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GB/T 18604-2014 PDF in English

GB/T 18604-2014 (GB/T18604-2014, GBT 18604-2014, GBT18604-2014)
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GB/T 18604-2014: PDF in English (GBT 18604-2014)

GB/T 18604-2014
ICS 75.180.30
E 98
Replacing GB/T 18604-2001
Measurement of natural gas flow by gas ultrasonic
flow meters
Issued by: General Administration of Quality Supervision, Inspection and
Standardization Administration of the People's Republic of
Table of Contents
Foreword ... 4 
1 Scope ... 6 
2 Normative references ... 6 
3 Measurements, terms and definitions ... 7 
4 Measurement principle ... 10 
4.1 Fundamental principle ... 10 
4.2 Influencing factors of accuracy measurement ... 11 
5 Working conditions ... 11 
5.1 Natural gas quality ... 11 
5.2 Pressure ... 12 
5.3 Temperature ... 12 
5.4 Flow range and flow direction ... 12 
5.5 Velocity distribution ... 12 
6 Measurement performance requirements ... 13 
6.1 Measurement performance requirements for multi-path gas ultrasonic flow meter ... 13 
6.2 Measurement performance requirements for single-path gas ultrasonic flow meter ... 16 
6.3 Influence of working conditions on measurement performance ... 16 
7 Flow meter requirements ... 16 
7.1 Composition and basic provisions ... 16 
7.2 Meter body ... 17 
7.3 Ultrasonic transducer ... 19 
7.4 Electronic components ... 20 
7.5 Flow computer ... 22 
8 Installation requirements and maintenance ... 24 
8.1 Installation influencing factors ... 24 
8.2 Pipe configuration ... 25 
8.3 Maintenance ... 27 
9 Testing requirements for on-site verification ... 28 
9.1 Testing contents and steps ... 28 
9.2 Testing report ... 28 
10 Flow calculation method and estimation of measurement uncertainty ... 29 
10.1 Flow calculation under standard reference conditions ... 29 
10.2 Determination of measured flow value under standard reference conditions... 31 
10.3 Flow calculation under working conditions ... 31 
10.4 Estimation of flow measurement uncertainty ... 31 
Annex A (informative) Fundamental principles ... 35 
Annex B (normative) Flow calibration of flow meter components ... 46 
Annex C (normative) Exit-factory testing requirements ... 53 
Annex D (informative) Documents available ... 56 
Annex E (informative) Generation and prevention measures of acoustic noise
... 59 
Annex F (informative) Performance verification tests of flow meter and flow
conditioner ... 65 
Annex G (informative) Monitoring and guarantee of on-site measurement
performance of flow meter ... 67 
This Standard was drafted in accordance with the rules given in GB/T 1.1-2009.
This Standard replaces GB/T 18604-2001 “Measurement of natural gas flow by
ultrasonic flow meter”. Compared with GB/T 18604-2001, in addition to editorial
modifications, main technical changes as follows:
- added three terms: maximum error shift with one path failed, speed of
sound (SOS) deviation and metering package (see 3.2.17, 3.2.18 and
- modified influencing factors of measurement accuracy; divided the
influencing factors into two categories: internal factors and external factors
(see Clause 4);
- further specified the range of working temperature as medium temperature
and ambient temperature (see 5.3);
- improved the requirements for zero-flow reading of multi-path gas ultrasonic
flow meter; added two technical requirements of sound velocity deviation
and maximum sound velocity difference; modified the maximum peak-to-
peak error requirement above the demarcation flow (see 6.1);
- added that according to the ambient conditions and working conditions,
taking necessary thermal insulation, anti-freeze measures, and related
requirements for acoustic noise and pulsation to flow meter components
(including upstream and downstream straight pipe sections, flow meters
and flow conditioners, temperature tapping holes and sampling holes)
(see 8.1.1, 8.1.4, 8.1.5 and Annex E);
- modified relevant requirements for pipe installation upstream straight pipe
section and flow conditioner installation position, temperature
measurement hole and sampling hole insertion depth, flow conditioner
(see 8.2.2, 8.2.5 and 8.2.7 and Annex F);
- added the requirements for on-site measurement performance of ultrasonic
flow meters in routine maintenance (see 8.3.1 and Annex G);
- added the requirements that theoretical sound velocity is calculated
according to the method provided by AGA Report No.10 “Speed of sound
in natural gas and other related hydrocarbon gases” and other methods
that are same as the calculation (see 9.1.3);
- added the calculation method and uncertainty estimation for mass flow and
energy flow (see Clause 10);
- modified flow calibration to flow calibration of metering package; modified
stability requirements for temperature and pressure, test traffic point (see
B.2.2 and B.3.3);
- deleted the original Annex E “Upper and lower pipe length requirements”;
- added technical requirements of “acoustic noise generation and prevention
measures” (see Annex E);
- added technical requirements of “flow meter and flow conditioner
performance verification test” (see Annex F);
- added technical requirements of “monitoring and guarantee of flow meter
on-site measurement performance” (see Annex G).
