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Sensors 2012, 12(4), 4578-4593; doi:10.3390/s120404578
Article

Long-Period Fiber Grating Sensors for the Measurement of Liquid Level and Fluid-Flow Velocity

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Received: 30 December 2011; in revised form: 2 April 2012 / Accepted: 3 April 2012 / Published: 10 April 2012
(This article belongs to the Section Physical Sensors)
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Abstract: This paper presents the development and assessment of two types of Long Period Fiber Grating (LPFG)-based sensors including a mobile liquid level sensor and a reflective sensor for the measurement of liquid level and fluid-flow velocity. Shewhart control charts were used to assess the liquid level sensing capacity and reliability of the mobile CO2-laser engraved LPFG sensor. There were ten groups of different liquid level experiment and each group underwent ten repeated wavelength shift measurements. The results showed that all measurands were within the control limits; thus, this mobile sensor was reliable and exhibited at least 100-cm liquid level measurement capacity. In addition, a reflective sensor consisting of five LPFGs in series with a reflective end has been developed to evaluate the liquid level and fluid-flow velocity. These five LPFGs were fabricated by the electrical arc discharge method and the reflective end was coated with silver by Tollen’s test. After each liquid level experiment was performed five times, the average values of the resonance wavelength shifts for LPFG Nos. 1–5 were in the range of 1.35–9.14 nm. The experimental findings showed that the reflective sensor could be used to automatically monitor five fixed liquid levels. This reflective sensor also exhibited at least 100-cm liquid level measurement capacity. The mechanism of the fluid-flow velocity sensor was based on analyzing the relationship among the optical power, time, and the LPFG’s length. There were two types of fluid-flow velocity measurements: inflow and drainage processes. The differences between the LPFG-based fluid-flow velocities and the measured average fluid-flow velocities were found in the range of 8.7–12.6%. For the first time to our knowledge, we have demonstrated the feasibility of liquid level and fluid-flow velocity sensing with a reflective LPFG-based sensor without modifying LPFGs or coating chemical compounds.
Keywords: long-period fiber grating (LPFG); sensor; Shewhart control chart; refractive index (RI); wavelength shift; liquid level; fluid-flow velocity long-period fiber grating (LPFG); sensor; Shewhart control chart; refractive index (RI); wavelength shift; liquid level; fluid-flow velocity
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Wang, J.-N.; Luo, C.-Y. Long-Period Fiber Grating Sensors for the Measurement of Liquid Level and Fluid-Flow Velocity. Sensors 2012, 12, 4578-4593.

AMA Style

Wang J-N, Luo C-Y. Long-Period Fiber Grating Sensors for the Measurement of Liquid Level and Fluid-Flow Velocity. Sensors. 2012; 12(4):4578-4593.

Chicago/Turabian Style

Wang, Jian-Neng; Luo, Ching-Ying. 2012. "Long-Period Fiber Grating Sensors for the Measurement of Liquid Level and Fluid-Flow Velocity." Sensors 12, no. 4: 4578-4593.


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