Capacitive proximity sensors, sometimes referred to as capacitive proximity switches, are ON/OFF output devices that are used to detect the presence of an object at a specific distance or the presence of material in front of the sensor. These sensors can detect the presence of objects through non-conductive containers such as cardboard boxes, and plastic or glass vessels. While some applications benefit from the sensor being in direct contact with the material you wish to detect (like in level applications) it is not always necessary.
Capacitive sensors work by measuring the dielectric of the material around the sensor. This dielectric value increases both when there is more material in front of the sensor and the closer that the material gets to the sensor. This means that capacitive sensors work differently than inductive proximity sensors. Capacitive sensors can detect virtually any material whereas inductive sensors are designed to sense only ferric materials. Capacitive sensors are indifferent to color and work with both liquids and solids. http://www.rechner.com
Unlike capacitive proximity sensors, probe style level sensors are designed specifically to be in direct contact with the target material. Once the level in your container has reached a specified height, the sensor will switch and provide an electrical signal that can be used to control your equipment or sound an alarm. Level applications often have more than one level detection requirement (i.e. high and low-level detection) or require continuous level measurement with an analog sensor. Applications for these sensors are diverse, ranging from small vessels where the height of the material only changes by a fraction of an inch – up to large filling hoppers more than 6 feet tall. http://www.rechner.com