This Standard uses redrafting method to modify and adopt AGA Report No.10
“Speed of sound in natural gas and other related hydrocarbon gases”.
This Standard was proposed by and shall be under the jurisdiction of National
Technical Committee on Petroleum Gas of Standardization Administration of
China (SAC/TC 355).
The drafting organizations of this Standard: National Oil and Gas Large Flow
Metering Station Chengdu Sub-Station, PetroChina Southwest Oil and Gas
Field Branch, PetroChina Group Engineering Design Co., Ltd. Southwest
Main drafters of this Standard: Duan Jiqin, He Min, Wen Dailong, Ren Gui,
Huang He, Liu Yongming, Chen Huiyu, Wang Qiang, Chen Qi, Ni Rui.
Measurement of natural gas flow by gas ultrasonic
flow meters
1 Scope
This Standard specifies measurement performance requirements of gas
ultrasonic flow meters, meter body requirements, installation and maintenance,
field verification test requirements, and flow calculation methods and
measurement uncertainty estimates.
This Standard is applicable to gas ultrasonic flow meters of plug-in transit-time
difference method (hereinafter referred to as the flow meter), which are
generally used for natural gas flow measurement in gathering devices, gas
pipelines, storage facilities, gas distribution systems and customer metering
systems. The use of external clamp-on gas ultrasonic flow meter can refer to
this Standard.
2 Normative references
The following referenced documents are indispensable for the application of
this document. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any
amendments) applies.
GB 3836.1, Explosive atmospheres - Part 1: Equipment - General
GB 3836.2, Explosive atmospheres - Part 2: Equipment protection by
flameproof enclosures “d”
GB 3836.4, Explosive atmospheres - Part 4: Equipment protection by
intrinsic safety “i”
GB/T 4208, Degrees of protection provided by enclosure (IP code) (IEC
GB/T 11062-1998, Natural gas - Calculation of calorific values, density,
relative density and Wobbe index from composition
GB/T 13610, Analysis of natural gas by gas chromatography
GB/T 17747 (all parts), Natural gas - Calculation of compression factor
GB/T 21446-2008, Measurement of natural gas flow by means of standard
orifice meter
SY/T 0599-2006, Metallic material requirements - Resistance to sulfide
stress cracking and stress corrosion cracking for gas surface equipment
JJG 1030-2007, Verification Regulation of Ultrasonic Flowmeters
ISO 5167-1:2003, Measurement of fluid flow by means of pressure
differential devices inserted in circular cross-section conduits running full -
Part 1: General principles and requirements
AGA Report No.10, Speed of sound in natural gas and other related
hydrocarbon gases
3 Measurements, terms and definitions
3.1 Measurements
See Table 1 for the measurements, names and symbols of unit used in this
Table 1 -- Measurements and names as well as symbols of unit
Symbol of
measurement Name of measurement
dimension Symbol of unit
D Inner diameter of flow meter L m
kc Velocity distribution correction 1
L Path length L m
P Static pressure ML-1T-2 Pa
qv Volumetric flowrate L3T-1 m3/s
qm Mass flowrate MT-1 Kg/s
qe Energy flowrate L3T-1 J/s
qt Transition flowrate L3T-1 m3/h
Volume accumulation over a period
of time under standard reference
L3 M3
T Airflow thermodynamic temperature K
t Time T s
V Mean axial fluid velocity LT-1 m/s
Average flow velocity along acoustic
path LT
-1 m/s
X Axial distance L m
Z Compression factor 1
φ Path angle 1 rad
NOTE 1: In the measurement dimension, symbol L refers to length, symbol T refers to time, symbol
M refers to mass and symbol refers to thermodynamic temperature.
