The difference between nickel-zinc ferrite core and manganese-zinc ferrite core
Manganese-zinc ferrite cores and nickel-zinc ferrite cores are two major series of magnetic core components with many varieties and wide applications in the soft ferrites currently produced. We know that U-shaped magnetic cores, deflection magnetic cores, and E-shaped magnetic cores used as transformers in TV sets are generally made of manganese-zinc ferrite materials. Magnetic antennas used in radios are either manganese-zinc or nickel-zinc, but they can be distinguished by different colors of the rod end. For example, some factories spray black paint on the end of the manganese-zinc medium-wave magnetic rod, and spray big red paint on the end of the nickel-zinc short-wave magnetic rod. In addition, various toroidal cores are also divided into manganese-zinc and nickel-zinc.
However, when encountering smaller thread-shaped, cylindrical, I-shaped and hat-shaped magnetic cores, some are made of manganese-zinc materials, and some are made of nickel-zinc materials, and there is no color code on the magnetic core. How to distinguish when magnetic cores are mixed together? Two specific methods are described below.
1. Visual inspection method: Generally, the magnetic permeability of Mn-Zn ferrite magnetic ring is relatively high, the crystal grain is larger, and the structure is relatively compact, and it is often black. The nickel-zinc ferrite magnetic ring generally has a relatively low permeability μ, fine and small crystal grains, and a porous structure, which is often brown, especially when the sintering temperature is relatively low during the production process. According to these characteristics, we can distinguish them by visual inspection. In a brighter place, if you see the ferrite's color is black and there are more dazzling bright crystals, this magnetic core is manganese-zinc ferrite; if you see the ferrite with brown color, dim gloss, and no crystal grains Dazzling, this magnetic core is nickel-zinc ferrite. Visual inspection is a relatively rough method, and it can be mastered after certain practice.
2. Test method: This method is more reliable, but it needs some test instruments, such as high resistance meter, high frequency Q meter, etc.
1. Use the different resistivity ρ of manganese-zinc and nickel-zinc ferrite to distinguish. Because the resistivity of manganese-zinc ferrite is relatively low, about 103Ω·cm or less, while the resistivity of nickel-zinc ferrite is relatively high, about 105-108Ω·cm. Therefore, we can use a high resistance meter or any other meter that can measure resistivity. Before testing, make two electrodes at any position on the magnetic core. For the convenience of testing, two cylindrical end faces of threaded, cylindrical, and I-shaped magnetic cores can be selected as electrodes. Cap-shaped magnetic cores can be used as two electrodes on the same circular plane. At this time, use sand skin to lightly grind away the oxide layer of the magnetic core of the part to be tested, and then coat the material with good conductivity as the test electrode. Generally, you can coat two graphite electrodes with a 6B pencil to make a cylinder as shown in Figure 2. The graphite electrode shown in the shape core and the hat shape core measures the resistivity when the DC voltage is more than tens of volts. After making the two graphite electrodes, you can also use a 500-type multimeter (the range selection switch can be placed in the 10K gear) to measure the resistance of the magnetic core to distinguish between manganese-zinc and nickel-zinc ferrite. Generally, the resistance value below 150KΩ is manganese-zinc; the resistance value is quite large, and the pointer of the multimeter head is basically fixed is the nickel-zinc ferrite magnetic ring.
2. We can also use the different frequency f of manganese-zinc and nickel-zinc ferrite magnetic rings to distinguish. Since the frequency of use of Mn-Zn ferrite bead is generally below 2 MHz, its Q value is low; while the frequency of use of Ni-Zn ferrite bead is 2 to 200 MHz, and its Q value is higher. We can use ready-made high-frequency coils, such as the one shown in Figure 3 (when the coil is not equipped with a magnetic core, the inductance is less than 20μH), first take out the magnetic core, and then install the ferrite core to be tested separately. Measure the Q value on the QBG-3 high-frequency Q meter or other instruments with the same accuracy. The high Q value is nickel-zinc; the low Q value (generally several times lower) is manganese-zinc.