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A key switch (sometimes called a keyswitch or lock switch) is a key-operated switch. [1] Key switches are used in situations where access to the switch's functions needs to be restricted. [2] [3] Key switches are available as components with solder connections, and are available with a variety of ampere ratings. They may use tubular or other ...
On–off control uses a feedback controller that switches abruptly between two states. A simple bi-metallic domestic thermostat can be described as an on-off controller. When the temperature in the room (PV) goes below the user setting (SP), the heater is switched on. Another example is a pressure switch on an air compressor.
Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air in a central location such as a furnace room in a home, or a mechanical room in a large building. The heat can be transferred by convection, conduction, or radiation. Space heaters are used to heat single rooms and only consist of a single unit.
Shut-off / On-off valve: These valves are either completely open or closed. Examples: Gate valve, ball valve, globe valve, angle valve, pinch valve, diaphragm valve; Check valve: Allows flow only in a single direction; Steam conditioning valve: Regulates the pressure and temperature of inlet media to required parameters at outlet.
After receiving an operation command, the actuator moves the valve in direction OPEN or CLOSE. When reaching the end position, an automatic switch-off procedure is started. Two fundamentally different switch-off mechanisms can be used. The controls switch off the actuator as soon as the set tripping point has been reached. This is called limit ...
Whenever the kiln power switch is turned on, the key is automatically held by the interlock, and cannot be manually removed. In order to open the kiln door, the power switch must first be turned off, which releases the key and allows it to be removed from the interlock. The key can then be used to unlock the kiln door.
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These sense the air temperature using the differential expansion of two metals to actuate an on/off switch. [14] Typically the central system would be switched on when the temperature drops below the setpoint on the thermostat, and switched off when it rises above, with a few degrees of hysteresis to prevent excessive switching.