NOTE 2: The symbols not listed in the table are explained in the text.
3.2 Terms and definitions
The following terms and definitions apply to this document.
3.2.1 transit-time difference method
A gas flow measurement method that within the same stroke in the flowing gas,
using the transit-time difference of two ultrasonic signals of downstream and
upstream transits to determine the average flow velocity along acoustic path.
3.2.2 ultrasonic transducer
A component that converts acoustic energy to electrical signal and vice versa.
Generally, it is installed in a pair and the pair work simultaneously.
3.2.3 signal processing unit
A part of flow meter, consisting of electronic components and microprocessor
3.2.4 meter body
A pipe section where the gas to be tested passes, where components such as
ultrasonic transducer and pressure measuring connector are installed, that is
manufactured in a special way to comply with relevant regulations in any aspect.
3.2.5 acoustic path
The actual path of the ultrasound signal between a pair of transmitting and
receiving ultrasound transducers.
3.2.6 path length; L
The distance between the end faces of a pair of ultrasonic transducers (see
Figure 1).
3.2.7 axial distance; X
The projection length of path length on the parallel line of pipe axis (see Figure
Figure 1 -- Simplified geometric relationship diagram of plug-in gas
ultrasonic flow measurement
3.2.8 path angle; φ
The angle between acoustic path and pipe axis (see Figure 1).
3.2.9 average flow velocity along acoustic path;
Gas flow velocity in a plane that is determined by acoustic path and flow
3.2.10 mean axial fluid velocity; V
Ratio of flowrate to measured cross-sectional area.
3.2.11 velocity distribution correction; kc
Ratio of mean axial fluid velocity to average flow velocity along acoustic path.
3.2.12 velocity sampling interval
Time interval between two adjacent gas flow measurements by a pair of
ultrasonic transducers or acoustic paths.
3.2.13 zero-flow reading
The reading of the maximum permissible flow rate when gas is in a state of rest.
3.2.14 transition flow rate; qt
The flow value between the maximum flow and the minimum flow. It divides the
flow range into two zones with different tolerances, that is, “high zone” and “low
zone” (see Figure 2).
3.2.15 maximum peak-to-peak error
The difference between the upper limit maximum error point and the lower limit
maximum error point (see Figure 2).
3.2.16 flow calibration factor
Flow meter coefficient that to conduct flow calibration on the flow meter and
correct the test results according to a certain correction method, hereinafter
referred to as the calibration factor.
3.2.17 maximum error shift with one path failed
At the same flow, the maximum difference BETWEEN the measurement error
when all acoustic paths work AND the measurement error when one acoustic
path fails.
3.2.18 speed of sound (SOS) deviation
The maximum relative deviation between average sound velocity obtained by
the measurement of flow meter and theoretical sound velocity in the gas.
3.2.19 metering package
The component that consists of a flow meter, supporting upstream and
downstream straight pipe sections, temperature measuring hole, pressure
obtaining hole as well as flow conditioner.
4 Measurement principle
4.1 Fundamental principle
The gas ultrasonic flow meter of transit-time difference method is a velocity flow
meter that measures high frequency sound pulse transit-time to obtain gas flow.
The transit time is measured by the acoustic pulses that are transmitted and
received between pairs of transducers outside the pipe or within the pipe. The
acoustic pulse transits along the diagonal direction (see Figure 1). Acoustic
pulses transmitted downstream are accelerated by airflow while acoustic pulses
transmitted in reverse flow shall be decelerated. The transit-time difference is
related to the mean axial fluid velocity. Use numerical calculation technique to
calculate the mean axial fluid velocity and the flow that pass through the gas
ultrasonic flow meter under working conditions. The flow meter that only has
one acoustic path is called single-path gas ultrasonic flow meter. The flow meter
that has two or more acoustic paths is called multi-path gas ultrasonic flow
meter. When the ultrasonic transducer is in direct contact with the gas, it is
called plug-in. When the ultrasonic transducer is not in direct contact with the
gas, it is called external clamp-on.
See Annex A for more details.
