MEASUREMENT OF GAS BY MEASUREMENT OF GAS BY MULTIPATH ULTRASONIC METERMULTIPATH ULTRASONIC METER

AGA REPORT NO. 9AGA REPORT NO. 9

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998

1.1. IntroductionIntroduction2.2. TerminologyTerminology3.3. Operating ConditionOperating Condition4.4. Meter RequirementMeter Requirement5.5. Performance RequirementPerformance Requirement6.6. Individual Meter Testing RequirementIndividual Meter Testing Requirement7.7. Installation RequirementInstallation Requirement8.8. Field Verification TestField Verification Test

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 1.1. IntroductionIntroduction1.1 Scope:1.1 Scope:

““Developed for multipath ultrasonic transit time flow meter”.Developed for multipath ultrasonic transit time flow meter”.

1.2 Principle of measurement.1.2 Principle of measurement.““The meter measured gas flowrate by measuring transit times of The meter measured gas flowrate by measuring transit times of high-frequency sound pulses” high-frequency sound pulses”

The Accuracy of USM depends on several factor, such The Accuracy of USM depends on several factor, such as:as:

- Precise geometry of the meter body and ultrasonic transducer Precise geometry of the meter body and ultrasonic transducer location.location.

- The integration technique inherent in the design of the meter.The integration technique inherent in the design of the meter.- The quality of flow profile, levels of pulsation in the flowing gas The quality of flow profile, levels of pulsation in the flowing gas

stream and gas uniformity.stream and gas uniformity.- The accuracy of the transit times measurement.The accuracy of the transit times measurement.

continue continue

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998

The Accuracy of transit time measurement depends The Accuracy of transit time measurement depends on:on:

- The electronic clock stability.The electronic clock stability.

- Consistent detection of sound pulse wave reference position.Consistent detection of sound pulse wave reference position.

- Proper compensation for signal delays of electronic components Proper compensation for signal delays of electronic components and transducers. and transducers.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998

3. Operating condition:3. Operating condition:3.1 Gas quality3.1 Gas quality

The meter shall operate with any of the “normal range” natural The meter shall operate with any of the “normal range” natural gas composition mixtures specified in AGA Report No. 8.gas composition mixtures specified in AGA Report No. 8. (AGA 8, normal range natural gas mixtures)(AGA 8, normal range natural gas mixtures)

The manufacturer shall be consulted if any of the following are The manufacturer shall be consulted if any of the following are expected:expected:- Acoustic wave attenuating carbon dioxide level are above 10%.- Acoustic wave attenuating carbon dioxide level are above 10%.- Operating near the critical density of the natural gas mixtures.- Operating near the critical density of the natural gas mixtures.- Total sulfur level exceeds 20 grain per 100 cubic feet (320 ppm - Total sulfur level exceeds 20 grain per 100 cubic feet (320 ppm appox.).appox.).

AGA 8, Normal Range natural gas mixturesAGA 8, Normal Range natural gas mixtures

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 3.2 Pressure3.2 Pressure

The designer shall specify the expected minimum operating The designer shall specify the expected minimum operating pressure as well as maximum operating pressure.pressure as well as maximum operating pressure.

Ultrasonic transducer used in USM require minimum density (a Ultrasonic transducer used in USM require minimum density (a function of pressure) to ensure acoustic coupling of the sound function of pressure) to ensure acoustic coupling of the sound pulse to and from the gas.pulse to and from the gas.

3.3 Temperature, Gas and Ambient3.3 Temperature, Gas and AmbientThe designer shall specify the expected operating gas The designer shall specify the expected operating gas temperature range.temperature range.

The USM should operate over a flowing gas temperature range -The USM should operate over a flowing gas temperature range -1313oo – 131 – 131o o F. And operating ambient air temperature should be -F. And operating ambient air temperature should be -1313oo – 131 – 131o o F.F.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 3.4 Gas Flow Consideration3.4 Gas Flow Consideration

The flow-rate limits that can be measured by USM are determined by The flow-rate limits that can be measured by USM are determined by actual velocity of the flowing gas. The designer should determine the actual velocity of the flowing gas. The designer should determine the expected gas flow rates and verify that these value are within the expected gas flow rates and verify that these value are within the qqminmin, q, qtt and q and qmaxmax are stated by manufacturer. are stated by manufacturer.

The designer is cautioned to examine:The designer is cautioned to examine:

- Maximum velocity for noise and piping safety.- Maximum velocity for noise and piping safety.

