What is a variable capacitor and how to detect and repair it?

Last Update Time: 2018-12-17 13:45:02

1.The capacitor that can be adjusted is called a variable capacitor. The variable capacitor can be divided into air medium and organic film medium according to different media. According to the different structure, it can be divided into single variable capacitor ,double variable capacitor and quadruple variable capacitor.


( 1 ) Single variable capacitor. The single variable capacitor is composed of a set of movable plates, a set of fixed pieces and a rotating shaft. Single variable capacitor film is used as a medium, and the moving sheet and the stator are sealed with a plastic shell, so the sealed single variable capacitor is called a variable capacitor. The air is used as the medium in the single variable capacitor, so it is called the air single variable capacitor. When rotating the rotating shaft, the relative position of the moving piece and the fixed piece is changed, and the capacitance of the capacitor is adjusted. The moveable piece group is all screwed out, and the capacitance is the smallest; the moveable piece group is all screwed, and the capacitance is the largest. For example : 7 / 270p, which means that when rotating the rotating shaft, the capacity of the single variable capacitor can be varied between 7-270pF, so the minimum capacity of the capacitor is 7pF the maximum capacity is 270pF.


( 2 ) Double variable capacitor dual variable capacitor consists of two sets of moving pieces, two sets of fixed pieces and a rotating shaft. As the motion piece of the dual variable capacitor is installed on the axis of the same root, the two groups of capacitance can be adjusted at the same time when the rotating shaft is rotating.


(3) the quadruple variable capacitor quadruple variable capacitor consists of four sets of variable capacitors, which consist of four variable capacitors. When the rotating shaft is rotated, the four capacitors change synchronously when adjusting.


2.Variable capacitor detection


(1) check whether the rotating shaft is flexible to rotate the shaft with the hand lightly. It should feel very smooth, and it should not be loose, tight or even stuck. When the shaft is pushed forward, backward, up, down, left and right, the shaft should not be loosened.


(2) check whether the connection between the rotating shaft and the movable piece is good and reliable

Rotate the rotating shaft and lightly press the outer edge of the film group. No loose phenomenon should be felt. The variable capacitor with bad contact between the rotating shaft and the moving piece can not be used.


(3) check whether there is a short circuit or electric leakage between the moving piece and the fixed piece.

The pointer type multimeter is placed in the RX10k2 block, and the two forms are respectively connected to the movable film of the variable capacitor and the lead end of the fixed piece. The rotating shaft is slowly swirled back and forth, and the multimeter pointer should not move in the infinite position. In the process of rotating shaft, if the pointer sometimes points to zero, it indicates that there is a short circuit point between the blade and the fixed piece. If it turns to a certain angle, the reading number of the multimeter is not infinite but a certain value, which indicates that there is a leakage between the movable film and the film of the variable capacitor.

For dual or multi variable capacitors, the same method can be used to detect other moving parts and fixed parts phenomenon of short circuit or leakage of no collision.


3.Repair the variable capacitor after damage.

The main fault of the variable capacitor is the collision between the moving piece and the fixed piece, the leakage static induction, the loose moving piece, and the malfunction of the moving piece positioning, it can be properly repaired according to different situations.


(1)sealed variable capacitor moving piece and fixed piece collision ( film damage ), you can remove the nuts on the four fixed columns, and then remove the damaged film, put on a good ( can be scrapped from the same type of variable capacitor to remove the use of the film) can be.


(2) sealed variable capacitance in the long-term use of the film medium easy to generate static induction, the adjustment occurs when the " Kaka " noise, the general use of alcohol to clean. However, due to the strong volatility of alcohol, after cleaning for a period of time, it will accumulate static electrons on the film, and the regulation will still produce noise. The better solution is : remove the plastic cover, use a clean lubricant, and spray lubricant at the edge of rotation, so as to avoid electrostatic induction for a long time noise. If the rotating medium is touched by a fixed piece, a thin steel sheet can be used to adjust the deformation of the movable piece.


(3) When the variable capacitor in the air medium is used for too long, dust and oil are accumulated between the sheets, or the moving piece and the fixed piece are corroded, and the surface layer is oxidized, peeling, stained with dirt, and damp, so that the insulation resistance between the fixed piece and the moving piece is decreased, and the film between the fixed piece and the moving piece can not be used normally. In this case, the thin steel sheet is inserted between the human slices, and the dust and the oil stain are removed, and the bumps can be corrected.


If you want to know more, our website has product specifications for variable capacitors, you can go to Allicdata Electronics Limited to get more information.