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电容式TP介绍
Capacitive touch screen
Touch screen in accordance with the working principle and information transmission medium, we have divided touch screen into four types, they are resistive, capacitive sensing, infrared and surface acoustic-type. In each category of touch screen has its own advantages and disadvantages, it is necessary to understand which kind of touch screen used for which kind of occasion, the key is to know working principles and characteristics of each type of touch screen technology. Following is the brief introduction of Capacitive touch screen:

1 Touch screen of capacitive technology
To carry out the work by using current sensing of human body. Capacitive touch screen is the four-story complex with a piece of glass screen, glass screen and the inner surface coated with a layer of the laminated ITO, the outermost layer of soil is a thin layer of silicon protective layer of glass, laminated ITO coated as a face, four corners on leads to the four electrodes, the inner layer of ITO as a shield to ensure a good working environment. When the fingers touch the metal layer, due to the human body electric, the user and the touch screen surface with a coupling capacitor, for high-frequency current, the capacitance is a direct conductor; fingers absorb away a very small current from the contact point. The current outflow from the corners of the touch screen of the electrode and the electrode through the four fingers of the current is directly proportional to the distance between the corners, the controller calculate precisely by the four current of the ratio, reached the location of touch points.

2 Defects of capacitive touch screen
The clarity and the light transmission rate of capacitive touch screen better than the four-wire resistive screen, of course, can not compared to the five-wire resistive screen and surface acoustic wave.. Capacitance screen serious reflective, and four-storey complex touch-screen of capacitive technology uneven on the wavelength of light transmittance, there is the problem of color distortion, as a result of light reflection between each floor, but also result in blurred images of characters. Capacitance use the human body as an electrode component of capacitor , when near the conductor amount of capacity sufficient capacitance value which coupling between with interlayer and ITO face ,current flowed away enough caused by capacitor action. . We know that although the capacitance value is inversely proportional to the distance between the Polar, but is proportional to relative size, and also relating with the media the insulation factor. . Therefore, when a larger area of the palm of your hand or hand-held objects close to the conductor rather than capacitive can be caused touching the screen when the capacitive screen mis-operation accrued, in humid weather, this is even more serious, mis-operation capacitance caused by hand-caught monitor, the palm of your hand near the display within 7 cm or body near the display can be caused by less than 15 centimeters of screen. Another drawback of capacitive screens with gloved hand or hand-held non-conductive objects did not respond to touch, which is medium of increasing more insulation. Capacitive screen, which is more important drawback, is that drift: When the ambient temperature and humidity changes, changes in the environment field, the screen would give rise to capacitance drift, resulting in inaccurate. For example: After the boot monitor drift caused by temperature rise: the user touching the screen at the same time the other side of the hand or body will drift around the display; capacitive touch screen near the moving larger objects will cause drift, when you touch them if someone watch also will cause drift; drift of capacitance screen are technical reasons for the deficiencies, although environmental potential surface (including the user’s body) and the capacitive touch screen have a far distance, larger than the number of fingers, they directly affect the determination of the location of the touch . In addition, it should be actually non-linear relationship although linear relationship on the theory, such as: wet weight different or different levels fingers of people sucked out the total amount of current is different, and the total amount of current change and the four sub-Current changes in the relationship between the non-linear, capacitive touch screen used in the four corners of this custom has not polar coordinates of the origin coordinates, the controller can not be detected after the drift and recovery, and after four A / D is completed, by the the value of the four sub-flows to the touch point on the Cartesian coordinate system X, Y coordinates will be the complexity of the calculation process. The absence of starting point, the drift capacitance screen is cumulative, and in the work-site also often requires calibration. Most of the silicon outside of capacitive touch screen, the territories to protect the glass for a good anti-scratch, but fear of a nail or hard object percussion and win a small laminated ITO will be injuried, regardless of injuries or the installation of laminated ITO injured the inner surface of ITO layer during transport so that capacitance on the screen does not work.

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