Flow meter monitoring advance
13 Sep 2006
Emerson’s market feedback surveys have showed enhanced condition monitoring capabilities very close to the top of the list of customer requirements, Chuck Stack, director of technology at Micro Motion, at a recent presentation in London.
The “self-verification technology” reduces meter validation efforts and costs — including the need to stop the process — and enables predictive maintenance that addresses issues such as erosion, cracking, pitting or coating within the meter, said Stack.
“One of the biggest expenses for companies working with Coriolis meters is taking the meter out for verification, continued Stack. He cited examples of a pharma industry customer spending $500,000 a year on this activity and an oil & gas client who reckoned that taking out meters cost up to $3,000/year per device.
Micro Motion’s solution involves comparing mechanical and electrical properties of the Coriolis meter against a baseline established at the factory prior to shipment. For example, Stack showed how by monitoring changes in tube stiffness the system could detect erosion in flowmeters used in an oil & gas application.
The method, which takes a few minutes to run, is enabled by next generation multivariable digital (MVD) technology, said Stack. The resulting real-time data shows operators if the performance of the Coriolis meter is changing and alerts them to non-conformance issues, he said.
Micro Motion pioneered MVD technology for Coriolis some years ago to advance meter performance by moving from a 9-wire based analogue signal processing meter to a completely digital 4-wire meter. Next-generation MVD, it claims, enables Coriolis meters to deliver even more information about the health of the meter and the performance of a process.
With the new technology. the customer initiates the meter verification through the transmitter, which vibrates a sensor to test tones that excite the sensor at multiple frequencies, a Micro Motion spokesman explained. The transmitter, he said, uses the sensor response to determine if the sensor characteristics have changed and measures the stiffness of the Micro Motion ELITE sensor. The system then signals if the mass flow measurement exceeds the limits specified by the customer.
“The transmitter sends sinusoidal signals, at multiple frequencies called input tones, to the sensor, either through a Micro Motion transmitter or using the Emerson AMS or ProLink software. The sensor behaves as a simple spring mass system and the sinusoids output by the transmitter act as frequency dependent forces," continued the spokesman. "These forces excite the spring/mass system and the amplitude of excitation is dependent on the frequency of excitation, sensor stiffness and sensor mass.”
At low frequencies, the excitation force acts as a static load rather than a dynamic load so inertial/mass effects are not present. The amplitude is, therefore, only related to the stiffness of the sensor, according to the spokesman.
"Conversely at high frequencies inertial effects dominate as a spring does not have time to respond and the amplitude is dependant only on the mass. Thus by vibrating the sensor at multiple frequencies, the sensor stiffness can be measured directly and be used to indicate tube damage,” he stated.
Emerson officials conceded that it would take time to establish the technology, not least because of tight regulation of the production regimes in many of the target applications. As Stack explained: “Customers have to be able to introduce changes to working practices, otherwise they don’t get the value of it.”
The Micro Motion engineer predicted that the self-verification technology is likely to be introduced first on a trial basis among major pharmaceutical majors, before finding more widespread commercial adoption.
According to Micro Motion's spokesman, the easiest way of getting general acceptance may be for key pharmaceutical and biotech companies to run their existing meter calibration or verification methods in parallel with the Micro Motion structural Integrity method of meter verification. This, he said, "will allow them to build on their own history and gradually change their methods overtime, with the blessing of the FDA.”
