Jiangdong Deng

Optical fiber sensor-based detection of partial discharges in power transformers

Abstract In this paper, a fiber optic acoustic sensor system is designed and tested for on-line detection of the partial discharges inside high voltage power transformers. The fiber optic sensor uses a silica diaphragm and a single mode optical fiber encapsulated in a silica glass tube to form an extrinsic Fabry–Perot interferometer. Test results indicate that the developed fiber optic sensors are capable of detecting the acoustic signals propagating inside the transformer oil with high resolution and high frequency.

Single-crystal sapphire fiber-based strain sensor for high-temperature applications

Single-crystal sapphire fibers have a very high melting point (up to 2050/spl deg/C), which renders them a very good candidate for sensing applications at a very high temperature. We present in this paper the recent work of developing single-crystal sapphire fiber extrinsic Fabry-Perot interferometric strain sensors based on the white-light interferometric spectrum demodulation technique. Prototype sapphire strain sensors were fabricated and tested at high temperatures up to 1004/spl deg/C. The preliminary experimental results indicate that the sensors are promising to be used under high-temperature environments for making strain measurements with strain measurement resolution of 0.2-/spl mu/ strain.

Fiber optic pressure sensor with self-compensation capability for harsh environment applications

A novel fiber optic pressure sensor system with self-compensation capability for harsh environment applications is reported. The system compensates for the fluctuation of source power and the variation of fiber losses by self-referencing the two channel outputs of a fiber optic extrinsic Fabry-Perot interfrometric (EFPI) sensor probe. A novel sensor fabrication system based on the controlled thermal bonding method is also described. For the first time, high-performance fiber optic EFPI sensor probes can be fabricated in a controlled fashion with excellent mechanical strength and temperature stability to survive and operate in the high-pressure and high-temperature coexisting harsh environment. Using a single-mode fiber sensor probe and the prototype signal-processing unit, we demonstrate pressure measurement up to 8400 psi and achieved resolution of 0.005% (2σ=0.4 psi) at atmospheric pressure, repeatability of ±0.15% (±13 psi), and 25-h stability of 0.09% (7 psi). The system also shows excellent remote operation capability when tested by separating the sensor probe from its signal-processing unit at a distance of 6.4 km.

Fiber optic pressure and temperature sensors for oil down hole application

Detailed studies on fiber optic pressure and temperature sensors for oil down-hole applications are described in this paper. The sensor head is an interferometric based fiber optic senor in which the air-gap will change with the pressure or temperature. For high-speed applications, a novel self-calibrating interferometric/intensity-based (SCIIB) scheme, which realizes compensations for both the light source drift and the fiber loss variation, was used to demodulate the pressure (or temperature) signals. An improved white light system was developed for sensor fabrication. This system is also used as the signal demodulation system providing very high resolution. Experiment results show that the SCIIB system achieves 0.1% accuracy with a 0-8000psi working range for the pressure sensor and a 0-600 degree(s)C working range for the temperature sensor. The resolution of the white light system is about +/- 0.5 nm with a dynamic range up to 10 micrometers. The long -term testing results in the oil site are also presented in this paper.

SCIIB pressure sensors for oil extraction applications

Efficient and complete recovery of petroleum reserves from existing oil wells has proven difficult due to a lack of robust information that can monitor processes in the downhole environment. Commercially available sensors for measurement of pressure, temperature, and fluid flow exhibit lifetimes in the harsh downhole conditions, which are characterized by high pressure (up to 20 kpsi), temperatures up to 250 degree(s)C, and exposure to chemically reactive fluids. Development of robust sensors that deliver continuous, real- time data on reservoir performance and petroleum flow pathways will facilitate application of advanced recovery technologies, including horizontal and multi-lateral wells. We describe the development and fabrication of pressure, temperature, and flow sensors designed for the downhole environment, based on the Self-Calibrated Interferometric/Intensity-Based configuration, which combines the high sensitivity of interferometric sensors with the high-speed of intensity-based sensors. By splitting the output of a Fabry-Perot sensor into two channels with differing coherence, unwanted perturbations, such as source power fluctuations and variations in fiber loss, may be compensated. Results of laboratory tests of prototype sensors demonstrate excellent resolution and accuracy.

Absolute Sapphire Optical Fiber Interferometric Sensors

Sapphire optical fiber sensor are greatly promising for high temperature sensing applications because of their high melting point, which exceeds 2000 degrees C. The extrinsic Fabry-Perot interferometric (EFPI) sapphire fiber sensors, based on absolute white light spectrum scanning signal processing, are extremely attractive in engineering applications because they do not require initialization and/or calibration when the system is turned on. Furthermore, it is not necessary to operate them in linear regions to avoid nonlinear effects, a significant problem in other EFPI sensor. In this paper, we use a single-crystal sapphire fiber for making an EFPI sensor. Interference fringes were observed by using both laser and light emitting diode sources. The effect of the lead-in fiber diameter on fringe visibility is also discussed.

Self-calibrated interferometric/intensity-based (SCIIB) optical fiber pressure sensor

A novel self-calibrated interferometer/industry-based (SCIIB) fiber optic sensor is described in this paper. The novel sensing scheme combines the advantages of both fiber interferometry senors and intensity-based sensors. The sensor operates on a single fiber Fabry-Perot interferometric cavity with a white light source. The interference signal of the sensor is coherent-sliced into two channels. Which allow fully real-time compensation for the source power drifting and fiber los variation. Temperature and pressure sensors with various dynamic ranges were designed and fabricated based on the SCIIB technology. Experimental result show that the SCIIB sensor scheme achieves excellent resolution and accuracy with the self- calibration function.

Fiber optic white light interferometric spectrum signal processing for absolute measurements

We present that development of a whitelight interferometric spectrum based signal processing method for fiber optic absolute sensing. The signal processing method achieves an extremely high resolution over a large dynamic range. The signal processing techniques are demonstrated on a whitelight fiber optic sensor system which uses a broadband LED as its source, and an low finesse extrinsic Fabry-Perot cavity as its sensing element. The interferometric spectrum from the sensor is received and processed through a computer compatible spectrometer which used a grating to disperse the light and a CCD array to record the spectrum. The experimental results show that the system achieves absolute measurement with nanometer accuracy over a range of more than 16 micrometers .

Thin-silica-diaphragm-based fiber optic acoustic sensors

In this sensor, we demonstrate the developing and testing of fiber optic sensors intended to detect acoustic waves. The sensor is based on a novel design housing a thin silica diaphragm and a single mode fiber in an extrinsic Fabry- Perot interferometric structure. The designed sensor is tested for different applications including the detection of the partial discharges inside a power transformer. The test results indicate that the designed sensor can detect acoustic signals with high sensitivity at frequency as high as 200 kHz.

High-pressure fiber optic acoustic sensor

This paper describes a diaphragm-based external Fabry-Perot interferometric (EFPI) fiber acoustic sensor with pressure-isolation structure. The structure minimizes the crosstalk generated by environmental pressure while enables considerable amount of acoustic signal power being delivered to the sensor, which allows the sensor to work in high-pressure environment. The detailed analysis on sensor design, pressure isolation and sensor fabrication as well as sensor performance are presented.