1.  CODES AND REQUIREMENTS
 The ultrasonic meter body and all other parts,
including the pressure-containing structure,
and external electronic components shall be
designed and constructed of materials
suitable for the service conditions for which
the meter is rated and in accordance with any
codes and regulations applicable to each
specific meter installation, as specified by the
designer.

2.  The manufacturer shall establish and follow a
written comprehensive quality-assurance
program for production, assembly and
testing of the meter and its electronic
assembly (ISO 9000, API specificationQ1,
etc).
 The inspector should have the quality
assurance program.

3.  Meter pipeline flange classes:ANSI class 150,
300, 600, 900 etc.
 The maximum design operating pressure of
the meter should be lowest of the maximum
design operating pressure of the following;
 Meter body, Flanges,Transducer
connections,Transducer assemblies.

4.  The above shall be obtained in-line with the
applicable codes for the jurisdiction in which
the meter will be operated as well as the
specified environmental temperature range.
 The designer should provide the
manufacturer with information on all
applicable codes for the installation site and
any other requirements specific to the
operator.

5.  All the meter parts that are exposed to
flowing fluid wet shall be compatible with
natural gas and related fluids.
 All the external parts of the meter should be
made non-corrosive materials or sealed with
a corrosive resistant coating suitable for use
in the atmosphere typically found in the
natural gas industry and/or as specified by the
designer

6.  The manufacturer’s publication of the
standard for overall face-to-face length of the
meter body with flanges class and diameter.
 The Ultrasonic meter bore and adjacent
upstream pipe along with flanges should have
the same inside diameter to 1% of each other
 Both ends of the Ultrasonic meter is referred
as “upstream” i.e. bi-directional

7.  UM acoustic transducer port should be
designed in a way that it should not trap or
accumulate debris as natural gas could flow
with impurities.
 To avoid depressurizing the meter during
change of a failed transducer, the meter
should be equipped with valves and
necessary additional devices mounted on the
transducers for easy replacement.

8.  There should be at least one pressure tap
provide for measuring static pressure.
 Tap hole size: Between 1/8” and 3/8” nominal
diameter and cylindrical over a length at least
2.5 times the diameter of the tapping,
measured from the inner wall of the meter
body.

9.  Ergonomics such as human engineering,
biotechnology and human factor plays a vital
role in the design of UM to suit usable and to
pose in stable position when kept on a 10%
slope.This prevents damage of protruding
transducer and SPU when the UM is
temporary kept on the ground during
maintenance and installations.

10.  A name and plate affixed on the meter body
should contain the following;
 The manufacturer, model number, serial
number, month and year manufactured.Then
the meters specifications and operational
properties.
 Transducers should be marked with a unique
designation permanently for easy reference.

11.  SPECIFICATIONS.
 The manufacturer shall state the general
specifications of the UM transducers such as;
 Critical dimensions, maximum and minimum
allowable operating pressure as well range,
temperature range, gas composition
limitations
 The UM size and expected operating
conditions and others should be tagged on the
UM to alert the operator’s field personnel.

12.  Sudden depressurization of a UM can cause a
damage if trapped volume of gas expands
inside the transducer.
TRANSDUCER EXCHANGE
 Replace or relocation of transducers shall be
possible without a significant change in
meter performance.

13.  The pair of transducers shall be subjected to test by
the manufacturer and documented as part of UM’s
quality assurance program.
ELECTRONICS
 The UM electronic system unit which includes;
 Power supply, micro computer, signal processing
components and UM excitation circuits etc, all
referred to as SPU shall be housed in an enclosure
close proximity to the meter.
 The manufacturer shall make a unique identification
of the circuit board and the UM shall operate within
the manufacturers specification for AC/DC supply.

14.  The SPU should be equipped with at least one of the
following output;
 Serial data interface e.g. Rs-232, Rs-485 or equivalent.
 Frequency, representing flow rate at line conditions
 Analog current loop(4-20MA,DC) output scaled for
flow rate at the line conditions.
NOTE:
 Flow rate signal should be scaled up to 120% of the
meter’s maximum flow rate, Qmax
 A low flow rate cut off function should be installed for
the purpose to set the flow rate to zero when the
indicated flow rate is below the minimum value.