4.2 Influencing factors of accuracy measurement
4.2.1 Internal factors include:
a) Geometric size of meter body as well as accuracy and stability of
ultrasonic transducer’s position parameters;
b) Quality and accuracy of ultrasonic transducer and electronic components
used for transit-time measurement (including electronic clock stability);
c) Sampling period and integral calculation method used for transit-time
testing and average flow rate calculation;
d) Calibration (including compensation for electronic component and
ultrasonic transducer signal lag).
4.2.2 External factors include:
a) Airflow velocity distribution;
b) Temperature gradient;
c) Airflow pulsation;
d) Acoustic and electromagnetic noise;
e) Solid and liquid depositions;
f) Geometric size changes over time.
5 Working conditions
5.1 Natural gas quality
The natural gas components measured by the flow meter are generally within
the scope specified in GB/T 17747 (all parts). The relative density of the natural
gas is 0.55~0.80.
In one of the following cases, it shall consult the manufacturer for the material
of the flow meter, the type of the ultrasonic transducer as well as whether the
measuring accuracy of the flow meter meets the requirements:
a) CO2 content exceeds 10%;
b) Work under conditions that are close to the critical density of natural gas
c) Total sulfur content exceeds 460mg/m3, including mercaptans, hydrogen
sulfide and elemental sulfur.
Under normal gas delivery conditions, the attachments (such as condensate or
oil residue with processing impurities, ash and sand, etc.) inside the meter body
shall reduce the flow area of the flow meter, which shall affect the measurement
accuracy. Meanwhile, the attachments shall also obstruct or attenuate the
ultrasonic transducer to emit and receive ultrasonic signals OR affect the
reflection of ultrasonic signals on the inner wall of the meter body. Therefore, it
shall regularly check and clean the flow meter.
5.2 Pressure
The ultrasonic transducer has certain requirements for gas minimum density (it
is the function of pressure). The minimum working pressure shall ensure that
the acoustic pulse can transit normally in natural gas.
5.3 Temperature
The manufacturer shall, according to the actual working condition requirements
of the user, provide a flow meter that meets temperature range requirements.
The working medium temperature of the flow meter is -20°C~60°C; the working
environment temperature range is -40°C~60°C.
5.4 Flow range and flow direction
The flow measurement range of the flow meter is determined by the actual flow
rate of gas. The typical flow rate of the measured natural gas is generally 0.3m/s
~ 30m/s. The user shall verify that the measured gas flow rate is within the flow
range specified by the manufacturer. The corresponding measurement
accuracy shall be in accordance with the provisions of Clause 6.
The flow meter has the ability to measure in both directions. The bidirectional
measurements have the same accuracy. The user shall indicate if bidirectional
measurement is required, so that the manufacturer can properly configure the
signal processing unit parameters.
5.5 Velocity distribution
Under ideal conditions, the natural gas flow that goes into the flow meter shall
be in symmetrically and fully-developed turbulent velocity distribution. The
configuration of upstream pipe (i.e., various upstream pipe fitting, pressure
regulator and length of straight section) shall influence the velocity profile of the
gas that goes into the flow meter, so as to affect measurement accuracy. The
size of the influence and whether the influence is positive or negative are related
to the compensation capability of the flow meter to a certain extent.
6 Measurement performance requirements
This clause specifies that the flow meter shall meet a set of minimum
measurement performance requirements. Before the adjustment of flow
calibration factor, the flow meter shall meet the requirements for those
performances, so as to ensure that the problems and defects of the flow meter
are not covered due to the adjustment of flow calibration factor.
The user shall, according to the provisions of Clause 7 and Annex B, require
inspection and flow calibration to the flow meter. It shall also follow the
installation requirements in Clause 8 to ensure that the measurement accuracy
of the flow meter is improved based on meeting the minimum performance
For the flow meter of each size, the manufacturer shall specify the flow
threshold, that is, minimum flowrate qmin, transition flowrate qt and maximum
flowrate qmax. No matter whether it has been subject to flow calibration, within
the flow range specified by the manufacturer, the flow meter shall meet the
measurement performance requirements of this clause.
