Simultaneous Measurement Of Liquid-level Research Articles

Simultaneous measurement of liquid level and refractive index based on a sandwich multimode optical fiber structure

Simultaneous measurement of liquid level and refractive index based on a sandwich multimode optical fiber structure

In-line reflected fiber sensor for simultaneous measurement of temperature and liquid level based on tapered few-mode fiber.

An in-line reflective dual-parameters fiber-optic sensor is proposed in this work, whereas it is experimentally verified by measuring both the liquid level and the local temperature distribution simultaneously. The proposed sensor configuration comprises a single-mode fiber (SMF), a tapered few-mode fiber (TFMF), as well as a silver-coated capillary tube. The extracted experimental results indicate that the liquid level only affects the power of the resonant dips, while having little impact on the wavelength. On the other hand, both the wavelength and the power of the resonant dips vary with the temperature change. Therefore, the simultaneous measurement of the liquid level and temperature can be realized according to the different responses of the resonant dips to the liquid level and temperature. The obtained liquid level and temperature sensitivities can reach the values of 0.106 dB/mm and 0.029 dB/°C, 35 pm/°C, respectively. The sensor exhibits the advantages of high stability and low cost, the demodulation relates on only one wavelength which can shorten the scanning wavelength range during measurement. The proposed sensor can be potentially applied where accurate and simultaneous measurements of both temperature and liquid level are required.

An inline Mach-Zehnder interferometer for simultaneously measuring liquid level and temperature

A compact optical fiber sensor (OFS) based on an inline Mach-Zehnder interferometer for simultaneousmeasurement of liquid level and the temperature isproposedanddemonstrated experimentally. The proposed sensor is formed by fusion splicing a thin core fiber (TCF) with an ultra-thin fiber (UTF) with core offset, then TCF and UTF are sandwiched between two standards of single mode fibers (SMFs). The liquid level or temperature change will lead to the dips shifts in the interference spectrum, and the liquid level and temperature sensitivities can be measured independently by monitoring the resonance dips shifts. Then the simultaneous measurement of liquid level and temperature can be obtained through the demodulation matrix. Four sensors with different UTF length are fabricated based on numerical simulation. The experimental results show that the proposed sensor with a UTF length of 8 mm has the optimal liquid level and temperature sensitivities of −231.67 pm/mm and 77.86 pm/°C, respectively. The measuring liquid level and temperature ranges are 0–8 mm and 30–60 °C. The proposed sensing configuration has practical application potential in various industries due to the advantages of high sensitivity, simple fabrication and low cost.

Simultaneous Measurement of Liquid Level and Temperature Using In-Fiber Grating-Based Mach-Zehnder Interferometer and Faraday Rotator Mirror.

Here we propose an optical fiber sensor capable of simultaneous measurement of liquid level and temperature by utilizing cascaded long-period fiber gratings (LPFGs) inscribed on high-birefringence fiber (HBF) and a Faraday rotator mirror (FRM). Due to the in-fiber Mach-Zehnder interference and birefringence of the HBF, these cascaded LPFGs have polarization-dependent discrete interference spectra, each of which is created within one of the two different attenuation bands obtained in the two orthogonal input polarization states, e.g., linear horizontal polarization (LHP) and linear vertical polarization (LVP). The minimum transmittance dip was selected as a sensor indicator for each interference spectrum obtained for LHP or LVP input signal. To monitor these indicator dips associated with LHP and LVP, referred to as the IDH and IDV, respectively, with one spectral scanning, an FRM was connected to the end of the cascaded LPFGs. Both the IDH and IDV spectrally shifted according to liquid-level or temperature changes and showed very linear responses to them with adjusted R₂ values greater than 0.997. The liquid-level sensitivities of the IDH and IDV were measured as approximately -37.29 and -121.08 pm/mm in a liquid-level range of 0 to 55 mm, respectively. The temperature sensitivities of the IDH and IDV were measured as ˜28.79 and ˜218.21 pm/°C in a temperature range of 30 to 60 °C, respectively. Owing to their linear and independent responses to liquid level and temperature, our sensor can perform temperature-independent liquid-level measurement using their pre-determined liquid-level and temperature sensitivities, even if both liquid level and temperature change simultaneously.

Multifunctional Admittance-Type Sensor and Its Instrumentation for Simultaneous Measurement of Liquid Level and Temperature

The admittance-type-level sensor is used for continuous level measurement in both metallic and nonmetallic tanks. However, the use of this sensor is limited because of the significant nonlinearity and cross-sensitivity. In this work, the authors have proposed the concept of a double-electrode admittance-type-level sensor. The said level sensor measures the level and the temperature of a conductive liquid. The multifunctional measurement is possible by the detection of the extent of cross-sensitivity using fuzzy logic and decomposition of the measurement variables. The experimental prototype of the sensor and associated instrumentation have been developed, and from the experimental results, it is found that the error in the measurement is consistently distributed and within the range of 1.86% for the level and 2.73% for temperature, which demonstrates the appropriateness of the design. This measurement system and sensor design can be implemented in the boiler-drum-level measurement for better drum-level control.