- The direction of flow (Uni-directional or Bi-directional).- The direction of flow (Uni-directional or Bi-directional).

3.5 Upstream Piping and Flow Profile3.5 Upstream Piping and Flow ProfileUpstream piping configuration may adversely affect the gas velocity Upstream piping configuration may adversely affect the gas velocity profile entering a USM to such an extent that measurement error profile entering a USM to such an extent that measurement error occurs.occurs.

Further recommendations on upstream piping are provided in section Further recommendations on upstream piping are provided in section 7.7.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 4. Meter Requirement4. Meter Requirement4.1 Codes and Regulation.4.1 Codes and Regulation.

The meter body and other parts shall be designed and constructed of The meter body and other parts shall be designed and constructed of materials suitable for service conditions for which the meter is rated and materials suitable for service conditions for which the meter is rated and in accordance with codes and regulations as specified by designer. in accordance with codes and regulations as specified by designer.

4.2 Meter Body4.2 Meter Body4.2.1 Maximum Operating Pressure4.2.1 Maximum Operating Pressure

- Meter should be manufactured to meet one of the common pipe - Meter should be manufactured to meet one of the common pipe flanges.flanges.- The maximum design operating pressure of the meter should be the - The maximum design operating pressure of the meter should be the lowest of the max. design operating of the following: meter body, lowest of the max. design operating of the following: meter body, flanges, transducer connections, transducers assembly.flanges, transducer connections, transducers assembly.

4.2.2 Corrosion Resistance.4.2.2 Corrosion Resistance.All wetted part of the meter shall be manufactured of material All wetted part of the meter shall be manufactured of material compatible with natural gas and related fluids or as specified by the compatible with natural gas and related fluids or as specified by the designer.designer.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 4.2.3 Meter Body Lengths and Bores4.2.3 Meter Body Lengths and Bores

- Manufacturer should publish their standard overall face-to-face - Manufacturer should publish their standard overall face-to-face length of meter body with flanges, for each ANSI flange class and length of meter body with flanges, for each ANSI flange class and diameter.diameter.- The USM bore and the adjacent upstream pipe along with flanges - The USM bore and the adjacent upstream pipe along with flanges should have the same inside diameter to within 1% of each other.should have the same inside diameter to within 1% of each other.- For bidirectional application, both ends of meter should be - For bidirectional application, both ends of meter should be considered “upstream”. considered “upstream”.

4.2.4 Ultrasonic Transducer Ports4.2.4 Ultrasonic Transducer Ports- The transducer port should be designed in a way that reduces the - The transducer port should be designed in a way that reduces the possibility of liquids or solids accumulating in the transducer ports.possibility of liquids or solids accumulating in the transducer ports.- The meter should be equipped with valves and additional - The meter should be equipped with valves and additional devices, mounted on the transducer in order to make it possible to devices, mounted on the transducer in order to make it possible to replace the transducer without depressurizing the meter run.replace the transducer without depressurizing the meter run.

4.2.5 Pressure Tap4.2.5 Pressure Tap- At least one pressure tap shall be provided for measuring the - At least one pressure tap shall be provided for measuring the static pressure in the meter.static pressure in the meter.

4.2.6 Miscellaneus4.2.6 MiscellaneusThe meter should be designed in such a way that the body will not The meter should be designed in such a way that the body will not roll when resting on a smooth surface with slope of up to 10%.roll when resting on a smooth surface with slope of up to 10%.

4.2.7 Meter Body Marking4.2.7 Meter Body Marking

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 4.3 Ultrasonic Transducers.4.3 Ultrasonic Transducers.4.3.1 Specification.4.3.1 Specification.

The manufacturer should state the general specification of their The manufacturer should state the general specification of their ultrasonic transducers, such as critical dimension, max. allowable ultrasonic transducers, such as critical dimension, max. allowable operating pressure, operating pressure rating, operating operating pressure, operating pressure rating, operating temperature range and gas composition limitations. temperature range and gas composition limitations.

4.3.2 Rate of Pressure Change.4.3.2 Rate of Pressure Change.Clear instruction should be provided by the manufacturer for Clear instruction should be provided by the manufacturer for depressurization and pressurization of the meter during depressurization and pressurization of the meter during installation, start-up, maintenance and operation.installation, start-up, maintenance and operation.

4.3.3 Exchange4.3.3 ExchangeIt shall be possible to replace or relocate transducers without a It shall be possible to replace or relocate transducers without a significant change in meter performance.significant change in meter performance.

