Sensor inductive and capacitive proximity

The operation of proximity sensors can be based on a wide range of principles, including capacitance, induction, Hall and magnetic effects variable reluctance, linear variable differential transformer (LVDT), variable resistor mechanical and electromechanical limit switches optical, photoelectric, or fiber-optic sensors laser-based distance, dimension, or thickness sensors air gap sensors ultrasonic and displacement transducers. Their detection ranges vary from micrometers to meters, and their applications include the measurement of position, displacement, proximity, or operational limits in controlling moving components of valves and dampers. Either linear or angular position can be measured ... 

There are three types of prox sensors inductive, capacitive, and magnetic. Inductive proximity sensors are triggered when a piece of metal comes close to the sensor. Inductive sensors are the ones most commonly used for die protection. In this chapter, the term proximity sensor refers to the inductive type unless otherwise noted. 

There are many different combinations of sensors and control valves on production machines. The sensor is usually mounted above the slip in the reservoir behind the doctor blade. In the case of puddle casting, where the slip is pumped onto the carrier behind the doctor blade, there is no reservoir, and the sensor detects the spread of the slip backward from the doctor blade itself. The most common sensors are based upon capacitance or inductance and are known as proximity sensors. These sensors detect the surface of the slip and generate an electrical impulse when the slip is within range. The electrical impulse in turn controls either an on-off valve or a proportional valve to control the flow of slip to the reservoir. When the slip falls below the range of the sensor, the valve automatically opens to allow more slip to flow into the reservoir until the electrical impulse begins the controlling cycle once more. 

Proximity and presence Proximity sensors, motion detectors Optical, capacitive, resistive, inductive. Hall, Doppler, magnetostrictive effect. Infrared sensitivity, microwave, ultrasonics... 

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