However, the known limitations of such apparatus (the integral evaluation of the cross-section properties of the products under test, quite high requirements for aligning of the product inside the transducer, the high sensitivity to the structural inhomogenities of the product metal, decreasing the sensitivity to the defects with increasing of the product diameter, etc. ) demand the further improvement of the through type transducers.

In this work some methods aimed at further improvement of the transducers of this type are described.

1. The method of suppression of noise from the structural inhomogenities of metal.

   These are the cases when noises remain quite high after using the known method of suppression by means of longitudinal magnetizing of the product with the permanent magnetic field.

   The method proposed is based on using the additional measuring channel formed by the additional measuring winding the diameter of which is large relative to the primary winding.

   Non-linear system of equations appears:

   U₁=f₁ (d_g, w, µ, , r_n1)

   U₂=f₂ (d_g, w, µ, , r_n2)

   where d_g - is the size of the defect, w - is the frequency of the excitation current, µ- the magnetic permeability of the product metal, - is the electric conductivity of metal, r_n1, r_n2 - is the radii of the measuring windings.

   In signals suppression a signal from defect is distinguished as a result of less sensitivity to the defect of the second measuring winding of the transducer.

2. The method of electronic following up the position of the product inside the transducer.

   This method is based on forming four measuring channels, in each one the amplitude of the signal from a defect is adjusted depending on the distance between the measuring winding and the article checked by introducing the four channels measuring this distance. The channels are formed by four measuring windings of through type. The peculiar feature of these windings is their unequal sensitivity to defects at the angular coordinate. For each winding the sector is distinguished equal about to the third part of the circle of the cross-section of increased sensitivity to the defects. The angular sensitivity non-symmetry of the through type winding is provided by the split metal screens.

   The methods described were implemented in the industrial defectoscope B -40introduced in a number of the tube works of Russia. The positive results of the methods are particularly noted in testing the tubes made of the alloyed steels having high level of noises from the structural inhomogenities of metal (for example, stainless steels with magnet-phase) and also the tubes of high curvature.

   While the reliability of testing of such tubes by the traditional defectoscopes with through type transducers was in a number of cases below 0.5 (i. e. below the allowable level), it was 0.85- 0.90 for the defectscopes B-40. In measuring the clearance between the measuring winding and the product within ± 3 mm (per radius) the signals from the defects were defined accurate to 10% of the measured value. In using the usual defectoscopes the signal from the defect is changing three and more times.