Research On Real-time Data Compression In Magnetic Flux Leakage Detecting System

With the development of on-line pipeline technology, people pay more attention to the security of oil-gas pipeline. Pipeline MFL detecting instrument is a typical device in the field of pipeline detecting. However, the volume of MFL raw signals is very large. With the improving of resolution in MFL detecting system, the volume of MFL data also increases. It's obvious that huge data bring about difficulty to the storage and procession. So the effective way to overcome the difficulty is to adopt data compression technique.Wavelet transform coding technique is a fine breakthrough of traditional Sub-band coding. Wavelet decomposition not only gives signal a compact representation, but also provides an effective tool for data compression. A difference between wavelet analysis and traditional Fourier analysis is that the form of representation of Fourier is unique, while the form of wavelet is diversity. The cause is that there are various wavelets, and they have different characters. It provides possibility that specific wavelets are used in the application given. So dealing with the wavelet appropriate to MFL data compression is a very important section.Quantization is a map from many to one. Its purpose is to reduce the kind of symbols for the benefits of following encode section. Many quantization methods with good performance have a large number of calculating operators, which are hard to be implemented by hardware.In this paper noise in high frequency band is removed though quantization based on D L.Donoho's Soft threshold theory. This method not only eliminates measuring noise MFL detecting system but also offer convenience for the following "bit coding". Furthermore this method also has simple operation.Because of the limitation of structure, weight, volume and power of pipeline MFL detecting system, the hardware can't be too complex. Atthe sometime the algorithms of data compressing and acquisition should be relatively simple and mature. So in this paper applied Mallat method, Soft-threshold algorithm, Bit-coding algorithm. At the same time a signal acquisition and compression concurrent execution algorithm is also brought forward. This algorithm has been proved through simulation experiment in laboratory. The experiment system simulates circumstance of oil-gas pipeline and the measurement part, control part, acquisition part, compressing and storage part. It will improve detecting performance and resolution of MFL detecting instrument.