Liquid level measurement based on a no-core fiber with temperature compensation using a fiber Bragg grating

An optical fiber sensor for simultaneous measurement of liquid level and temperature is proposed and experimentally demonstrated. The sensor is formed by the integration of a no-core fiber (NCF) with a fiber Bragg grating (FBG).When the liquid level is changed, the interference fringe of the NCF would shift while the Bragg wavelength of the FBG remains the same. On the other hand, the interference fringe of the NCF and the Bragg wavelength of the FBG would shift simultaneously with the variation of temperature. Thus the liquid level sensor with dynamic temperature compensation can be easily achieved by using the temperature sensing property of FBG. For 10 pm wavelength resolution, the resolution of the sensor is 0.046cm and 1.1°C in liquid level and temperature, respectively. The fabrication of the proposed sensor is very simple and it is characterized by the dynamic temperature compensation, which makes it desirable in liquid level measurement.

Liquid level and temperature sensor based on an asymmetrical fiber Mach–Zehnder interferometer combined with a fiber Bragg grating

A fiber optic sensor capable of simultaneous measurement of liquid level and temperature is proposed and demonstrated. The sensor is formed by the integration of an asymmetrical fiber Mach–Zehnder interferometer (aFMZI) with a fiber Bragg grating (FBG). The aFMZI was realized by concatenating a fiber taper and a lateral-shifted junction. By using the temperature sensing property of FBG, the liquid level sensor with dynamic temperature compensation can be achieved. For 10pm wavelength resolution, a resolution of 0.15cm in liquid level and 1.01°C in temperature can be achieved. The prototype has the advantages of low fabrication cost and temperature compensated, which are desirable features in liquid level measurement.

Simultaneous Measurement of Liquid Level and Temperature Using Tilted Fiber Bragg Grating

We present a tilted fiber Bragg grating (TFBG)-based fiber optic sensor for the simultaneous measurement of liquid level and temperature. Due to different responses of cladding modes and core mode in TFBG spectrum to liquid level and temperature changes, both values can be measured independently. The examined 3.5° TFBG exhibits linear liquid level, as well as temperature, responses and sensitivities of −0.456 ± 0.009 dB/mm and 11.4 ± 0.2 pm/°C, respectively. In addition, greater sensor applicability is proposed for liquids having lower refractive indexes using TFBG with greater tilt angle. The presented system is capable of being applied in chemical, food, and automotive industries as well as, thanks to its all-fiber structure, in potentially hazardous environments where the immunity to electromagnetic fields or/and electric isolation is required.

Simultaneous measurement of liquid level and temperature based on spherical-shape structures and long period fiber grating

A Mach–Zehnder interferometer (MZI) for simultaneous measurement of liquid level and temperature is proposed. It is formed by embedding a long-period fiber grating in the middle of two spherical-shape fiber structures. Two Dips in the interference spectrum are selected to demonstrate the interferometer’s responses to the liquid level and temperature, and simultaneous measurement of liquid level and temperature can be realized by means of sensitivity coefficient matrix. The performances of two MZIs with different lengths are investigated. The results show that a high sensitivity of −0.214nm/mm for liquid level measurement is acquired for the 35mm sensor, and the temperature sensitivity is 0.059nm/°C in the range of 35–70°C.

A fiber laser sensor for liquid level and temperature based on two taper structures and fiber Bragg grating

A fiber laser sensor for simultaneous measurement of liquid level and temperature is proposed and demonstrated experimentally. The sensor is based on two taper structures and a fiber Bragg grating (FBG). The two taper structures form a novel fiber interferometer, which is fabricated by cascading two tapers in a section of single-mode fiber (SMF). The FBG and the interferometer serve as the filters of the laser cavity. Corresponding to the two filters, the laser outputs are stable dual-wavelength outputs, which have different characteristics to the liquid level and the temperature. The wavelength produced by the FBG is not sensitive to the liquid level. The temperature sensitivity of the wavelength produced by the FBG is 0.0123nm/°C. The wavelength produced by the interferometer is sensitive to the liquid level and the sensitivity is up to 0.2294nm/mm. The temperature sensitivity of the wavelength produced by the interferometer is 0.0648nm/°C. According to the different spectral responses of the liquid level and the temperature, simultaneous measurement can be realized. Furthermore, the proposed sensor has the advantages of less detection limit (DL), higher resolution and higher sensitivity compared to other optical fiber sensors.

