How to Test Solenoid Coil?

Figure 1: Solenoid coil.
(Go to Okmarts and pick the Solenoid coil you need)

When selecting and using Solenoid coil, we should think about the inspection and measurement of the coils, and then judge the quality and advantages and disadvantages of them.

1. How to Test It

The accurate test of inductance and quality factor Q of solenoid coil generally requires special instruments, and the test method is complex. In practical work, this kind of test is generally not carried out, we only do the on-off inspection of the coil and the judgment of the Q value.

The DC resistance can be measured with a multimeter and then compared with the nominal resistance. If the measured resistance value is much larger than that, or even the pointer does not move (the resistance value tends to infinity), then we can determine that the coil is broken; If the measured resistance value is very small, this situation is a serious short circuit or local short circuit. When these two conditions occur, it can be determined that the coil is bad, which means it cannot be used. If there is little difference between the measured resistance and the original or nominal resistance, we can judge that the coil is good.

Figure 2: Do the on-off inspection.

In this case, we can judge the quality of the coil, that is, the Q value according to the following situations. The smaller the inductance Q of the coil, the higher the phase resistance; The larger the diameter of the wire used, the larger the Q value; If multi strand winding system is adopted, the more strands of conductor, the higher the Q value; The smaller the loss of the material used in the coil frame (or iron core), the higher its Q value. For example, when high silicon steel sheet is used as iron core, its Q value is higher than that when ordinary silicon steel sheet is used; The smaller the coil distributed capacitance and magnetic flux leakage, the higher the Q value. When the coil has no shield and there are no metal components around the installation position, its Q value is higher. On the contrary, the Q value will be lower. The closer the shield or metal component is to the off-line coil, the more serious the Q value is reduced.

2. Matters

2.1 Inspect The Appearance of The Coil Before Installation

Figure 3: Inspect the appearance of the coil.

We should check whether the structure of the coil is firm; whether the wire turns are loose; looseness of lead contact; whether the magnetic core rotates flexibly, etc. The installation can be carried out after passing the inspection in these aspects.

2.2 Consider The Fine-tuning Method

Some coils need to be fine tuned during use, and it is inconvenient to change the number of coils. Therefore, the method of fine tuning should be considered when selecting. For example, a single-layer coil can use the method of removing the digital trap coil near the end point, that is, 3 ~ 4 turns are wound at one end of the coil, and the inductance can be changed by moving its position during fine adjustment. Practice shows that this adjustment method can realize fine adjustment of ± 2% - ± 3% inductance. For coils used in short wave and ultrashort wave circuits, half a turn is often reserved for fine adjustment. Move or turn this half turn to change the inductance and realize fine adjustment. The fine adjustment of multi-layer segmented coil can be realized by moving the relative distance of one segment. The number of turns of the movable segment should be 20% - 30% of the total turns. Practice has proved that this fine-tuning range can reach 10% - 15%. For a coil with a magnetic core, the coil inductance can be fine tuned by adjusting the position of the magnetic core in the coil tube.

2.3 Pay Attention to Maintaining The Inductance of The Original Coil

Do not change the shape and distance between coils when the coil is in use. Otherwise it will affect the original inductance of the coil. In particular, the higher the frequency the fewer coils. Therefore, the high-frequency coil used in TV is generally sealed and fixed with high-frequency wax or other dielectric materials. In addition, it should be noted that during maintenance, do not change or adjust the position of the original coil at will, so as to avoid detuning fault.

2.4 Installation of Adjustable Coil Should be Right

Figure 4: Adjustable coil.

The adjustable coil should be installed at the easily adjustable position of the machine, so as to adjust the inductance of the coil and achieve the best working state.

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