4.3.4 Transducer Test4.3.4 Transducer TestEach transducer or a pair of transducers should be tested and Each transducer or a pair of transducers should be tested and documented as part of the USM’s quality assurance program. documented as part of the USM’s quality assurance program.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 4.4 Electronic4.4 Electronic4.4.1 General Requirement.4.4.1 General Requirement.

- The USM’s electronic (SPU) systems: power supplies, microcomputer, - The USM’s electronic (SPU) systems: power supplies, microcomputer, signal processing components, and ultrasonic excitation circuits, should signal processing components, and ultrasonic excitation circuits, should be housed in one or more enclosure mounted on or next to the meter.be housed in one or more enclosure mounted on or next to the meter.- It should be possible to replace the entire SPU or change any field - It should be possible to replace the entire SPU or change any field replacement module without significant change in meter performance. replacement module without significant change in meter performance.

4.4.2 Output Signal Specification.4.4.2 Output Signal Specification.The SPU should be equipped with at least one of following output: serial The SPU should be equipped with at least one of following output: serial data interface, and frequency. data interface, and frequency.

4.4.3 Electronic Safety Design Requirements.4.4.3 Electronic Safety Design Requirements.The design of the USM including SPU shoul be analyzed, tested and The design of the USM including SPU shoul be analyzed, tested and certified by an applicable laboratory and labelled as approve for certified by an applicable laboratory and labelled as approve for operation in NEC class 1, Div. 2, group D Hazardous Area. operation in NEC class 1, Div. 2, group D Hazardous Area.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 4.5 Computer Program4.5 Computer Program4.5.1 Firmware4.5.1 Firmware

Computer code, flow calculation constants and operator entered Computer code, flow calculation constants and operator entered parameters should be stored in nonvolatile memory.parameters should be stored in nonvolatile memory.The manufacturer should record of all firmware revision and upgrade The manufacturer should record of all firmware revision and upgrade time to time to improve the performance of the meter.time to time to improve the performance of the meter.The manufacturer shall notify the operator if the firmware revision will The manufacturer shall notify the operator if the firmware revision will affect the accuracy of flow calibrated meter. affect the accuracy of flow calibrated meter.

4.5.2 Configuration and Maintenance Software.4.5.2 Configuration and Maintenance Software.The meter should supplied with software, with capability for local or The meter should supplied with software, with capability for local or remote configuring of the SPU and for monitoring the operation of the remote configuring of the SPU and for monitoring the operation of the meter. meter.

4.5.3 Inspection and Auditing Functions.4.5.3 Inspection and Auditing Functions.It should be possible for inspector/auditor to view and print the flow It should be possible for inspector/auditor to view and print the flow measurement configuration parameters used by the SPU, e.g: measurement configuration parameters used by the SPU, e.g: calibration constant, meter dimension, time averaging period and calibration constant, meter dimension, time averaging period and sampling rate.sampling rate.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 4.5.4 Alarms4.5.4 Alarms

The following alarms-status outputs should be provided in the form The following alarms-status outputs should be provided in the form of fail-safe, dry, relay contact or voltage free solid state switches of fail-safe, dry, relay contact or voltage free solid state switches isolated from ground. isolated from ground.

- Output invalid: when the indicated flow rate at line conditions is - Output invalid: when the indicated flow rate at line conditions is invalid.invalid.

- (optional) trouble: when any of several monitored parameter fall - (optional) trouble: when any of several monitored parameter fall outside of normal operation.outside of normal operation.

- (optional) partial failure: when one or more of the multiple - (optional) partial failure: when one or more of the multiple ultrasonic path is not usable. ultrasonic path is not usable.

4.5.5 Diagnostic Measurement.4.5.5 Diagnostic Measurement.

The following and other diagnostic measurement should be The following and other diagnostic measurement should be provided via serial data interface: average flow velocity, velocity of provided via serial data interface: average flow velocity, velocity of each path, SOS of each path, average SOS, status and each path, SOS of each path, average SOS, status and measurement quality indicators, alarm and failure indicators. measurement quality indicators, alarm and failure indicators.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 5. Performance Requirement5. Performance Requirement5.1 General 5.1 General

The performance of all USM shall meet the following:The performance of all USM shall meet the following:

Repeatability: Repeatability: ±± 0.2% for q 0.2% for qtt ≤≤ q qii ≤≤ q qmaxmax

±± 0.4% for q 0.4% for qminmin ≤≤ q qii << q qtt

Resolution: Resolution: 0.003 ft/s (0.001 m/s)0.003 ft/s (0.001 m/s)

