Optic Fiber Displacement Measurement Technology Based On The Phase Difference Demodulation

The optical fiber sensor system is insensitive to the electromagnetic interference and easy to be utilized,which makes it widely used in engineer field.Nowadays,optical fiber displacement sensor system monitors the outside physical quantities through demodulation Bragg grating wavelength drift or brillouin scattering light frequency drift.Although the measuring accuracy is more higher,but the demodulation system is complex and high cost.In order to solve the above problems,this paper designs optic fiber displacement measurement system of low cost,long distance measurement and simple demodulation.It is expected to help further application on optical fiber sensor monitor of long distances.This paper introduces the optical fiber system of Bragg grating and the measure displacement of using brillouin scattering.On the other hand,we know the problem of the adjustment system.On this basis,this paper puts forward a method of using the phase difference to demodulation the signal,and then get the change of the displacement of the body,it solves the problem that temperature and strain on the demodulation results.It is mainly suitable for long-range displacement monitor in large engineers.In the section of the sensor network system,we study the principle of phase-locked amplifier and design the corresponding hardware circuit.Several phase difference demodulation techniques are analyzed,including phase difference demodulation based on the analog phase-locked,the phase difference demodulation based on the digital xor gate circuit and the phase difference demodulation based on the digital signal The advantage and disadvantage of these technologies are compared.On that basis,we propose the phase difference demodulation based optical fiber sensor system to measure displacement,where the pulse trains work as the modulation signal.Then we design the photoelectric detection circuit and generate the two local reference signals.Finally,the corresponding algorithm and the drive control procedures are introduced.In order to characteristic the performance of our system,six different optical fibers are utilized in our experiment.For each measurement,two of the six fibers are selected and connected to the test system.After 15 times measurement,the demodulate values of length difference are compared with the actual length differences of the tested fibers,which turns out that the measurement accuracy of our system is 0.32229 cm.At the same time,a good linearity appears between the demodulated values and the actual values.This paper designs a set of optical fiber displacement measurement system based on phase difference demodulation scheme.The feasibility of this system is verified experimentally.This low cost sensor system comprises of highly reused optical fibersand the simple demodulation circuit,which is extremely suitable for the application in the large engineers.