Craig Marshall takes a look at how smart flow meters will become smarter
Flow meter technology is now highly advanced, with the next key milestone being to make the equipment more cost -effective for the end user. This process will be enabled by the correct use of flow measurement diagnostics and secondary measurements to create smarter flow meters.
Advances in electronics has allowed the detailed monitoring of all the recorded data within a meter to be used as a diagnostic tool to complete a ‘health-check’ of the meter while it is in operation. By trending this information over time, changes can be linked to various flow disturbances to help resolve measurement accuracy issues. Some manufacturers have also created bespoke software for their meters, meaning that reports or live data can be accessed from anywhere in the world. Engineers can use this information to assess a meter’s ongoing performance, with alarms instantaneously alerting them to any problems.
Additionally, trending of the data over time can then be used to provide regulators and auditors with information on the present state of meters, with the aim of reducing the need for recalibration.
Recalibrations are both costly and labour intensive, particularly when multiple meters are involved. However, incorporating diagnostics and utilising smart meters could reduce this cost.
Taking a fingerprint of the diagnostic parameters during calibration can provide a traceable link to meter performance. Once the meter is installed for use in a process stream, comparing the fingerprint with calibration values can ensure no change or shift from the calibration. This provides confidence that the calibration is successfully transferred to the operating location and conditions.
Using qualitative information about the meter’s performance and embedded technical knowledge, the resultant flowrate information can be reassessed and a confidence level applied. If there is no shift in meter diagnostics i.e. fingerprint, over a period of time, this indicates that the meter has not shifted in service and therefore does not need a recalibration.
A good example of this is an ultrasonic meter with builtin diagnostic capabilities. An ultrasonic meter measures the time it takes for a pulse of ultrasound to traverse between two axially spaced transducers in both the forward and reverse directions. The ultrasound traverses through the flowing fluid medium where the signal is attenuated and distorted to some level. Measurement signal diagnostics such as signal strength, signal to noise ratio (SNR) and signal amplification (gain) can be monitored and trended over time to give an indication of meter performance. If these diagnostics do not change over the time period, there is an added confidence that the meter is still operating within specification and does not need to be recalibrated.
In addition to these signal diagnostics, a functional diagnostic parameter can be used in the form of the calculated speed of sound from each measurement path in an ultrasonic meter. The speed of sound can also be calculated using knowledge of the process conditions i.e. temperature, pressure and gas composition alongside industry standard calculations. By comparing the metercalculated speed of sound with one calculated from other process measurements it is possible to further verify not only the meter’s performance but also the performance of the other measurement instruments involved.
This technique can be used to validate a full measurement system, which can be extremely powerful and beneficial. For example, if the temperature measurement began to operate with a systematic bias, this would ripple through the speed of sound calculation method resulting in a discrepancy between the meter calculated value and the process measurement calculated value. This discrepancy would be highlighted by the alarm software and the user could take the appropriate action.
A smarter future
The use of diagnostics is not limited to the correction of measurement faults. For example, the use of diagnostics and secondary information will enable a condition-based monitoring recalibration timescale rather than a calendarbased one.
Potentially, the benefits do not stop at extending recalibration intervals and diagnostics could take industry a step closer to the realisation of a recalibration-free utopia. If shifts in diagnostics can be detected and attributed to a specific source then models could be used to predict and correct the measured result.
By having a good understanding of how diagnostics are generated in different metering technologies and how the different sources of shift in measurement performance influence their generation it may be possible to develop these relationships. Coupling this knowledge with new measurement techniques to identify and quantify the sources of shift would result in a very powerful tool for flow measurement technologies.
Technology is now advancing to a point where much more computer processing can be completed in real-time allowing for the opportunity to further develop the field of diagnostics and smart metering. In the near future, the use of diagnostics could eliminate the errors associated with issues that affect meter performance.
However, for true industrial scale uptake of smart meters, there will have to be evidence to support any models or systems developed in order to give end users confidence in their operation. At present, meters are much smarter than previous generations and are now able to qualitatively alert operators if something has gone wrong, but they are still unable to quantify the problem and correct themselves.
Anything that can reduce the input effort and cost for the end-user such as making meters recalibration free for the entirety of their operating lives will always be of interest. With the developments in technology and growing interest in diagnostics it can be said with confidence that smart meters are becoming smarter and are the future of flow measurement.
Craig Marshall is Project Engineer at NEL. NEL is a world-class provider of technical consultancy, research, measurement, testing and flow measurement services to the energy and oil & gas industries, as well as government.
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