# New On-Line MFL Testing Method and Apparatus for Winding Mine Hoist Wire Rope
## 3 Analysis of the Novel Probe  
### Open-Loop Permanent Magnetizer  
In the nondestructive testing of steel wire rope, permanent magnetic leakage detection devices have been widely adopted [14; 15]. The three main types of permanent magnetization sensors for steel wire rope are depicted in Figure 2: (a) a sensor of the magnetic bridge type consisting of multiple independent sets of magnetizers [17; 26]; (b) a sensor with radial magnetization consisting of two semi-annular sets of upper and lower magnetizers [19; 27]; and (c) an open-loop sensor with axial magnetization consisting of upper and lower half-loop magnetizers [25; 28]. Figure 1: Schematic diagram of the working principle of the WMH system. Figure 2: Three types of wire rope permanent magnetization sensors: (**a**) multi-loop magnetic bridge circuit type detection sensor; (**b**) radially magnetized detection sensor; and (**c**) open-loop sensor with axial magnetization. Magnetic pole surfaces of the detection sensors interact with the corresponding wire rope surfaces, resulting in frictional wear to both the measuring probe and high-speed running wire ropes, making it difficult to distinguish between the probe and the wire rope. In order to analyze the magnetic force applied to the wire rope shown in Figure 2, finite element models were constructed of three detection sensors with the same axial length, diameter, and spacing between magnets. The dimensions and properties of the three sensors are summarized in Table 1.  
Figure 3 illustrates three types of sensors on the wire rope force situation. The magnetic force applied to the wire rope by multiple magnetic bridge sensors is densely distributed and has a large value, while the magnetic force applied by the open-loop sensor with axial magnetization is sparsely distributed and has a very small value. In Table 2, the magnetic force components and the total force generated by the different sensors are shown. The total magnetic force generated by the three magnetizers, (a), (b), and (c), is 29.406 N, 73.263 N and 15.439 N; in other words, the open-loop sensor with axial magnetization applies the smallest magnetic force to the wire rope, which permits high-speed operation of the wire rope by reducing friction between it and the sensor. At the same time, the sensor with a larger inner diameter is located far from the surface of the wire rope, thus enhancing its service life. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parts** & **Sizes** & **Material Properties** \\ \hline Wire Rope & & Diameter is 30 mm, \\  & & length is 500 mm. \\ \hline  & Magnets & Length in Z-direction is 30 mm, \\  & Magnets & width in X-direction is 20 mm, \\  & & height in Y-direction is 15 mm. \\ (a) Six sets of identical magnetic & & Length in Z-direction is 120 mm, \\  & & width in Z-direction is 20 mm, \\  & & height in Y-direction is 10 mm. \\  & Distance between the magnet and & 10 mm \\  & the surface of the wire rope & \\ \hline  & Magnets & Inner diameter is 50 mm, \\  & Magnets & outer diameter is 80 mm, \\  & & thickness is 30 mm. \\ (b) Radially magnetized sensor & & Inner diameter is 80 mm, \\  & Magnetic Cores & outer diameter is 100 mm, \\  & & length is 120 mm. \\  & & thickness is 60 mm. \\  & & lower magnetizers & 4 mm \\ \hline  & Magnets & Inner diameter is 70 mm, \\  & & outer diameter is 100 mm, \\  & & thickness is 30 mm. \\ (c) Open-loop sensor with & & Inner diameter is 70 mm, \\  & & outer diameter is 100 mm, \\  & & thickness is 60 mm. \\  & & \\  & & \\ \end{tabular}
\end{table} 
Table 1: Parameters of the finite element model for the detection sensor. The structural configuration and detection principle of the open-loop magnetizer are shown specifically in Figures 4 and 5. An open-loop magnetizer is a split structure composed of two identical axially magnetized rings, probe A and probe B, one of which consists of two magnets and a magnetic core to act as a magnetization circuit. The two magnetized rings are placed in the probe housing and combined to form a single unit.