Editing Potentiometer (section)

== Membrane potentiometers ==
A membrane potentiometer uses a conductive membrane that is deformed by a sliding element to contact a resistor voltage divider. Linearity can range from 0.50% to 5% depending on the material, design and manufacturing process. The repeat accuracy is typically between 0.1&nbsp;mm and 1.0&nbsp;mm with a theoretically infinite resolution.  The service life of these types of potentiometers is typically 1 million to 20 million cycles depending on the materials used during manufacturing and the actuation method; contact and contactless (magnetic) methods are available (to sense position). Many different material variations are available such as [[Polyethylene terephthalate|PET]], FR4, and Kapton. Membrane potentiometer manufacturers offer linear, rotary, and application-specific variations. The linear versions can range from 9&nbsp;mm to 1000&nbsp;mm in length and the rotary versions range from 20 to 450&nbsp;mm in diameter, with each having a height of 0.5&nbsp;mm. Membrane potentiometers can be used for position sensing.<ref>
[http://www.designworldonline.com/articles/5903/260/Membrane-Potentiometers-Simplify-Position-Sensing.aspx Membrane Potentiometer White Paper]</ref>

For touch-screen devices using resistive technology, a two-dimensional membrane potentiometer provides x and y coordinates. The top layer is thin glass spaced close to a neighboring inner layer. The underside of the top layer has a transparent conductive coating; the surface of the layer beneath it has a transparent resistive coating. A finger or stylus deforms the glass to contact the underlying layer. Edges of the resistive layer have conductive contacts.
Locating the contact point is done by applying a voltage to opposite edges, leaving the other two edges temporarily unconnected. The voltage of the top layer provides one coordinate. Disconnecting those two edges, and applying voltage to the other two, formerly unconnected, provides the other coordinate. Alternating rapidly between pairs of edges provides frequent position updates. An [[analog-to-digital converter]] provides output data.

Advantages of such sensors are that only five connections to the sensor are needed, and the associated electronics is comparatively simple. Another is that any material that depresses the top layer over a small area works well. A disadvantage is that sufficient force must be applied to make contact. Another is that the sensor requires occasional calibration to match touch location to the underlying display. (Capacitive sensors require no calibration or contact force, only proximity of a finger or other conductive object. However, they are significantly more complex.)