The defect of capacitive touch screen

- Dec 13, 2018-

Defects in capacitive touch screens: 

The transmittance and clarity of capacitive touch screens are superior to those of four-wire resistor screens, and of course cannot be compared with surface acoustic screens and five-wire resistor screens. The reflection of capacitive screen is serious, and the light transmittance of each wavelength is not uniform by the four layer compound touch screen of capacitance technology, and there is the problem of color distortion. 

Because of the reflection of light in each layer, the image character is blurred. In principle, the human body is used as an electrode of a capacitor element. When a conductor is near and coupling with the interlayer ITO face to produce a capacitance of sufficient capacity, the current is enough to cause the error of the capacitor screen. We know that the capacitance value is inversely proportional to the distance between the poles, but it is proportional to the relative area and is also related to the insulation coefficient of the dielectric. Thus, when a larger palm or handheld conductor is close to the capacitor screen rather than touching it, it can cause the screen to misbehave, especially in humid weather, where the display is held by the hand. Hand close to the display within 7 cm or the body close to the display within 15 cm can cause capacitive screen error. 


Another drawback of the capacitor screen is that it does not react when touching with a glove-wearing hand or a handheld non-conductive object because of the addition of more insulating media. The main drawback of capacitor screen is drift: when the environment temperature and humidity change, when the environment electric field changes, it will cause the drift of capacitance screen and cause inaccuracy. For example, when the display temperature rises after boot, it will drift: the user will touch the screen while the other hand or side of the body will drift near the display; The larger object near the capacitive touch screen will cause drift after moving, and if someone comes round to watch it, it will also cause drift. Although the environmental potential surface (including the user's body) is far away from the capacitive touch screen, it is much larger than the finger area, which directly affects the measurement of the touch position. In addition, many of the relationships that should be linear in theory are actually nonlinear, such as the fact that people with different weights or different degrees of finger wetting have different total currents. The change of the total current and the change of the four current are nonlinear. The custom polar coordinate system of the four angles used in the capacitive touch screen has no origin on the coordinate, and the controller can not detect and recover after drift. After the completion of four A- / D, the calculation process from the value of four points of flow to the value of XY coordinate of touch point in right angle coordinate system is complicated. Since there is no origin, the drift of the capacitor screen is cumulative and is often calibrated in the work site. The silicon glass on the outermost side of the capacitive touch screen has good scratch resistance, but if you knock out a small hole in your fingernail or hard object, it will hurt the interlayer ITO, whether it's a sandwich ITO or a ITO layer on the inner surface during the installation process. The capacitor screen will not work properly.