15.  Again there should be a provision option that allows
the user, a selection to make the flow rate output go
either zero, maximum meter flow rate, or a user
selected value, when the maximum meter capacity is
exceeded.
 Two separate flow rate outputs and a directional state
output or serial data values should be provided for bi-
directional applications to facilitate the separate
accumulation volumes.
 All output should be isolated properly from the
ground and should have the necessary voltage
protection to meet the electronics design testing
requirements.

16.  The design of the UM, including SPU, should be analyzed,
tested and certified by an applicable laboratory, and then
each meter should be labeled as approved for operation in
National Electricity code class 1, Division 2, Group D,
Hazardous Area, at a minimum.
 Safety designs and explosion-proof enclosure designs are
generally certified and labeled for Division 1 locations.The
designer may specify the more sever Division 1 location
requirement to achieve a more conservative installation
design.
 Cable jackets, rubber, plastic and other exposed parts shall
be resistant to ultraviolet light, heat, oil and grease.

17.  The easiness and ability to replace or relocate transducers,
cables, electronic parts and software without a significant
change/alteration of the meter performance is a
requirement.There should be a proven procedures for the
user and sufficient data to demonstrate the above.
 NOTE: Changing of any of these components without re-
calibration may lead to additional measurement
uncertainty.The operator should maintain a set of normal
reference data.
 When components are replaced, the operator should
compare the indicated path relationships, velocity ratios,
SOS ratios etc, to the reference data.The previous
function should be compared with the post-replacement
condition.

18.  FIRMWARES:
 The computer codes responsible for the control,
operation flow calculation constants and
operator entered parameters, of the meter
should be stored in a non-volatile memory.
 All the flow calculation constants and
parameters should be possibly verified for
auditing purposes.This should take place while
the meter is in operation.
 The manufacturer should also maintain a record
of all firm ware revision.

19.  The firmware revision number, revision date,
serial number and/or checksum should be either
made available to the auditor by visual
inspection of the marking on the firmware chip
or capable of being displayed by the meter or
ancillary device
 The manufacturer may offer firmware upgrades
from time to time to improve the performance
of the meter or add additional features.
 The manufacturer shall notify the operator of
the firmware revision will effect the accuracy of
a flow-calibrated meter.

20.  This implies the supply of a capability for local or
remote configuring of the SPU and for
monitoring the meter operation.
 As a minimum, the software should be able to
display and record the following measurement
 Flow rate at line conditions, mean velocity,
average speed of sound, speed of sound along
each acoustic path and ultrasonic acoustic signal
quality received by each transducer.

21.  It should be possible for the auditor or the
inspector to view and print the flow
measurement configuration parameters used by
the SPU, e.g.. Calibration constants, meter
dimensions, time averaging periods and
sampling rate.
 This helps to dictate accidental or undetectable
alteration of those parameters that affects the
meter performance.
 Suitable provisions includes; a sealable switch or
jumper, a permanent programmable read-only-
memory chip or a password in the SPU.

22.  It should be possible for the auditor to verify all
algorithms, constants and configuration parameters being
used in any specific meter, are producing the same or
better performance as when the meter design was
originally flow tested or the particular meter was last flow-
calibrated and any calibration factors were changed.
 The auditor may have rely on the manufacturer for portion
of this verification because of the proprietary or initiation
of some UM algorithms.
 NOTE: Generally as stated above, the metering system
should conform to the requirements provided in API
Manual of Petroleum Measurement Standards(MPMS)
chapter 21.1 for electronic gas measurement.

23.  There should be a provision of alarm-status
outputs in the form of fail-safety relay contacts
or voltage solid-state switches isolated from
ground;
 Output invalid:When the indicated flow rate at
line condition is invalid.
 Trouble: when any of several monitored
parameter fall outside of normal operation for a
significant period of time.
 Partial failure:When one or more of the multiple
ultrasonic path results is not usable.

