By knowing the exact runout of these spindles, disc drive manufacturers are able to determine the maximum amount of data that can be placed onto the drives. Capacitive sensors are widely used for measurement of displacement, angle, vibration, speed, pressure, composition analysis, medium characteristics, etc. Capacitance of this capacitor is C=8.854 * 10(–3)*ax,pF, a is the area of the plates, mm2, x is the variable distance between capacitor plates, mm. Capacitive displacement sensors "are non-contact devices capable of high-resolution measurement of the position and/or change of position of any conductive target". So the output voltage between a and b is, Let’s assume that the nominal capacitance of the the variable capacitor is C=εad. 2.2.2.2.3 Capacitive angular displacement sensor. One of the more common applications of capacitive sensors is for precision positioning. A capacitive sensing system for conductive materials uses a model similar to the one described above, but in place of one of the conductive plates, is the sensor, and in place of the other, is the conductive target to be measured. When the preassure on both sides of the capacitors are equal, then capaitances C1 and C2 are equal. [5] In order for this to be effective using a single probe, the parts must be completely flat and measured on a perfectly flat surface. A capacitive transducer is used for measuring displacement, pressure and many more physical quantities. (See the first equation above) By analyzing this change in capacitance, the thickness and density of the non-conductor can be determined. [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 capacitive angular displacement sensor is a precision measurement sensor based on the noncontact capacitive principle. That is, they are able to precisely measure the position or displacement of an object without touching it. It is a passive transducer that means it requires external power for operation. Some are • Flow--Many types of flow meters convert flow to pressure or displacement, using an orifice for volume flow or Coriolis effect force for mass flow. Due to this proportional relationship, a capacitive sensing system is able to measure changes in capacitance and translate these changes in distance measurements. In an motion transducer the capacitor is designed with the variable distance between plates, so one capacitor plate is fixed, and the other is moving, depending on the object position. Capacitance of a parallel-plates capacitor is determined by the formula C=εadwhere a is the plate square, d is a distance between plates, and ε is a permittivity of the material between the plates. [1] They are also able to measure the thickness or density of non-conductive materials. While capacitive displacement sensors are most often used to sense changes in position of conductive targets, they can also be used to sense the thickness and/or density of non-conductive targets as well. For the AC circuit the capacitance of the capacitor, as we stated above, is: where a is the capacitor square with some certain constant, so the capacitor impedance is ZC=1jωC is ZC=xjωa. The gap is often an air gap, (dielectric constant = 1) and the material has a higher dielectric. In electrical engineering, capacitive sensing (sometimes capacitance sensing) is a technology, based on capacitive coupling, that can detect and measure anything that is conductive or has a dielectric different from air. Even for someone who's been exploring capacitive sensing for a week, it's STILL really confusing. Let’s consider the capacitive displacement transducer as a part of an AC circuit. Capacitive displacement sensors can be used to make very precise thickness measurements. These form a type of capacitor. Capacitance is an electrical property which is created by applying an electrical charge to two conductive objects with a gap between them. A simple demonstration is two parallel conductive plates of the same profile with a gap between them and a charge applied to them. Capacitive Transducer Definition: The capacitive transducer is used for measuring the displacement, pressure and other physical quantities. GENERAL SPECIFICATIONS OF INDUCTIVE AND CAPACITIVE SENSORS - EN50032 ACTIVE FACE The active face of proximity sensor is the surface from which emits an oscil-lating field where a metallic object (inductive) or any material (capacitive) results in a change of state of the sensor without entering in contact with it. At other times, they are used to simply look for the presence or absence of a certain component, such as glue. modern capacitive position displacement sensor that currently can measure can measure radial shaft displacement at micrometer level. Capacitive sensors use various types of capacitors as sensing elements. The example is FDC2x1x-Q1, multi-channel family of capacitive sensing solutions by Texas Instruments, which employ the L-C resonator technique. In this situation, the Capacitance can be expressed by the equation: Where C is the capacitance, ε0 is the permittivity of free space constant, K is the dielectric constant of the material in the gap, A is the area of the plates, and d is the distance between the plates. The circuit shown is used for displacement measurement using capacitive sensor, Drive the expression for Vo as a function of the displacement. Capacitive Displacement Sensors – Selection Guide D-510.020 20 to 100 Steel PISeca™ single-electrode capacitive sensor probes Sub-D-510.050 50 to 250 Steel nanometer resolution and excellent linearity, easy setup, D-510.100 100 to 500 Steel extended measurement ranges on request RS UL VO U2 R2 CI HI COMPANY Capacitive displacement sensors measure the shortest ofdistances with highest reliability. 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