Velocity Sampling IntervalVelocity Sampling Interval : : ≤ 1 second≤ 1 second

Max Peak-To-Peak ErrorMax Peak-To-Peak Error : - Large Meter Accuracy ( > 12” Nominal): - Large Meter Accuracy ( > 12” Nominal)

0.7% for 0.7% for qqtt ≤≤ q qii ≤≤ q qmaxmax

1.4% for q1.4% for qminmin ≤≤ q qii ≤≤ q qtt

- Small Meter Accuracy ( < 12” - Small Meter Accuracy ( < 12” Nominal)Nominal)

11% for % for qqtt ≤≤ q qii ≤≤ q qmaxmax

1.4% for q1.4% for qminmin ≤≤ q qii ≤≤ q qtt

Zero Flow ReadingZero Flow Reading : < 0.040 ft/s (12 mm/s) for each acoustic : < 0.040 ft/s (12 mm/s) for each acoustic

path.path.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 5.2 Pressure, Temperature and Gas Composition Influences 5.2 Pressure, Temperature and Gas Composition Influences

The Ultrasonic meter shall meet the accuracy on 5.1 over full The Ultrasonic meter shall meet the accuracy on 5.1 over full operating pressure, temperature and gas composition range operating pressure, temperature and gas composition range without the need for manual adjustment, unless otherwise stated without the need for manual adjustment, unless otherwise stated by the manufacturer.by the manufacturer.

If Ultrasonic meter requires manual input to characterize the If Ultrasonic meter requires manual input to characterize the flowing gas conditions (e.g gas density and viscosity), the flowing gas conditions (e.g gas density and viscosity), the manufacturer shall state the sensitivity of these parameter so that manufacturer shall state the sensitivity of these parameter so that the operator can determine the need to change these parameters the operator can determine the need to change these parameters as operating condition change. as operating condition change.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 6. Individual Meter Testing Requirements6. Individual Meter Testing RequirementsPrior to shipment, the manufacturer shall perform the following test and Prior to shipment, the manufacturer shall perform the following test and checks on each meter:checks on each meter:

6.1 Leakage Test6.1 Leakage TestAfter final assembly, the USM shall be leak-tested by manufacturer. The After final assembly, the USM shall be leak-tested by manufacturer. The test medium shall be inert gas, such as Nitrogen. The leak test pressure test medium shall be inert gas, such as Nitrogen. The leak test pressure shall be a minimum of 200 psig, maintained for a minimum of 15 shall be a minimum of 200 psig, maintained for a minimum of 15 minutes with no leak detectable with a non-corrosive liquid solution.minutes with no leak detectable with a non-corrosive liquid solution.

6.2 Dimensional Measurements6.2 Dimensional Measurements-Internal diameter of the meterInternal diameter of the meter-Length of each acoustic path between transducer faceLength of each acoustic path between transducer face-Axial distance between transducer pair.Axial distance between transducer pair.

6.3 Zero-Flow Verification Test6.3 Zero-Flow Verification TestTo verify the transit time measurement systems of the meter, the To verify the transit time measurement systems of the meter, the manufacture shall perform a Zero Flow verification test.manufacture shall perform a Zero Flow verification test.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 The zero flow test procedure shall be followed that includes the following The zero flow test procedure shall be followed that includes the following elements, at minimum:elements, at minimum:

a.a. After blind flange are attached to the end of the meter body, the meter After blind flange are attached to the end of the meter body, the meter shall be purged of all air and pressurized with a pure test gas or gas shall be purged of all air and pressurized with a pure test gas or gas mixture. The selection of test gas shall be the responsibility of the mixture. The selection of test gas shall be the responsibility of the manufacture. However, the acoustic properties of the test gas must be manufacture. However, the acoustic properties of the test gas must be well known and documented.well known and documented.

b.b. The gas pressure and temperature shall be allowed to stabilize at the The gas pressure and temperature shall be allowed to stabilize at the outset of the test. The gas velocities for each acoustic path shall be outset of the test. The gas velocities for each acoustic path shall be recorded for at least 30 seconds. The gas velocity and standard deviation recorded for at least 30 seconds. The gas velocity and standard deviation for each acoustic path then be calculated.for each acoustic path then be calculated.

c.c. Adjustment to the meter shall be made as necessary to bring the meter Adjustment to the meter shall be made as necessary to bring the meter performance into compliance with the manufacture’s specifications and performance into compliance with the manufacture’s specifications and specifications stated in this report.specifications stated in this report.

