Capacitive technology contact screens are operated using the current induction of the human body. The capacitive contact screen is a four-layer composite glass screen, the inner and outer surface of the glass screen and the interlayer are each coated with a layer of ITO, the outermost layer is a thin layer of silica glass maintenance layer, the interlayer ITO coating is used as the working surface, four electrodes are drawn out at the four corners, and the inner ITO is the shielding layer to ensure a good working environment. When the finger touches the metal layer, due to the electric field of the human body, the user and the contact screen form a coupling capacitor, which is a direct conductor for high-frequency currents, so the finger sucks a small current from the contact point. This current is distributed from the electrodes on the four corners of the contact screen, and the current flowing through these four electrodes is proportional to the interval between the finger and the four corners.
Defects in capacitive contact screens
The light transmittance and clarity of the capacitive contact screen are better than those of the four-wire resistive screen, and of course it cannot be compared with the external acoustic wave screen and the five-wire resistive screen. The reflection of the capacitive screen is severe, and the transmittance of the four-layer composite contact screen of the capacitive technology to each wavelength of light is uneven, and there is a problem of color distortion, and due to the reflection of light between the layers, it also forms the blurring of picture characters.
In principle, the capacitive screen uses the human body as an electrode of a capacitor element, and when the conductor is close to the interlayer ITO working surface to couple the capacitance that satisfies the capacitance value, the current flowing away will meet the malfunction of the capacitive screen. We know that the capacitance value, although inversely proportional to the interpolar spacing, is proportional to the relative area and is also related to the insulation coefficient of the dielectric. Therefore, when a larger area of the palm or the hand-held conductor is close to the capacitive screen instead of contacting, it can cause the malfunction of the capacitive screen, and in humid climates, this situation is particularly severe, and the malfunction of the capacitive screen can be caused by holding the monitor, the palm of the hand is close to the display within 7 cm or the body is close to the display within 15 cm. Another defect of capacitive screens is that they do not react when touched with a gloved hand or when holding a non-conductive object, which is due to the addition of a more insulating medium.
The more important defect of the capacitive screen is drift: when the ambient temperature and humidity change, and when the ambient electric field changes, it will cause the drift of the capacitive screen, forming inaccurate. For example, when the temperature of the display rises after powering on, the temperature of the display will drift: when the user touches the screen, the other hand or side of the body approaches the display. Large objects near the capacitive contact screen drift back after moving, and if someone comes around to watch when you touch, it will also cause drifting; The reason for the drift of the capacitive screen is a congenital deficiency of technology, although the environmental electric potential surface (including the user's body) is far away from the capacitive contact screen, it is much larger than the finger area, and they directly affect the determination of the contact orientation. In addition, theoretically, many connections that should be linear are actually nonlinear, such as: the total amount of current sucked by people with different weights or different degrees of finger wetness is different, and the change of total current and the change of four sub-currents are non-linear connections, the custom polar coordinate system of the four corners used by the capacitive contact screen does not have the origin of the coordinates, and the controller can not detect and recover after drifting, and after the completion of the 4 A/D, the value of the four shunts is transferred to the X, The accounting process for Y coordinate values is messy. Since there is no origin, the drift of the capacitive screen is cumulative and calibration is often required on the job site. The scratch resistance of the outermost silica maintenance glass of the capacitive contact screen is very good, but it is afraid of the knocking of nails or hard objects, and knocking out a small hole will hurt the interlayer ITO, whether it is injuring the interlayer ITO or injuring the internal and external ITO layers during the transportation of the device, the capacitive screen will not work normally.
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