Capacitive displacement sensor
[2] Capacitive displacement sensors are used in a wide variety of applications including semiconductor processing, assembly of precision equipment such as disk drives, precision thickness measurements, machine tool metrology and assembly line testing.
The other type measures thicknesses of non conductive materials or the level of a fluid.
Since the area of the probe and target remain constant, and the dielectric of the material in the gap (usually air) also remains constant, "any change in capacitance is a result of a change in the distance between the probe and the target.
A sensor for measuring fluid levels works as two capacitors in parallel with constant total area.
Capacitive displacement sensors can be used to measure the position of objects down to the nanometer level.
Capacitive sensors are also used to pre-focus the electron microscopes used in testing and examining the wafers.
In the disc drive industry, capacitive displacement sensors are used to measure the runout (a measure of how much the axis of rotation deviates from an ideal fixed line) of disc drive spindles.
Capacitive sensors are also used to ensure that disc drive platters are orthogonal to the spindle before data is written to them.
Capacitive displacement sensors can be used to make very precise thickness measurements.
This error can be eliminated by using two capacitive sensors to measure a single part.
(See the first equation above) By analyzing this change in capacitance, the thickness and density of the non-conductor can be determined.
But they also can measure the errors arising in the equipment used to manufacture the part, a practice known as machine tool metrology”.
[7] In many cases, the sensors are used to analyze and optimize the rotation of spindles in various machine tools, examples include surface grinders, lathes, milling machines, and air bearing spindles.
[9] Using capacitive sensors to test assembly line parts can help to prevent quality concerns further along in the production process.
