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.
Highlights
The primary motivation of this study is to develop and assess a light weight and low-cost long-period fiber grating (LPFG) sensor for the measurement of liquid level and fluid-flow velocity, which has the potential for use in civil engineering work such as health monitoring for pavement structures [1] and other applications such as liquid level monitoring of tanks or reservoirs for industrial sectors, debris flow monitoring and warnings for the tropical cyclone season, as well as water level and fluid-flow velocity monitoring for hydraulic applications such as pipes, channels, and dam facilities
The spectra of the mobile liquid level sensor with a 1,546.25-nm resonance wavelength LPFG is shown in Figure 4(a) and the sensor was immersed in air and in water when liquid level was equal to 10 cm
This paper presents the development and assessment of two types of LPFG-based sensors including a mobile liquid level sensor and a reflective sensor for the measurement of liquid level and fluid-flow velocity
Summary
The development and fabrication of LPFGs and the related measurands take place in many physical parameters, such as temperature, strain, refractive index (RI), bending, in-series, and multi-parameter sensing [2]. LPFGs are especially suitable for measurements and applications when liquids or solutions undergo a change in RI [2]. A liquid level sensor has been developed using LPFG technology; the measurand is the change in RI and the liquid is oil [4]. Liquid level sensors have been investigated using fiber Bragg grating (FBG) technology [5,6]. Other optical liquid level sensing systems include optical intensity, special D-shaped silica fiber, LED sensing, and fluorescent technologies [7–10]. The LPFG is extremely sensitive to the RI of the medium surrounding the cladding surface of the sensing grating region, allowing it to be used as an ambient index sensor [11–14]
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