24.  The manufacturer should make available the
following and other diagnostic
measurements through a data interface .e.g.
Rs-232, Rs-485 etc.
 PathAGC levels
 Path transit time
 Average axial flow velocity through the meter
 Flow velocity for acoustic path(or equivalent
for evaluation of the flowing velocity profile)
 Speed of sound along each acoustic path

25.  Average speed of sound
 Velocity sampling interval
 Averaging time interval
 Percentage of accepted pulsed for each
acoustic path
 Status and/or measurement quality
indicators
 Alarm and failure indicators.

26.  There should be a report documentation on
accuracy, installation effects, electronic,
ultrasonic transducers and zero-flow
verification.
 The manufacturer should also provide all
necessary certificates and documentation for
a correct configuration, set-up and use of the
particular meter so that it operates correctly.

27.  The manufacturer, for analysis purpose
should furnish specific meter outline
drawings, including overall flange face-to-
face dimensions, inside diameter,
maintenance space clearances, conduit
connection points, estimated weight, and
other meter-specific details as required by
the designer.

28.  Before the shipment of the meter, the
following should be provide by the
manufacturer for the inspector review;
 Metallurgical reports
 Weld inspection reports
 Pressure test reports and
 Final dimensional measurements.

29.  The part specifies a set of minimum measurement
performance requirements that the ultrasonic meters
must meet.
 It is recommended that Ums be flow-calibrated so to
improve measurement accuracy beyond the minimum
performance requirements.
 When a meter is flow-calibrated, it shall meet the
minimum measurement performance requirements
before the application of any calibration-factor
adjustment.
 The amount of calibration-factor adjustment, for the
meter only, shall be within the error limits stated in these
performance requirement.This is to ensure that the major
flaw in the meter is not masked by large calibration factor.

30.  For custody transfer, UM should be flow
calibrated
 Calibration factor adjustments are made to
minimize a meter’s measurement bias error.
 The designer should follow carefully installation
recommendations as it is known that any
installation effects may lead add to the overall
measurement uncertainty.
 The manufacturer shall specify, for each meter-
design and size, flow-rate limits for each meter
design, for Qmin, Qt and Qmax.

31.  Prior to any calibration-factor adjustment, the
general flow-measurement performance of all
Ums shall meet the following requirements;
 Repeatability ………………: ±0.2% for qt ≤ qi ≤ qmax
±0.4% for qmin ≤ qi ˂ qt
 Resolution …………………...: 0.003ft/s (0.001m/s)
 Velocity sampling interval: ≤ 1second
 Zero flow-reading ………….: ˂ 0.020ft/s(6mm/s)
for each acoustic
path
 Speed of sound deviation .: ± 0.2%
 Maximum SOS path spread .: 1.5 fps(0.5m/s)

32.  Ums of 12-inch (nominal) diameter size and
lager shall meet the measurement accuracy
requirements, prior to making any
calibration-factor adjustment;
 Maximum error………: ± 0.7% for qt ≤ qi ≤ qmax
± 1.4% for qmin ≤ qi ˂ qt
 Maximum peak-to peak error:
………………………………..: 0.7% for qt ≤ qi ≤ qmax
1.4% for qmin ≤ qi ˂ qt

33.  The following measurement accuracy is
required prior to any calibration-factor
adjustment;
 Maximum error ………….: ± 0.1% for qt ≤ qi ≤
qmax
± 1.4% for qmin ≤ qi ˂ qt
 Maximum peak-to-peak error :
………………………………….: 0.1% for qt ≤ qi ≤
qmax
1.4% for qmin ≤ qi ˂ qtts

35.  The usage for the smaller meters have been
slightly relaxed due to the difficulty it pose in
measuring acoustic transit times in turbulent
gas flow when the path lengths are shorter.

36.  The UM shall meet the above flow measurement
accuracy requirements over the full operating
pressure, temperature and gas composition
ranges without the need for manual adjustment;
unless other wise stated by the manufacturer.
 If the UM requires manual input to characterize
the flowing gas condition (e.g. gas density and
viscosity), the manufacturer shall state the
sensitivity of these dynamic parameters, so the
operator can see the need to change these
parameters relative to conditions change.