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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 contactor ...
Switches can be designed to respond to any type of mechanical stimulus: for example, vibration (the trembler switch), tilt, air pressure, fluid level (a float switch), the turning of a key , linear or rotary movement (a limit switch or microswitch), or presence of a magnetic field (the reed switch). Many switches are operated automatically by ...
Examples of devices providing a discrete signal include limit switches and photoelectric sensors. [26] Analog signals can use voltage or current that is analogous to the monitored variable and can take any value within their scale. Pressure, temperature, flow, and weight are often represented by analog signals.
The safety benefit of reducing the power delivered to a short circuit in the load is proportional to the operating current limit. Foldback current limiting is most likely to be found in a switch-mode power supply when it is a component in a product that is independently certified to meet regional safety standards. [2]
The limit switches signal when an end position has been reached. The torque switching measures the torque present in the valve. When exceeding a set limit, this is signaled in the same way. Actuators are often equipped with a remote position transmitter which indicates the valve position as continuous 4-20mA current or voltage signal.
A motor-driven cam (usually relatively slow-speed) and one or more micro switches form a timer mechanism. The snap-switch mechanism can be enclosed in a metal housing including actuating levers, plungers, or rollers, forming a limit switch useful for control of machine tools or electrically-driven machinery.