Multi-Path
Ultrasonic Meter
Diagnostics
For Field Verification
Improvement
in the wet flow calibration helps in reducing the uncertainty of the
meters, while with the improved diagnostic software, the operators will
have better tools to perform troubleshooting, highlight Dan Hackett
and Kevin Chin.
Introduction
Most
customers have now started to use ultrasonic meters for natural gas
custody transfer metering. As a stand-alone meter, it can give diagnostics
information on the performance of the meter, but not enough to determine
a benchmark on its performance to a certain reference. This is where
external diagnostic would be required to enhance customer’s confidence
in the overall metering system performance. This article will focus
on these various techniques, and how they are being used.
Before
moving ahead with the field verification using SOS on flow computer,
it is important to highlight some of the recent developments in improving
the performance and diagnostics of ultrasonic metering system. They
include:
-
Enhanced/Improved Wet Flow Calibrations
-
Improved Diagnostic Software
-
Incorporate Speed of Sound (SOS) calculation in flow computers for
online verification, and
-
Remote Diagnostic
An
example and update on the latest development in AGA-9 [1] Working Group
would follow.
Enhanced/Improved
Wet Flow Calibrations
The
initial wet flow calibrations are based on 6-points or 8-points and
corrected on a single Flow-Weighted-Mean-Error (FWME) curve. With the
need to improve the accuracy and reduce the uncertainty, flow laboratories
have implemented various corrections, such as polynomial correction
curve fit, and recently, the multi-point linearisation method, is being
adopted. Figure 1 shows the single FWME curve.
This
enhanced and improved wet flow calibration reduces the uncertainty of
the meters, as it tries to adjust the measured value to its true value.
Figure 2 shows the polynomial correction curve before and after adjustment.
Another
method in correcting the meter to the zero-error baseline is the Multi-Point
Linearisation. This method is not new, as it is being done on turbine
meter calibration. Figure 3 shows how the points will be adjusted after
linearisation.
A
meter factor will be assigned at each calibrated point, and hence, the
‘As Left’ should be a straight line.
Improved
Diagnostic Software
Diagnostic
software has also improved over the last few years. The use of this
software is to determine the status of the meter’s performance, as well
as for troubleshooting purposes. The information obtainable from this
software is mainly:
-
Gains
-
Signal Quality
-
Signal to Noise Ratio
-
Speed of Sound
-
Velocity Profile
-
Individual Chord Waveform
The
latest CUI (Customer Ultrasonic Interface) software not only gives the
above information, but also provides numerous features allowing easier
operation and configuration of ultrasonic meter parameters.
These
new features are:
- Configuration
of new USM through wizard setup. Figure 4 shows the Wizard setup screen.
- Single
page Witness and Inspection Report. This report indicates the meter’s
main configuration, as well as a snap shot of the performance, and
can be signed off by customer. Figure 5 shows the report.
- Single
Screen on monitoring the meter’s performance. Figure 6 shows the Meter
Monitor screen.
- USM
configuration verification. This compares the meter’s configuration
to a master configuration in PC/laptop hard drive.Figure 7 shows an
example.
- Merging
Log Files.
- Speed
of Sound (SOS) calculation, and
- Remote
diagnostics
In
order to access the information from the ultrasonic meter, a Personal
Computer (PC) or laptop will be required. All access to the meter should
preferably be direct from PC or laptop, and not through the flow computer.
Since the meter would be installed in the field, and the flow computer
and PC/laptop would be operated in the control room, the ultrasonic
meter shall have two serial ports, preferably both RS-485 serial link.
....contd
