| As one of the top five transportation industries,pipeline transportation has many advantages such as continuity,economy,low-loss and strong environmental adaptability.However,with the growth of pipeline age,the damage of pipe wall is inevitable.In order to prevent the safety hidden danger and economic loss caused by pipe wall damage,magnetic leakage flux inspection is used as a common way to find wall damage.As the core device,magnetic sensor plays an important role in damage detection.Compared with Hall Element,fundamental mode orthogonal fluxgate(FM-OFG)has many advantages.After research on present situation of FM-OFG,FM-OFG was fabricated and optimized based on the principle of FM-OFG.At first,FM-OFG was fabricated with a Co-based amorphous wire winded by a single copper enameled wire coil in this paper and the whole circuit was designed..Then,the dependence of sensitivity on the excitation current parameters was studied.The sensitivity of FM-OFG was improved by increasing the AC excitation current and decreasing the DC bias current when the operation frequency approaches the LC resonance frequency.As a result,the best sensitivity was 53.004mV/μT with the measurement range of-51.7 to 51.7μT.Considering the small detection range similar to the earth magnetic field,we introduced two kinds of feedback circuits in FM-OFG to extend the measurement range.With feedback resistor R=7kΩ,feedback circuit with an integrator could make the measurement range expanded about 4.7 times with sensitivity similar to original sensitivity.With a larger R=10kΩ,measuring range could only be expanded to 2 times with feedback circuit without an integrator and sensitivity decreased to 53.8%.Therefore one kind of feedback circuit with an integrator had advantage over another kind without integrator.This paper not only provides an experimental basis for the application of the FM-OFG in magnetic leakage flux inspection,but also provides methods to improve sensitivity and expand the measurement range. |
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