Fiber optic pressure sensing has proven its reliability and accuracy in the harshest of environments. FBGS build pressure sensors with unique sensing capabilities eliminating the cross-sensitivity over wide temperature and pressure working ranges. The sensing system measures both with an outstanding stability under shock and vibrations conditions.
Fiber optic pressure sensing as turn-key
The fiber optic pressure sensor is a medium range hydrostatic pressure / temperature sensor, that monitors simultaneously between respectively 0 – 150°C and 0 – 700 bar. Its core consists of a Fiber Bragg Grating written inside an epoxy-free monolithic silica transducer, whereby transducer and waveguide element are contained in the same material. Its special patent-pending ruggedized housing is designed to withstand extreme conditions resisting both heat and vibrations. The inside of the housing contains a non-aggressive fluid and is in connection with the corrosive well fluid through a special pressure transfer mechanism that connects the outside well pressure to the internal fluid inside the housing.
During a pressure change, the wavelength of the reflected light is being affected due to the change of fiber birefringence. This pressure sensing mechanism has extremely low correlation with regards to the influence of temperature.
Furthermore, the solution allows multiplexed pressure measurement, e.g. along boreholes and pipelines for oil and gas exploration and transport.
Special topic cross-sensitivity
FBGS’ fiber optic pressure sensing features a unique extremely low cross-sensitivity between temperature and pressure. This property makes this sensor ideally suited for applications in environments where strong transient pressure or temperature are expected.
∙ Turn-key fiber optic pressure sensing system (fiber, measurement system, software)
∙ Decoupling between pressure and temperature: no cross-sensitivity
∙ Perfectly accurate pressure measurement in a temperature transient environment: no drift in calibration after a rapid temperature transient from 0 – 700 bar
∙ Easy integration in existing systems
∙ Solution tailored to customers’ needs
∙ Miniaturized size
∙ Resistant to shock and vibrations in oil & gas conditions and harsh environments
∙ Excellent pressure stability during temperature shocks at constant pressure
∙ Fast pressure response time of less than 1 second
Fields of application
Fiber optic pressure sensing is ideally suited for applications in challenging applications, where strong transient pressure or temperature environments are expected. The solution finds its way best in the fields of energy applications. The oil & gas industry uses the solution for its special very low cross-sensitivity between temperature and pressure. Together with the process industry they value its deployment in harsh environment where the data reading and processing can be made from afar in a control room.
Here are a few examples, where fiber optic pressure sensing can be integrated:
∙ Oil & gas: boreholes, sensing downhole environment, offshore downhole
∙ Temperature and pressure monitoring in gas chamber especially during pressurizing or depressurizing
∙ Pipeline and reactor monitoring
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Why is fiber optic pressure sensing particularly suited for oil & gas applications?
The oil & gas industry can be considered as one of the most challenging environments on Earth. While the temperature and pressure range easily raise up to several hundreds of degrees Celsius and bar and where rapid changes in temperature occur, fiber optic pressure sensing overcomes these difficulties with its unique sensing principle in order to provide accurate temperature and pressure measurement.
How / why can FBGS deliver a complete turn-key pressure sensing solution?
Relying on over a decade of experience in the fields of fiber optics, gratings and measurement devices, FBGS combine both technology and application know-how to achieve complete sensing solutions. The FBG-Scan unit, a spectrometer-based FBG device, features polarization insensitive measurement (low DOP broadband light source) and high scanning frequency (up to 2 KHz). This interrogator is a perfect match to MPT-01 pressure sensor as both the temperature and pressure are needed to be detected and calculated simultaneously. In the end, FBGS will be able to supply you from the pressure sensor and its suitable packaging all the way to its measurement device and the user-friendly read-out interface.
Moreover, we invest in research and development to keep improving our sensing system and tailor it to specific applications needs in the oil & gas industry.
How can I be sure, that the low pressure / temperature cross-sensitivity is real?
Thanks to the unique sensing principle of the sensor, temperature and pressure are being converted into different responses on its Bragg wavelength changes. A series of verification test on this topic has also been introduced in order to present its outstanding performance against cross-sensitivity. These results can also be seen in several publications.
Why is the housing so particular?
The pressure sensor consists of two main parts: the primary housing which hosts the fiber optic-based sensing element and the secondary housing which not only offers additional protection in harsh environments, but also allows pressure to be transmitted into the sensing element. The design of the secondary housing can be tailored to be compatible with varied applications.
The housing offers a robust mechanical protection and at the same time keeps away the corrosive materials from the sensing element in e.g. downhole environments. Although it offers enough protection, the sensing system does not delay the pressure response time.
How can FBGS pressure sensing solution achieve a response time of about one second?
The pressure transfer mechanism is based on sintered metal filter. This filter isolates corrosive material in the downhole but acts as a transparent material to pressure transfer. We have verified the pressure response times and the result have shown that the response is almost instantaneous within the scanning rate of the FBG interrogator.
Will the pressure sensing system survive shocks and vibrations and continue working properly?
FBGS pressure sensing solution has gone through an oil & gas rated vibration and shock test (NAVMAT9492) before deployment in an offshore downhole site. This prerequisite heavily validates the integrity of its sensing element and packaging with respect to the principal directions of the sensor. Results have shown that the sensor behaves functional with a limited pressure error during the tests. Moreover, an identical sensing performance is obtained which indicates pressure sensor is capable of measuring temperature and pressure during shock and vibration conditions.
How does fiber optic pressure sensing work?
Fiber optic pressure sensing is based on one single grating written in a highly birefringent fiber. Due to its high birefringence, two Bragg peaks corresponding to the slow and fast axis of the fiber can be seen. The pressure sensing principle relies on asymmetrically concentrating the hydrostatic pressure into its optical core where the grating is written. This will lead to the change of fiber birefringence and can be seen on the differential wavelength shift. As the monitoring of both temperature and pressure are done through different mechanisms, the cross-sensitivity between these two parameters is extremely low.