R. L. N. Sai Prasad

Temperature compensated liquid level sensor using FBGs and a bourdon tube

A temperature compensated liquid level sensor using FBGs and a bourdon tube that works on hydrostatic pressure is presented. An FBG (FBG1) is fixed between free end and a fixed end of the bourdon tube. When hydrostatic pressure applied to the bourdon tube FBG1 experience an axial strain due to the movement of free end. Experimental result shows, a good linearity in shift in Bragg wavelength with the applied pressure. The performance of this arrangement is tested for 21metre water column pressure. Another FBG (FBG2) is included for temperature compensation. The design of the sensor head is simple and easy mountable external to any tank for liquid level measurements.

An FBG based hydrostatic pressure sensor for liquid level measurements

A small and simple hydrostatic pressure sensor using fiber Bragg grating sensor for liquid level sensing is reported. The working principle of the sensor head design is based on transferring hydrostatic radial pressure to axial strain to the FBG. An FBG written in a fiber of diameter 50μm has been used for the measurement. The experimental result shows that sensitivity of the sensor can reach 23pm/cm of liquid column. The sensor can be useful in applications that involved with less hydrostatic pressure, like a tank with inflammable liquid in a fuel gas station.

FBG-based novel sensor for high-temperature measurement and its low-cost interrogation

A novel sensor for high-temperature measurement using Fiber Bragg grating (FBG) along with its low-cost interrogation system has been designed and tested. The sensor works based on measurement of the shift in Bragg wavelength that corresponds to the temperature induced strain by making use of a mechanical transducer. The transducing element provides temperature dependent strain on FBG by means of differential linear thermal expansion of two different materials, stainless steel and mild steel. The shift in Bragg wavelength of FBG due to this temperature induced strain is measured by using optical spectrum analyser (OSA). Further the bulk and expensive OSA is replaced by a low cost interrogation system that employed an LPG, a photodiode, a transimpedance amplifier, and a digital multimeter. The LPG converts wavelength information of FBG into its equivalent intensity modulated signal which is captured by a simple photodiode and then converted into voltage signal using the transimpedance amplifier. The designed sensor measures the temperature from 20°C to 1000°C with a resolution of 2°C.

FBG-based temperature sensor package

A fiber Brag grating (FBG)-based temperature sensor accompanying with low cost interrogation scheme and LCD display has been designed and tested. The designed sensor measures the temperature from 20°C to 500°C with 1°C resolution.

A simple underground liquid level sensor using FBG

In this paper a packaged sensor using fiber Bragg grating for under water level measurement is presented. The sensor is configured by fixing one end of a fiber Bragg grating with a diaphragm made up of polymer kept inside a hollow cylinder and the other end to the cylinder. As the level of water increases in the tank hydrostatic pressure at the bottom also increases. The diaphragm used in is to transfer this pressure to the axial strain on the grating. By utilizing the unique diaphragm‐based grating packaging method, the level sensing range has been effectively enhanced. The results obtained indicate that this packaged sensor have long range, rugged and can be customized depending on the requirement. The sensitivity of the sensor is 6.057×10−6 per cm within the range 0 to 30 cm.

Simultaneous measurement of temperature and pressure sensor for oceanography using Bragg gratings

Pressure and temperature are fundamental properties of the oceanic water. They have varying effects on the processes that take place in oceans be they biological, physical or chemical while pressure always increases with respect to surface when you go down, temperature has a more complex variation with respect to the depth. Various tools and techniques are available to measure these properties. A combination sensor with high accuracy and response time would enable better measurements of these two parameters. This paper presents a novel structure based on simultaneous measurement of temperature and pressure sensing using Fiber Bragg grating (FBG) sensors. For this, proposed sensor heads for both temperature and pressure. Temperature measurement, two different types of sensor heads has been designed for this implementation. The first sensor head consists of a FBG which is fixed between ceramic block on one side and a bimetallic strip made up of aluminum and copper on the other. The second sensor head consists of the FBG which is fixed between two bimetallic strips. For pressure, in first type the FBG is fixed between silicon rubber foil and sensor head wall. In second method the FBG is fixed between two silicone rubber foils. The pressure on walls of silicon rubber foils elongates FBG, which results in shift of wavelength. Theoretical studies carried out on these proposed sensor heads resulted in an increase in temperature sensitivity of about six times greater than that of bare FBG sensor and pressure sensitivity of about eight times greater than that of bare FBG. Further, the proposed sensors have shown good linearity and stability.

Fiber optic liquid level sensor using multimode fused coupler

An intensity based fiber optic liquid level sensor for continuous measurement is described. The sensing principle is based on intensity of reflected light which is disturbed by the change in proximity of the fiber probe and the reflector. A Mechanical CAM is used in the sensing arrangement. It converts the rotatory motion into a linear displacement. As the liquid level raises, rotation of the CAM takes place and the CAM follower connected to it moves linearly. A reflector which is attached to the end of the CAM follower reflect the incident light. As the displacement of reflector occur the intensity of reflected light also changes and is a measure of change in liquid level. The prototype designed sensor can sense liquid level upto 17cm. The proposed sensor can find potential applications in transportation and process industries.An intensity based fiber optic liquid level sensor for continuous measurement is described. The sensing principle is based on intensity of reflected light which is disturbed by the change in proximity of the fiber probe and the reflector. A Mechanical CAM is used in the sensing arrangement. It converts the rotatory motion into a linear displacement. As the liquid level raises, rotation of the CAM takes place and the CAM follower connected to it moves linearly. A reflector which is attached to the end of the CAM follower reflect the incident light. As the displacement of reflector occur the intensity of reflected light also changes and is a measure of change in liquid level. The prototype designed sensor can sense liquid level upto 17cm. The proposed sensor can find potential applications in transportation and process industries.

Enhancing the temperature sensitivity of fiber Bragg grating sensor using bimetallic strip

This paper presents theoretical and experimental results carried out on a simple structure based on bimetallic cantilever to enhance temperature sensitivity of fiber Bragg grating (FBG) sensors. Two metals of equal length and width but having different coefficients of thermal expansion (CTE) are bonded with electric arc welding to form the bimetallic strip and FBG was longitudinally affixed to that metallic strip having larger coefficient of thermal expansion. It was observed that the temperature sensitivity of the proposed FBG sensor has increased 5 times more compared to the bare FBG sensor. Moreover, the proposed sensor showed excellent linearity, reversibility, and repeatability.

An improved low temperature sensing using PMMA coated FBG

Fiber Bragg Gratings have been shown to have a much improved thermal sensitivity when coated by Polymethyle methacrylate (PMMA) at cryogenic regime has been proposed. The PMMA has large thermal expansion coefficients and acts as driving elements. It is coated on the FBG at room temperature and the FBG is under compression at lower temperatures. This allows a much wider tuning of Bragg grating as fiber can stand at more compression than tension. An overall sensitivity of 0.039nm/K in the 1550nm wavelength regime has been achieved and the Bragg wavelength has been tuned upto 8.97nm in the temperature range 77K to 303K.

An FBG sensor for strain and temperature discrimination at cryogenic regime

A simple technique to discriminate the Strain and Temperature with a single Fiber Bragg Grating (FBG) at cryogenic regime is presented in this paper. An uniform FBG is divided into two parts, one half is without coating (FBG1) and other half is coated with Cyno-Acrylic Adhesive (FBG2). The measured temperature and strain sensitivities of the FBG1 are 4.05×10⁻⁶/K and 2.13×10⁻⁶/µε and FBG2 are 1.39×10⁻⁵/K and 1.72×10⁻⁶/µε respectively.