Fixed-length Logging Cable Device Based On Laser Doppler Effect

In the oil and gas field development process, the well depth measured by measuring the length of running cable, but the current cable length measurement mainly by motor and Martin Dyke wellhead two measurement methods. They are contact measurement, which must produce a large error caused by the contact measurement, so may affect the exact position of some important parameters in the oil and gas field development. In this paper, to avoid the current-contact measurement of the drawbacks, a laser Doppler Effect based on the non-contact cable length measurement is used. From the two-beam laser transmitter coherent incident laser light go through the convergent lens and assemble on the cable surface, and produce scattering, photoelectric detector receives two beams of light scattering which are in different directions for beat frequency, to obtain a laser Doppler frequency shift which is proportional to the cable speed. To analyze the signal, we can obtain the cable speed, and then integrate the speed on time to obtain the length of running cable.This paper describes the design principles of a laser Doppler device Measuring, using optical heterodyne detection to detect the laser Doppler frequency shift signal, the optical arrangement using a dual beam mode-to the receive mode after the double scattering. In this paper has completed the whole design of the optical system, provided the important calculation of the optical parameters.According to the characteristics of laser Doppler signal, using the fast Fourier transform to deal with the Doppler signal. The entire unit includes the next-bit PC data acquisition and monitoring two parts. CPU is TMS320VC5402 of the DSP series, the next bit mechanical and electrical units include:integrated operational amplifier based on the current-voltage converter circuit, second-order Butterworth low pass filter circuit, analog to digital conversion based on ADS803 circuit, external expansion memory circuit and communication with the host computer interface circuit.The lower computer software designs by CCS-based integrated development environment, this paper described a systematic process to achieve load bootstrap method, described FIR digital filter and data processing used FFT transform in DSP implementation. Using LabVIEW programming language to implement the design of the PC procedures, the PC program include:serial port communication parameters of the configuration procedures, data processing and display program, data storage and the program of historical data calling.