Magnetic measurements magnetization

Sat] Magnetic measurements (magnetic balance) Magnetization, magnetic moments... 

J A measure of the coupling constant in nuclear magnetic resonance. 

Before ehding this presentation on mass spectrometry, we should cite the existence of spectrometers for which the method of sorting ions coming from the source is different from the magnetic sector. These are mainly quadripolar analyzers and, to a lesser degree, analyzers measuring the ion s time of flight. 

A new, non destructive method has been developed for testing high strength bolts which is based on measuring the magnetic stress on the head of a bolt. The forces originating in the body of the bolt can be determined in this way since these forces are proportional to the stress state in the head of the bolt. 

Stress investigation using magnetic Barkhausen noise measurement... 

Typical correlation between the magnetic characteristic and the body force measured on the head of 85 mm long M24 Friedberg 10.9 bolts where the thickness off the plates screwed together is more than 40mm. 

Correlation between the body forces and the stress state in the head was investigated both by the strain gauge method and the optical coat work stress examination method, and the magnetic measurements were performed at the same time. 

During the optical coat work stress examination method the upper plate of the head of some of the bolts was covered with an optical coat work (Fig. 4). On the head of some other bolts strain gauges were stuck which measured the plain biaxial stress state in the middle of the top surface of the head of the bolt (3.5 x 3 mm). The magnetic probe detected average stresses up to 0.1 mm depth in an area of 14 mm diameter in the middle of the head of the bolt. 

It is known that diagram " Stress - Deformation " ( SD) is more vividly specifying the current metalwork condition. However, such diagram can be obtained only by destructive testing. The suggested non-destructive magnetic method in the report for the evaluation of SD condition and for the prediction of residual resource of metalwork, where the measurement of coercive force (CF) is assumed as a basis. 

The suggested method is appropriately implemented at the practice. The cost and working hours of unit measurement of it is less than of any alternative method of destructive test and with respect to the authenticity inspection of Stress-Deformation the given method is inferior only to destructive testing. The method was successfully implemented while evaluation of service life of main pipe-lines sections and pressure vessels as well. Data of method and instrument are used as official data equally with ultrasonic, radiation, magnetic particles methods, adding them by the previously non available information about " fatigue " metalwork structure. 

A SQUID [2] provides two basic advantages for measuring small variations in the magnetic field caused by cracks [3-7]. First, its unsurpassed field sensitivity is independent of frequency and thus dc and ac fields can be measured with an resolution of better than IpT/VHz. Secondly, the operation of the SQUID in a flux locked loop can provide a more than sufficient dynamic range of up to 160 dB/VHz in a shielded environment, and about 140 dB/>/Hz in unshielded environment [8]. 

This algorithm follows the following steps We define the measured map of the magnetic response field matrix A to be ... 

Measuring surface crack depth is performed by calibration samples made of the same material like the object being tested. Calibration samples are the plates having narrow grooves like slits of various depth 0.2 mm, 0.5 mm, 1.0 mm, 2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm and made by electric erosion method. The samples have dimensions 50 mm X 150 mm x 6 mm and 25 mmx 150 mm x 6 mm and are made of magnetic... 

W R McLean. Apparatus for Magnetically Measuring Thickness of Ferrous Pipes US Patent. 6 Nov 51... 

The first equation (1) is the equation of state and the second equation (2) is derived from the measurement process. Finally, G5 (r,r ) is a row-vector that takes the three components of the anomalous ciurent density vector Je (r) = normal component of the induced magnetic field. This system is non hnear (bilinear) because the product of the two unknowns /(r) and E(r) is present. 

In this case, we can conclude that the small sensor is lightly tilted with an angle of 0,25 degrees. We have concluded, during experimentations, that the measurement of the magnetic field is very sensitive to the angle of inclinaison of the sensor. In this way, we validate the computation of the incident field E (r). We can also expect some difficulties for the validation of the forward problem by experimental data. 

In Fig. 3a,b are shown respectively the modulus of the measured magnetic induction and the computed one. In Fig. 3c,d we compare the modulus and the Lissajous curves on a line j/ = 0. The results show a good agreement between simulated data and experimental data for the modulus. We can see a difference between the two curves in Fig. 3d this one can issue from the Born approximation. These results would be improved if we take into account the angle of inclination of the sensor. This work, which is one of our future developpements, makes necessary to calculate the radial component of the magnetic field due to the presence of flaw. This implies the calculation of a new Green s function. 

The INTROS Flaw Detector is able to inspect ropes moving through the magnetic head at speed 0...2 m/s. Limit of sensitivity to wire brake is 1% of the rope meatallic cross-section area, the LMA measure accuracy is not less than 2%. 

The starting point of imaging is the modelisation of the physical process implied when using the sensor once known the exci-tator geometry and the conductivity in any point of the tube, one must be able to compute the magnetic field at any point in the measurement area ... 

It is also necessary to choose the position number and size of sensors to sample the magnetic field with accuracy. As the radial component of this field is null in the median plan of the excitation coil when no flaw is present, it seems obvious to measure this component, so we can use large gain amplifiers, figure 1 shows the typical aspect of the magnetic field for a ponctual flaw when a very long excitation coil is used ... 

The results of measurements and comparisons of the different magnetic field are presented and discussed. Further development will be shown, that this theory can be applied to solve inverse eddy-current problems as well. 

The great variety of inspection applications required the QAP system to perform relative measurements in judgeing certain conditions and not to restrict the user to dictated inspection conditions. One important example for MPI is for example the decision whether the magnetic particle suspension can be used or has to be changed. 

The condition of the magnetic particle suspension is controlled by an automated ASTM-bulb. The bulb is connected to the currently used Magentic particle suspension tank by a bypass, so the suspension in use is flowing through the bulb too. In user defined periods a valve is closed and the Magentic particle suspension remained into the bulb is analysed. The automatic bulb has the ability to measure the extinction and transmission of the suspension related to the time (Figure 1, Figure 2)... 

The system compares its own values for good and a bad magnetic particle suspensions with the actually measured values. The system values are stored in the form of reference curves for a fresh MP-suspension used on the machine and the used MP-suspension which has to be changed. 

In this case the only variation is the magnetization power, measured in Ampere Turn. 

Defect identification, in height and width, is established by tlie magnetization spectrum surfaeic measure, by respecting the latest optimization conditions. The Spectrum sensibility could give us necessary information about the defect depth. 

Measurement by quasi - constant current (steady - state value of pulse current) providing a compete tuning out from the effect of not only electric but also magnetic material properties. 

The method was applied for determination of the quality of the detection media on test pieces following the type testing of the European standard [4] in order to check the validity of the method. The other application was the determination of the visibility in dependance of the variations of the inspection parameters (application of the detection medium, magnetization, inclination, viewing conditions) in a range which may appear in the practical inspections. The results leads to conclusions on the visibility level which is a measure of the probability of recognition for the indication that means of the reliability of the method. 

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