6.1 Measurement performance requirements for multi-path gas
ultrasonic flow meter
6.1.1 General
Before any adjustment of flow calibration factor, the general measurement
performance of all multi-path gas ultrasonic flow meters shall be able to meet
the following requirements:
a) Repeatability:
0.2%, qt ≤ q ≤ qmax;
0.4%, qmin ≤ q < qt;
NOTE: q is the flow to be measured, same as follows.
b) Resolution: 0.001m/s;
c) Velocity sampling interval: ≤1s;
d) Zero-flow reading: < 6mm/s for each acoustic path;
e) Speed of sound (SOS) deviation: ±0.2%;
f) Maximum speed of sound (SOS) difference between each acoustic path:
6.1.2 Accuracy of large-diameter flow meter
Before any adjustment of flow calibration factor, the multi-path gas ultrasonic
flow meter of which the diameter is equal to or greater than 300mm shall meet
the following requirements for measurement accuracy (see Figure 2):
a) Maximum error:
±0.7%, qt ≤ q ≤ qmax;
±1.4%, qmin ≤ q < qt;
b) Maximum peak-to-peak error:
0.7%, qt ≤ q ≤ qmax;
1.4%, qmin ≤ q < qt.
6.1.3 Accuracy of small-diameter flow meter
Before any adjustment of flow calibration factor, the multi-path gas ultrasonic
flow meter of which the diameter is less than 300mm shall meet the following
requirements for measurement accuracy (see Figure 2):
a) Maximum error:
±1.0%, qt ≤ q ≤ qmax;
±1.4%, qmin ≤ q < qt;
b) Maximum peak-to-peak error:
1.0%, qt ≤ q ≤ qmax;
1.4%, qmin ≤ q < qt.
NOTE: When the path length is short, it is difficult to measure the transit-time of acoustic wave in
turbulent gas. Therefore, the requirements for the small-diameter flow meter are low.
Figure 2 -- Summary of measurement performance requirements for multi-path gas ultrasonic flow meter
Zero-flow reading < 6mm/s (for each acoustic path)
calibration curve of
flow meter
Large-diameter flow meter (≥12’’)
Maximum peak-to-peak error=0.7% (qj≥qt) Small-diameter flow meter (< 12’’)
Maximum peak-to-peak error=1.0% (qj≥qt)
Maximum peak-to-peak error=1.4% (qj< qt)
error limit
Error limit of small-
diameter flow meter
Error limit of large-
diameter flow meter
Error limit of large-
diameter flow meter
Error limit of small-
diameter flow meter
error limit
Flow / qi
6.2 Measurement performance requirements for single-path gas
ultrasonic flow meter
The measurement performance requirements for single-path gas ultrasonic
flow meter may be lower than the measurement performance requirements for
multi-path gas ultrasonic flow meter. The specific indicators are provided by the
6.3 Influence of working conditions on measurement performance
Under the working conditions specified in Clause 5, the flow meter shall meet
the measurement performance requirements specified in 6.1 and 6.2 without
any manual adjustment. If the manual input of physical parameters is required
to determine the physical parameters (such as density and viscosity) under
natural gas flow conditions, the manufacturer shall give the sensitivity degree
that the flow meter is affected by those parameters, so that when the working
conditions are changed, the user can determine whether the influence brought
by those changes is acceptable.
7 Flow meter requirements
7.1 Composition and basic provisions
7.1.1 Composition
The flow meter mainly consists of the following two parts:
a) meter body, ultrasonic transducer and its mounting parts;
b) signal processing unit (SPU) that is composed of electronic components
and microprocessor system. It receives ultrasonic transducer signals and
has functions such as processing measurement signals and displaying,
outputting and recording measurement results. The electrical signal
processing and conversing part located in the field is installed in the
7.1.2 Basic provisions
Use the materials that are suitable for working conditions of the flow meter to
design and manufacture the meter body and all other parts, including pressure
members and external electronic components, in accordance with the process
requirements for the metering system where they are. If the user has special
requirements, it shall comply with the appropriate specifications or regulations
applicable to each specific installation condition specified by the user.
Before the flow meter exits the factory, the manufacturer shall conduct exit-
factory testing and provide the exit-factory testing report to the user. See Annex
C for the exit-factory testing requirements. There shall be corresponding
documents, see Annex D.