As part of the test procedure, the manufacture shall document the As part of the test procedure, the manufacture shall document the ultrasonic transducer serial numbers, and their relative locations in the ultrasonic transducer serial numbers, and their relative locations in the meter. The manufacture shall documented all the parameters used by the meter. The manufacture shall documented all the parameters used by the meter, e.g.: transducer/electronic transit-time delays, incremental timing meter, e.g.: transducer/electronic transit-time delays, incremental timing corrections, and all acoustic path lengths, angles, diameter and other corrections, and all acoustic path lengths, angles, diameter and other parameter used in the calculation of gas velocity for each acoustic path. parameter used in the calculation of gas velocity for each acoustic path. The manufacture shall note if the constants are dependent on specific The manufacture shall note if the constants are dependent on specific transducer pair.transducer pair.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 6.4 Flow Calibration Test6.4 Flow Calibration Test

If a flow calibration is performed, the following nominal test flow rates If a flow calibration is performed, the following nominal test flow rates are recommended, at a minimum: qare recommended, at a minimum: qminmin, 0.1 q, 0.1 qmaxmax, 0.25 q, 0.25 qmaxmax, 0.4 q, 0.4 qmaxmax, 0.7 , 0.7 qqmaxmax, and q, and qmaxmax..The designer may require that specific piping configuration and/or flow The designer may require that specific piping configuration and/or flow conditioners be used during flow calibration, understanding that conditioners be used during flow calibration, understanding that differences in upstream piping configurations may influence meter differences in upstream piping configurations may influence meter performance.performance.

6.4.1 Calibration Factor Adjusment6.4.1 Calibration Factor AdjusmentIf a meter is flow calibrated, the calibration factors should normally be If a meter is flow calibrated, the calibration factors should normally be applied to eliminate any indicated meter bias error. Some suggested applied to eliminate any indicated meter bias error. Some suggested methods of applying calibration factor are:methods of applying calibration factor are:

a.a. Using flow-weighted mean error (FWME) over the meter’s expected flow Using flow-weighted mean error (FWME) over the meter’s expected flow range.range.

b.b. Using a more sophisticated error correction scheme (e.g.: Multi-point or Using a more sophisticated error correction scheme (e.g.: Multi-point or polynominal algorithm, a piecewise linear interpolation method, etc) over polynominal algorithm, a piecewise linear interpolation method, etc) over the meter’s range of flow rates.the meter’s range of flow rates.

6.4.2 Test Report 6.4.2 Test Report The result of test required insection 6, shall be documented in a written The result of test required insection 6, shall be documented in a written report supplied to the designer or the operator by the manufacturer.report supplied to the designer or the operator by the manufacturer.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 For each meter the report shall include, at a minimum:For each meter the report shall include, at a minimum:

a. The name & address of the manufacturera. The name & address of the manufacturerb. The name & address of the test facilityb. The name & address of the test facilityc. The model & Serial Numberc. The model & Serial Numberd. The SPU firmware revision numberd. The SPU firmware revision numbere. The date of the teste. The date of the testf. The name & title of the person(s) who conducted the test.f. The name & title of the person(s) who conducted the test.g. A written description of the test proceduresg. A written description of the test proceduresh. The upstream & downstream piping configurationsh. The upstream & downstream piping configurationsi. A diagnostic report of the software configuration parametersi. A diagnostic report of the software configuration parametersj. All test data, including flow rates, pressures, temperatures, gas j. All test data, including flow rates, pressures, temperatures, gas composition and the measurement uncertainty of the test facility.composition and the measurement uncertainty of the test facility.k. A description of any variations or deviations from the required test k. A description of any variations or deviations from the required test conditions.conditions.

6.5 Quality Assurance6.5 Quality AssuranceThe manufacture shall establish and follow a written comprehensive The manufacture shall establish and follow a written comprehensive quality-assurance program for the assembly and testing of the meter quality-assurance program for the assembly and testing of the meter and its electronic system. and its electronic system.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 7. Installation Requirement7. Installation Requirement7.1 Environmental Consideration7.1 Environmental Consideration- Temperature- Temperature- Vibration- Vibration- Electrical Noise- Electrical Noise7.2 Piping Configuration7.2 Piping Configuration- - Flow DirectionFlow Direction- Piping InstallationPiping Installation

a. Recommend upstream & downstream piping configuration a. Recommend upstream & downstream piping configuration in minimum length, one without a flow conditioner and one in minimum length, one without a flow conditioner and one with a flow conditioner.with a flow conditioner.The recommendation should be supported by test dataThe recommendation should be supported by test datab. Specify the maximum allowable flow disturbance (e.g.: the b. Specify the maximum allowable flow disturbance (e.g.: the limits on swirl angle, velocity profile asymmetry, turbulence limits on swirl angle, velocity profile asymmetry, turbulence intensity, etc) intensity, etc)

