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A proximity sensor (often simply prox) is a sensor able to detect the presence of nearby objects without any physical contact. A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation ( infrared , for instance), and looks for changes in the field or return signal .
An inductive sensor is a device that uses the principle of electromagnetic induction to detect or measure objects. An inductor develops a magnetic field when an electric current flows through it; alternatively, a current will flow through a circuit containing an inductor when the magnetic field through it changes.
Reed switches can be used to directly switch a variety of loads ranging from nanovolts to kilovolts, femtoamperes to amperes, and DC to radio frequency. Other magnetically-activated switching devices have a limited range of output voltages and currents, and generally do not directly control a final device such as a lamp , solenoid , or motor .
Proximity switches operate by the disturbance of an electromagnetic field, by capacitance, or by sensing a magnetic field. Rarely, a final operating device such as a lamp or solenoid valve is directly controlled by the contacts of an industrial limit switch, but more typically the limit switch is wired through a control relay , a motor ...
Many types of sensors use capacitive sensing, including sensors to detect and measure proximity, pressure, position and displacement, force, humidity, fluid level, and acceleration. Human interface devices based on capacitive sensing, such as touchpads, [1] can replace the computer mouse.
The disadvantages of the knife switch are the slow opening speed and the proximity of the operator to exposed live parts. Metal-enclosed safety disconnect switches are used for isolation of circuits in industrial power distribution. Sometimes spring-loaded auxiliary blades are fitted which momentarily carry the full current during opening, then ...