Reliability Analysis And Fault Diagnosis Of Borehole Magnetic Measurement Systems

The growing threat posed by earthquakes.A large amount of data shows that as the generation of earthquakes is well correlated and regular with the changes in the geomagnetic field.The occurrence of earthquakes can be predicted by magnetic anomalies.The advantage of borehole magnetic measurement,unlike the surface magnetic measurement environment,is that it reduces magnetic interference,but requires a higher level of instrument reliability.If a magnetic measurement instrument fails during a long-term magnetic measurement in a well,the loss of the magnetic measurement task can be huge,so it is necessary to carry out reliability analysis and fault diagnosis research on the borehole magnetic measurement system.The main research work of this paper has three main aspects.Firstly,the study of the reliability of borehole magnetic measurement systems introduces the characteristic quantities of reliability and the calculation of the corresponding characteristic quantities in the reliability block diagram model.Failure rates are calculated for components and assemblies that are prone to failure in the inwell magnetometer system.The failure rate is tested on the early stage of the development of the system and it is concluded that the failure rate of the system increases and the reliability decreases with time.A reliability block diagram is created for the borehole magnetometer system and the reliability characteristics of each unit are calculated.Secondly,this paper classifies the faults that occur in the borehole magnetometer,describes the faults that occur in the magnetometer system consisting of the light pump total field magnetometer,the fluxgate three-component magnetometer and the rotating magnetic gradient tensor,and analyses the causes of these faults.The failure data of the magnetometer system often comes from experimental testing and development processes or from the use of the site.Under normal conditions of use,some components have a long life span,so temperature and vibration failure acceleration tests have been designed for the magnetometer to identify the components that have suffered losses and failures as quickly as possible and to verify the limits of the instrument under the conditions of use.The characteristics are summarized as pulse,step and ramp faults.Finally,fault diagnosis methods are designed for known fault data characteristics.The Kalman filtering algorithm is used to obtain measurement information and compare it with the information calculated by the corresponding system model to obtain the residuals.The data is verified by means of the magnetic measurement fault data,which shows that the mean value of the residuals is significantly larger when step faults and ramp faults occur,with a difference of an order of magnitude,and that the variance of the residuals is significantly larger when pulse faults and step faults occur.This allows a judgement to be made as to whether a fault has occurred in the magnetometer system.In response to the fact that the helium lamp and the helium absorption chamber in the light pump magnetometer probe always fail to excite,a probe fault diagnostic device was designed to further locate where the fault occurs.The reliability analysis and fault diagnosis work in this paper has proven to be useful in improving the reliability of magnetic measurement instruments and providing some reference for other in-well measurement instruments.