
• 1992(ISO12213)
• Multiple methods
• Gross methods
• 2 for 1992 (recommended method for use between 32
  to 130 oF and less than 1,200 psia, provided the
  gas composition is within the normal range)
• 4 for 1985
• Detailed methods
• 1992 is the most accurate and most common

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Flow Measurement The Names and Numbers to
Know(contd)

• Other compressibility equations(in order of
  popularity)
• NX-19 (developed in 1962)
• Still used frequently in high C02 applications
• Compressibility equations used for special gas
  compositions
• Soave Redlich Kwong (SRK)
• Wichert Aziz

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Flow Measurement The Names and Numbers to
Know(contd)

• API 2540
• Used for liquid measurement with turbine or
  rotary displacement meters
• Provides temperature and pressure compensation

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Flow MeasurementPutting it all Together

• For measuring gas with an orifice plate meter use
  one of these
• AGA 3 alone
• AGA 3 with AGA 8
• AGA 3 with NX-19
• AGA 3 with other

18
Flow MeasurementPutting it all Together (Contd)

• For measuring gas with a turbine meter
• AGA 7 alone
• AGA7 with AGA 8
• AGA7 with NX-19
• AGA7 with other

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Flow MeasurementPutting it all Together (Contd)

• For measuring liquid with an orifice plate meter
• AGA 3 alone
• For measuring liquid with a turbine meter
• AGA 7 alone
• AGA 7 with API 2540
• For measuring liquid with a rotary displacement
  meter
• API 2540

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Flow MeasurementAPI 21.1 Audit Trail and Event
Log

• Custody transfer applications are those where the
  fluid being measured changes ownership at the
  meter point
• If the measurement application is not custody
  transfer it is
• Allocation (often requires API 21.1 for
  convenience)
• Control
• For custody transfer applications a detailed
  audit trail and event log are required
• The Industry expects a minimum of
• 7 days of hourly averages of specified variables
• 35 days of daily averages of the same variables
• A copy of the configuration of the meter
  parameters
• A 100 entry time stamped log of events
• All parameter changes
• Alarms

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Flow MeasurementIf You Dont Know for Sure, Just
Ask

• If a customer says he needs an RTU that does AGA
  that doesnt mean anything!
• Ask the customer some basic questions and consult
  your notes.
• What is being measured?
• What kind of meter do they have?
• How accurate does the measurement need to be?
• Is the customer doing custody transfer?
• If a customer is just doing control based on flow
  measurement
• AGA 3 or 7 alone are often accurate enough.

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What is the Market for Flow Meters

• Orifice Plate Meters
• New installations projected to be
• mil.
• Revenues bil. Increasing by annually through
  2002
• Turbine Meters
• New installations projected to be
• Revenues mil. Increasing by annually through
  2002
• Source Frost Sullivan Worldsearch May,1996

Under Construction
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What does Schneider offer?Orifice plate meters

• Starling Associates Gas Flow Loadable Function
  Block Library
• To run loadables on a continuous basis you must
  use the proper enabler, 130 HEK 301 01 or 130 HEK
  301 02
• Fits in the bus expansion port of a Compact or
  Micro PLC.
• Disallows the use of the AS HDTA 202 2 slot rack.
• Must be used with a IA WBXT 204 cable if an AS
  WBXT 201 is used.
• Loadables can be run, without an enabler, in demo
  mode for 48 hours after program load.

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What does Schneider offer?Orifice plate meters
(continued)

• Starling Associates Gas Flow Loadable Function
  Block Library
• consists of 5 blocks that cover the different
  calculation combinations

• G392 - up to 8 meters of AGA 3 1992 alone. API
  21.1 audit trail
• GD92 - meter of AGA 3 1992 and AGA 8 detailed
  method.
• GFNX - up to 8 meters of AGA3 1985 and NX-19.
  API 21.1 audit trail
• GG92 - up to 8 meters of AGA 3 1992 and AGA 8
  both gross methods. API 21.1 audit trail
• GM92 - up to 8 meters of AGA 3 1992 and AGA 8
  detailed method. API 21.1 audit trail

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What does Schneider offer?Orifice plate meters
(continued)

• Flow calculations run only on Compact and Micro
  612 04 CPUs
• Except for the 612 04 you must have a minimum of
  16K 984 LL capable CPU to run GG92, GFNX or GM92
• The 612 04 is a special case which can run any of
  the flow loadables and have a large amount of
  program space left.
• GD92 and G392 may be run in as small as a Compact
  141 CPU
• Using these loadables in an 8 K controller leaves
  little space for other programming.

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What does Schneider offer?Turbine meters

• AS BVRC 200, AS BCTR 205 and AS BCTR 224
• High speed counter input cards, for the Compact
  and Modicon Micro, that perform the AGA 7
  Calculation in the module
• K and M factors are configured in the module
  and a corrected count or rate is delivered to the
  CPU.
• BVRC 200 takes direct turbine meter sine
  frequency input signal
• BCTR 205 and 224 take square wave DC input
  signals, 5 VDC and 24VDC respectively.
• API 2540 temperature compensation and pressure
  compensation is currently not supported as a
  solution but can be programmed by the end user.

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What does Schneider offer?Orifice plate meters
(continued)

• Flow calculations run only on Compact and Micro
  612 04 CPUs
• Except for the 612 04 you must have a minimum of
  16K 984 LL capable CPU to run GG92, GFNX or GM92
• The 612 04 is a special case which can run any of
  the flow loadables and have a large amount of
  program space left.
• GD92 and G392 may be run in as small as a Compact
  141 CPU
• Using these loadables in an 8 K controller leaves
  little space for other programming.