- ProtrusionProtrusionChange in internal diameter and protrusion should be avoided. Change in internal diameter and protrusion should be avoided. The USM bore, Flanges & adjacent upstream pipe should all The USM bore, Flanges & adjacent upstream pipe should all have the same inside diameter, to within 1 % and be aligned have the same inside diameter, to within 1 % and be aligned carefully to minimize flow disturbance. carefully to minimize flow disturbance.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 - Internal SurfaceInternal Surface

The internal surface of the USM should be kept clean of any The internal surface of the USM should be kept clean of any deposits. If a layer of deposits accumulates inside USM, the deposits. If a layer of deposits accumulates inside USM, the cross-section area will be reduced, causing corresponding cross-section area will be reduced, causing corresponding increase in gas velocity and a positive measurement error.increase in gas velocity and a positive measurement error.

- ThermowellsThermowellsFor uni-directional flow, the designer should have the For uni-directional flow, the designer should have the thermowell installed downstream of the meter. The distance thermowell installed downstream of the meter. The distance from the dowstream flange face to the thermowell should be from the dowstream flange face to the thermowell should be between 2D and 5D.between 2D and 5D.The designer is cautioned that high gas velocities may cause The designer is cautioned that high gas velocities may cause flow-induced thermowell vibration.flow-induced thermowell vibration.

- Acoustic noise interferenceAcoustic noise interferenceSome pressure-reducing control valves, designed to reduce Some pressure-reducing control valves, designed to reduce audible noise, may produce very high level of ultrasonic noise audible noise, may produce very high level of ultrasonic noise under certain flowing condition. under certain flowing condition.

- Flow ConditionerFlow ConditionerFlow conditioner may or may not be necessary, depending on Flow conditioner may or may not be necessary, depending on the manufacturer’s meter design and the severity of any the manufacturer’s meter design and the severity of any upstream flow-profile disturbance. upstream flow-profile disturbance.

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 - Orientation of MeterOrientation of Meter

The designer should consult with the manufacturer to determine if The designer should consult with the manufacturer to determine if there is a preferred meter orientation for a given upstream piping there is a preferred meter orientation for a given upstream piping configuration.configuration.

- FiltrationFiltrationFiltration of the flowing gas is probably not necessary for most Filtration of the flowing gas is probably not necessary for most application of a USM. However accumulation of deposits should be application of a USM. However accumulation of deposits should be avoided.avoided.

7.3 Associated Flow Computer7.3 Associated Flow ComputerThe USM’s output is typically an uncorrected volume (actual volume The USM’s output is typically an uncorrected volume (actual volume at line condition). Therefore, an associated flow computer or corrector at line condition). Therefore, an associated flow computer or corrector must be installed by the designer to correct the volume rate and must be installed by the designer to correct the volume rate and accumulated volume for pressure, temperature and compressibility.accumulated volume for pressure, temperature and compressibility.

7.3.1 7.3.1 Flow Computer CalculationFlow Computer CalculationThe necessary calculations are similar to the equations described in The necessary calculations are similar to the equations described in AGA 7, and are summarized in the following expression:AGA 7, and are summarized in the following expression:

)/).(/).(/.( ZfZbTfTbPbPfQfQb

AGA REPORT NO. 9 1998AGA REPORT NO. 9 1998 7.4 Maintenance7.4 Maintenance

The operator should follow the manufacturer’s recommendations The operator should follow the manufacturer’s recommendations for maintenance. Periodic maintenance could be as simple as for maintenance. Periodic maintenance could be as simple as monitoring several CPU diagnostic measurement, such as: signal monitoring several CPU diagnostic measurement, such as: signal quality, speed of sound for each acoustic pathquality, speed of sound for each acoustic path

8. Field Verification Test8. Field Verification TestThe manufacturer should provide a written field verification test The manufacturer should provide a written field verification test procedure to the operator that will allow the USM to be procedure to the operator that will allow the USM to be functionally tested to ensure that the meter is operating properly. functionally tested to ensure that the meter is operating properly.