Understanding the difference between capacitive and eddy-current sensors begins by looking at how they are constructed. At the center of a capacitive probe is the sensing element ultrasonic sens. This piece of stainless steel generates the electric field which is used to sense the distance to the target. Separated from the sensing element by an insulating layer is the guard ring, also made of stainless steel. The guard ring surrounds the sensing element and focuses the electric field toward the target. All of these internal assemblies are surrounded by an insulating layer and encased in a stainless steel housing. The housing is connected to the grounded shield of the cable.

The primary functional piece of an eddy-current probe is the sensing coil. This is a coil of wire near the end of the probe. Alternating current is passed through the coil which creates an alternating magnetic field; this field is used to sense the distance to the target. The coil is encapsulated in plastic and epoxy and installed in a stainless steel housing. The epoxy covered up coil extends from your stainless steel real estate to permit the complete sensing niche to take part the target, considering that magnetic arena of an eddy-most recent detector is not actually as quite simply on target to be the electric powered field of operation to a capacitive sensor.

Spot Size, Target Size, and Range

Capacitive sensors use an electric field for sensing. This field is focused by a guard ring on the probe resulting in a spot size about 30% larger than the sensing element diameter. A typical ratio of sensing range to the sensing element diameter is 1: 8. This means that for every unit of range, the sensing element diameter must be eight times larger. For example, a sensing range of 500µm requires a sensing element diameter of 4000µm (4mm). This ratio is for typical calibrations. High-resolution and extended-range calibrations will alter this ratio.The sensing field of a noncontact sensor's probe engages the target over a certain area. The size of this area is called the spot size. The target must be larger than the spot size or special calibration will be required.Spot size is always proportional to the diameter of the probe. The ratio between probe size and notice size is significantly different for capacitive and eddy-current sensors. These different spot sizes result in different minimum target sizes.

When selecting a sensing technology, consider target size. Smaller targets may require capacitive sensing. But if the focus is required to be smaller compared to the sensor's place dimensions, exceptional calibration could probably make up for the natural measuring problems.Eddy-ongoing detectors use magnetic job areas that 100 % encompass the conclusion of that probe. This creates a comparatively large sensing field resulting in a spot size approximately three times the probe's sensing coil diameter. For eddy-current sensors, the ratio of the sensing range to the sensing coil diameter is 1: 3. This means that for every unit of range, the coil diameter must be three times larger. In this case, the same 500µm sensing range only requires a 1500µm (1.5mm) diameter eddy-current sensor.