Traditional Electrical Sensors Research Articles

Suppression of Instability on Sensing Signal of Optical Pulse Correlation Measurement in Remote Fiber Sensing

Optical fiber sensing has the potential to overcome weak points of traditional electric sensors. Many types of optical fiber sensors have been proposed according to the modulation parameter of incident light. We have proposed an optical pulse correlation sensing system that focuses on the time drift values of the propagating optical pulses to monitor the temperature- or strain-induced extension along the optical fiber in the sensing region. In this study, we consider the instability in the optical pulse correlation sensing system applied to remote monitoring over a kilometer-long distance. We introduce a method to stabilize the instability of the pulse correlation signal resulting from the time drift fluctuation along a transmission line. By using this method, we can purify the response and improve the accuracy of signals at the focused sensing regions. We also experimentally demonstrate remote temperature monitoring over a 30 km-long distance using a remote reference technique, and we estimate the resolution and the measurable span of the temperature variation as(1.1/L)∘Cand(5.9×10/L)°C, respectively, whereLis the length of the fiber in the sensing region.

Voltage Controlled White Light Polarization Interference Demodulation in Fabry-Perot Cavity Fibre Sensor System

Fibre optical sensors (FOS) have been paid a lot of attention because of innate immunity of electro-magnetic interference (EMI) and high precision, especially like Fabry-Perot (F-P) cavity fibre sensor which is tiny and sensitive. However, FOS hasn’t taken place of traditional electric sensors for its complex and expansive demodulation of optical signal. A new demodulation method using white light polarization interference controlled by voltage is proposed in this paper. In the system, a birefringence crystal plays a pivotal role in making optical path difference (OPD) between ordinary linear light and extraordinary linear light. When the OPD compensated with the length of F-P cavity, the output signal produces fringe patent. The OPD between the two orthogonal linear polarized lights is also controlled by an electronic field acted on the birefringence crystal. According to the Pockels effect, the change of ODP is linearly depended on intensity of electronic field. The length of cavity can be calculated by a voltage scanning. The mathematic model of voltage controlled demodulation is derived and the simulation result is discussed. At last, fabrication processes are described and the key parameters are given.

Fabry‐Pérot Fiber‐Optic Sensors for Physical Parameters Measurement in Challenging Conditions

Optical fiber sensors have unique advantages and distinctive features that make them very attractive for many applications especially those involving challenging conditions where other traditional electrical sensors usually fail. Among the commercially available optical fiber sensors, the Fabry‐Pérot sensing technology is probably the most versatile and the most interesting one since a relatively low‐cost universal signal conditioner could easily read compatible Fabry Pérot sensors measuring different physical parameters such as strain, temperature, pressure, displacement, or refractive index. This papers details the numerous advantages of this optical sensing technology and also summarizes the operating modes of commercially available signal conditioners and sensors.

In-fiber Bragg-grating temperature sensor system for medical applications

A novel quasidistributed in-fiber Bragg grating (FBG) temperature sensor system has been developed for temperature proving in vivo in the human body for medical applications, e.g., hyperthermia treatment. This paper provides the operating principle of FBG temperature sensors and then the design of the sensor head. High-resolution detection of the wavelength-shifts induced by temperature changes are achieved using drift-compensated interferometric detection while the return signals from the FBG sensor array are demultiplexed with a simple monochromator which offers crosstalk-free wavelength-division-multiplexing (WDM). A strain-free probe is designed by enclosing the FBG sensor array in a protection sleeve. A four FBG sensor system is demonstrated and the experimental results are in good agreement with those obtained by traditional electrical thermocouple sensors. A resolution of 0.1/spl deg/C and an accuracy of /spl plusmn/0.2/spl deg/C over a temperature range of 30-60/spl deg/C have been achieved, which meet established medical requirements.