7.2 Meter body
7.2.1 Maximum working pressure
The maximum designed working pressure of the flow meter shall be the
minimum among the maximum working pressures of the following components:
meter body, flange, ultrasonic transducer components and their mounting
The connecting flange of the meter body shall comply with general industrial
standards, national or international standards.
7.2.2 Corrosion resistance requirements
All components of the flow meter that are in contact with the medium shall be
made of the materials that are suitable for natural gas. The materials used for
the flow mater that contains corrosive mediums such as H2S and CO2 shall
comply with the provisions of SY/T 0599.
All external parts of the flow meter shall be made of corrosion resistant materials.
Or use corrosion resistant coating that is suitable to use in a typical atmospheric
environment of the natural gas industry.
7.2.3 Ability of adapting to environment
The shell, nameplate of the flow meter and each component shall comply with
the provisions of GB/T 4208, at least meeting the level requirements of IP65.
7.2.4 Length and nominal diameter
The manufacturer shall give the standard length of the meter body of each
pressure level and nominal diameter. In order to match existing pipes, the user
can specify different lengths and nominal diameters.
7.2.5 Ultrasonic transducer port
Natural gas may contain impurities (such as condensate or dust). The designed
ultrasonic transducer port shall minimize the possibility of liquids or solids
staying on them. According to user’s requirements, a valve may be provided so
that the ultrasonic transducer can be replaced with internal pressure in the
meter body.
7.2.6 Pressure obtaining hole
There shall be at least one pressure obtaining hole on the meter body to
measure the static pressure. The nominal diameter of each pressure obtaining
hole shall be within 4mm~10mm. If the wall thickness of meter body is less than
20mm, the nominal diameter of the pressure obtaining hole shall be 4mm. And
from the inner wall of meter body, at least within the length 2.5 times the
diameter of pressure obtaining hole, it is cylindrical; and the axis of the pressure
obtaining hole shall be perpendicular to the measuring tube axis. The edges of
pressure obtaining hole of inner wall of meter body shall be right angle, without
burrs and curls.
Each pressure obtaining hole shall have internal thread that can be equipped
with isolation valve and swing space where it can directly mount the isolation
valve on the pressure obtaining hole. The specification of the internal thread is
better to be 1/4" NPTF or 1/2" NPTF. The pressure obtaining hole shall be set
at the top, left or right of meter body. When necessary, the pressure obtaining
hole can be added, so as to provide the flexibility to install pressure transmitter
to the user, be conducive to maintenance and discharge the condensate in the
pressure transmitter pressure tube back into the meter body.
7.2.7 Flow meter markings
A nameplate that contains the following information shall be set on the flow
a) Manufacturer’s name, flow meter model, serial number and date of
b) Nominal pressure and total mass;
c) Nominal diameter and inner diameter;
d) Highest and lowest storage temperature;
e) Working pressure and temperature range;
f) Maximum and minimum hourly flow under working state;
g) Positive direction of gas flow;
h) Explosion-proof level.
For easy identification, each ultrasonic transducer port shall be marked with a
permanent unique mark. If a stamp mark on the meter body, it shall use low
stress stamping form, i.e., round bottom print.
7.2.8 Appearance quality requirements
The appearance quality requirements include:
a) The appearance of the flow meter shall be neat and beautiful. The surface
shall be well treated. There shall be no burrs, nicks, cracks, rust, mildew
and peeling;
b) All words and symbols shall be clear;
c) The sealing surface shall be smooth and not damaged.
7.2.9 Other requirements
The flow meter shall be designed that when it is placed on a smooth surface
with a slope of 10%, it shall not roll, so as to prevent that, during installation or
maintenance period, when it is placed on the ground temporarily, it shall
damage the exerted ultrasonic transducer and signal processing unit.
The flow meter shall be also designed as that it shall be easily moved during
transportation and installation period. It shall be also designed to have space
for hanging holes and slings.
The user can request the manufacturer to provide the locating pin on the
upstream and downstream flanges of the flow meter, so as to ensure the correct
positioning of the flow meter’s on-site installation.
7.3 Ultrasonic transducer
7.3.1 Technical requirements
The manufacturer shall give general technical indicators of ultrasonic
transducer, such as key dimensions, maximum permissible working pressure,
range of working pressure, range of working temperature and gas composition
The manufacturer......
Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.