P. Saidi Reddy

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.

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.

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.

Multimode Fused Coupler Fiber Optic Pressure Sensor

The response of a pressure cell with copper diaphragm of different dimensions for the measurement of pressure using a fused multimode fiber optic coupler is presented. As the pressure varies, the deflection of the diaphragm varies and it modulates the intensity of the reflected light entering into the multimode fused coupler. The sensor is operated in back slope of its characteristic displacement curve and it enabled to sense larger range of pressures. The effect of variation of diameter and thickness of the diaphragm is also studied. The experimental results show that the sensitivity, linearity of the sensor is good and it may finds application in monitoring pressure in industries.

An encapsulated fiber optic fuel level sensor

An encapsulated fiber optic sensor head for the detection of level of fuel in a tank is presented. The design is based on a concentric cam used along with a float and extrinsic intensity modulation of light. The sensor has been tested for its performance to measure a fuel level range of 35cm and a sensitivity of 0.2316 volts/cm was observed during rise in fuel level. The sensitivity and range of level sensing can be varied by varying the length of the connecting rod.

Development of high sensitivity pressure sensorusing reduced clad FBG

This study focused on the development of high sensitivity pressure sensor based on reduced clad FBG encapsulated in a stainless steel cylinder, partially filled with silicon rubber. The sensor works by means of transferring radial or lateral pressure into an axially stretched- strain along the length of the FBG. The experiment is carried out using two different FBGs have core/clad diameters of 9/125μm (FBG1) and 4/80μm (FBG2). FBG2 is chemically etched to reduce the cladding diameter which significantly enhances the pressure sensitivity. The shift of the Bragg wavelength in response to applied pressure is monitored with an optical spectrum analyser (OSA). The measured pressure sensitivity of FBG2 and FBG1 are found to be 5.85 x 10-2 MPa-1 and 2.07 x 10-2 MPa-1, which are approximately 18870 and 6677 times respectively higher than that can be sensed with a bare FBG. A very good linearity is observed between Bragg wavelength shift and pressure. This compact, low cost and robust design of the sensor can find applications in the areas of low and medium pressure measurement.

Non-contact vibration sensor using bifurcated bundle glass fiber for real time monitoring

A fiber optic vibration sensor is demonstrated using bifurcated bundle fiber based on the principle of extrinsic displacement sensor. An IR source is used along with glass fibers to avoid the effect of stray light in sensing. The encapsulation of the sensor enables easy alignment, flexible handling and usage in harsh environments. The sensor is capable of measuring the frequencies up to 650Hz with vibration amplitude resolution of 10µm, enough to monitor the vibrations generated in heavy machines. The sensor is tested in the field to monitor the health condition of the diesel engine.