Simultaneous measurement for liquid level and refractive index based on all-fiber modal interferometer

A simple fiber sensor capable of simultaneous measurement of liquid level and refractive index (RI) is proposed and experimentally demonstrated. The sensing head is an all-fiber modal interferometer manufactured by splicing an uncoated single-mode fiber with two short sections of multimode fiber. The interference pattern experiences blue shift along with an increase of axial strain and surrounding RI. Owing to the participation of multiple cladding modes with different sensitivities, the height and RI of the liquid could be simultaneously measured by monitoring two dips of the transmission spectrum. Experimental results show that the liquid level and RI sensitivities of the two dips are 245.7 pm/mm, −38 nm/RI unit (RIU), and 223.7 pm/mm, −62 nm/RIU, respectively. The approach has distinctive advantages of easy fabrication, low cost, and high sensitivity for liquid level detection with the capability of distinguishing the RI variation simultaneously.

Application of Fiber Bragg Grating Level Sensor and Fabry-Pérot Pressure Sensor to Simultaneous Measurement of Liquid Level and Specific Gravity

This study is proposed for obtaining simultaneous measurements of the level and specific gravity of a liquid using a dual-optical-fiber-sensor system comprising a fiber Bragg grating (FBG) level sensor and a Fabry-Perot (FP) pressure sensor. In the FBG level sensor, the liquid level is derived from the FBG wavelength shift induced when the buoyancy is applied on a cantilever beam. Meanwhile, in the FP sensor, the pressure is calculated from the change in cavity length which takes place when the sensor is immersed. The experimental results show that the FBG level and FP pressure sensors have sensitivities of 0.01491 nm/cm and 0.1569 μm/kPa, respectively. Analytical formulae are derived for the level and specific gravity of the liquid in terms of the Bragg wavelength shift, the change in cavity length, and the vertical separation distance between the two sensors. The average measurement errors of the liquid level and specific gravity are found to be 0.0323 and 0.0528 m, respectively.

Application of Fabry–Pérot and fiber Bragg grating pressure sensors to simultaneous measurement of liquid level and specific gravity

An approach is proposed for obtaining simultaneous measurements of the level and specific gravity of a liquid using a dual-pressure-sensor system comprising a fiber Bragg grating (FBG) pressure sensor and a Fabry–Pérot (FP) pressure sensor. In the FBG sensor, the pressure is derived from the FBG wavelength shift induced when the sensor is immersed in the liquid. Meanwhile, in the FP sensor, the pressure is calculated from the change in cavity length which takes place when the sensor is immersed. The advantageous concept of the dual-pressure-sensor system is atmospheric pressure compensation. The experimental results show that the FBG and FP pressure sensors have sensitivities of 0.1495nm/kPa and 0.1569μm/kPa, respectively. Analytical formulae are derived for the level and specific gravity of the liquid in terms of the FBG wavelength shift, the change in cavity length, and the vertical separation distance between the two sensors.

Simultaneous measurement of liquid level and surrounding refractive index using tilted fiber Bragg grating

In this paper, we present a novel fiber optic sensor for the simultaneous measurement of liquid level and surrounding refractive index based on tilted fiber Bragg grating (TFBG). The transmission loss and the bandwidth of cladding modes are two measures of the liquid level, while their resonance wavelengths are employed to determine the surrounding refractive index. A liquid level sensitivity of over 0.6 dB/mm is achieved with good linearity. Temperature independent surrounding refractive index sensing is possible using the Bragg mode of TFBG as a temperature reference. What is more, a scheme is proposed to realize a large measurement range of liquid level by connecting a certain number of TFBGs in series or parallel. The scheme is verified by an experiment in which three TFBGs are connected in parallel.

Tapered fibre Mach-Zehnder interferometer for simultaneous measurement of liquid level and temperature

A tapered fibre Mach-Zehnder interferometer sensor is presented to simultaneously measure liquid level and temperature. The transmission spectra shift with the change in immersed liquid level and environmental temperature. The liquid level difference of 190 mm can be measured with millimetre resolution in 90 mm-long linear range. The temperature response is discriminated from level response by simultaneously monitoring different interference orders at 1520 and 1620 nm. Level sensitivities of −0.017 and −0.021 nm/mm, and temperature sensitivities of 0.074 and 0.081 nm/°C are achieved, respectively.

Single uniform FBG for simultaneous measurement of liquid level and temperature

In this paper, we propose and demonstrate a novel scheme for simultaneous measurement of liquid level and temperature based on a simple uniform fiber Bragg grating (FBG) by monitoring both the short-wavelength-loss peaks and its Bragg resonance. The liquid level can be measured from the amplitude changes of the short-wavelength-loss peaks, while temperature can be measured from the wavelength shift of the Bragg resonance. Both theoretical simulation results and experimental results are presented. Such a scheme has some advantages including robustness, simplicity, flexibility in choosing sensitivity and simultaneous temperature measurement capability.