Capacitance Probe Technology

A capacitive sensor measurement system requires three components: a probe to detect any changes in distance to a target by sensing changes in capacitance, driver electronics for converting the changes in capacitance into voltage changes, and a device for displaying and/or recording the voltage changes.

Capacitive sensors can sense both metallic and non-metallic materials and are essential instruments in several industrial automation applications.

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Working Principle

Capacitance can be defined as the ability of a body to store an electrical charge. For example, an electric field can be created by placing two metal plates separated by a gap and passing a voltage to one of the plates. The electric field is created because of the disparity between electric charges that exists on the surfaces of the two plates. The ability of the plates to retain that charge is called capacitance.

The capacitance probe is designed to be a point level indicator. It can resemble a neutron probe or can be modular in structure. The probe is connected to a logger. The sensing head to this probe comprises of an oscillator circuit. The sensing surface of the probe is the plate that is electrified. The other plate is the target. The driver electronics supply a voltage to the sensing surface. The driver electronics are calibrated such that they supply specific voltage changes to match changes in capacitance. The resulting voltage change is then measured.

BinMaster manufactures a range of capacitance probes for various applications. Their PROCAP I & II standard capacitance probes are capable of detecting the presence or absence of material that are in contact with them. They perform detection by sensing minute changes in capacitance, which is caused by the difference in the dielectric constant of the material against the air.

Applications

Capacitance probes can be used in tanks, pipes, bins, silos, chutes, conveyors, and load out hoppers that are used in high temperature environments, hazardous area environments, and high pressure wash-down environments.

The following are some of the applications for capacitance probes:

• Measuring soil water content
• Controlling level of liquids, solids, powders, and slurries
• Detecting pipeline and vessel leaks
• In sanitary food and dairy processing
• In pharmaceuticals manufacturing
• In wood or paper processing
• Monitoring feed hopper level.