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

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.

Simultaneous detection of liquid level and refractive index with a long-period fiber grating based sensor device

“…Liquid level detection was also reported with a 100 mm-long grating sensor in 2009 [18], a regular LPFG sensor in 2012 [19], and an LPFG modified Mach-Zehnder Interferometer in 2011 [20]. These advances of LPFG liquid level sensors further led to the development of reflective LPFG series for simultaneous fluid level and velocity detection [21].…”

Improved Fault Detection and Process Safety Using Multiscale Shewhart Charts.

“…The chart is applied on process residuals, without the utilization of any filters. It is computationally simple to implement [15]. Other univariate charts, such as EWMA (Exponentially Weighted Moving Average) and CUSUM (Cumulative Sum) charts utilize the application of linear filters, before carrying out fault detection and can be more computationally expensive [16][17][18].…”

An All Fiber Intrinsic Fabry-Perot Interferometer Based on an Air-Microcavity

“…Fiber optic interferometers have been investigated for a long period of time because of their potential application in several fields of science and technology [1–3], hence different interferometer fabrication techniques can be found in literature [4–7]. Among these of the most popular is the Fabry-Perot Interferometer (FPI) since it presents useful optical characteristics which allow us to measure different physical magnitudes such as pressure [5,8], strain [6], vibrations [6], temperature [9], refractive index (RI) [10,11] and magnetic field [12].…”