ET13.pdf

This differentiation can be used as a basis for

This preview shows page 20 - 22 out of 31 pages.

This differentiation can be used as a basis for sorting. In Fig. 21, the shaded symbols represent the controls that are adjusted during each step of setup. As shown in Fig. 21a, a sample of steel A placed in the test coil causes a pattern to appear on the screen. The phase shifter and coarse sensitivity are adjusted until the entire pattern is displayed and centered. A fine sensitivity adjustment is used to bring the curve to a specific indication height called the absolute value. This adjustment lets all positions on the sensitivity selector be expressed as percentages of absolute value. If a second sample A 1 of steel A (Fig. 21b) is placed in the unoccupied difference coil and the sensitivity control is adjusted to a higher level, then a difference between the magnetic properties of samples A and A 1 will appear on the screen as indicated by the solid line in Fig. 21b. If A is then replaced by sample B 1 , a curve for this sample might be as indicated by the broken line in Fig. 21b. Next, sample A 1 is reinserted in the difference coil, replacing B 1 , and the compensator is adjusted so that curve A 1 becomes a horizontal, 340 Electromagnetic Testing F IGURE 21. Operating procedures and screen displays obtained when sorting two steels of composition A and composition B: (a) after phase and sensitivity adjustments; (b) second sample B 1 introduced; (c) sample A reintroduced; (d) curve B 1 centered; (e) curve A 1 symmetrically displaced; (f) amplification. Shaded symbols represent adjusted controls. Screen images show variation of permeability with magnetization (relative scale). (a) Sample A Compensator Amplifier Phase shifter (b) Sample A Sample B 1 Compensator Amplifier Phase shifter (c) Sample A Sample A 1 Sample A Sample B 1 Compensator Amplifier Phase shifter (d) Sample A Sample B 1 Compensator Amplifier Phase shifter (e) Sample A Sample B 1 Compensator Amplifier Phase shifter (f) Sample A Sample B 1 Compensator Amplifier Phase shifter Sample A 1 Sample A
Image of page 20

Subscribe to view the full document.

straight line (Fig. 21c). In the next step, curve B 1 is displayed by the phase shifter so that its peak or maximum lies in the center of the screen (Fig. 21d). In Fig. 21e, curve A 1 is symmetrically displaced downward with reference to curve B 1 by using the compensator. Finally the amplifier is turned up so that the area of the screen is fully used (Fig. 21f). Spread Bands When a large number of samples representing two steels of different chemical composition are sorted, minor variables in samples of the same steel result in a spread band or slight variations to either side of the principal curve. Slight differences in internal stresses or surface decarburization are among the factors that account for these variations. Typical spread bands made with identical instrument settings are shown in Fig. 22 for carbon steel and a sulfurized free machining steel. The bands shown in Fig. 22 reflect the spread obtained when 1000 samples of each steel were tested.
Image of page 21
Image of page 22
  • Fall '19
  • Magnetism, Magnetic Field, Electrical conductivity

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern