Hei Inspektører!
Within the use of MFL equipment it is common to hear about sensors or Hall-type elements, but what is this and how does it work?
The Hall element is a solid state sensor that responds in a linear way to the increase in the intensity of the magnetic field that passes through it.
The main advantage of the device is the small size of its active area. Hall effect devices as small as 0.1 by 0.025 mm have been reported to have been used in the evaluation of bearing races, with a sensitivity of 0.5 volts per ampere (tesla (0.05 volts per ampere / kilogauss) of active areas. The second advantage of these devices is that they can be aligned to measure the normal (Hy) or tangential (Hx) component of the flow leakage field of a discontinuity, with an amplitude that does not depend on the speed of the sensor over the discontinuity as is the case with the coils.
The main disadvantage of Hall arrays is that, like many other solid-state devices, no two have exactly the same sensitivity and therefore, when they are used in this type of group arrangement, some time must be spent balancing. electronic fix. Also, because these devices require activation, additional circuitry is needed and, since they are less robust than a coil, they require encapsulation. This protection can often lead to a relatively large lift-off between the Hall element's active area and the inspected surface and the sensitivity is reduced.
Recent advances in solid state technology allow Hall-type elements to be combined with power supplies and amplifiers on a single chip. Such devices also have good temperature characteristics and have been shown to be useful as inspection sensors at elevated temperatures. Outputs of 75 volts per tesla (7.5 millivolts per gauss) are possible with these devices.