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2. HVAC control system - Wikipedia

   en.wikipedia.org/wiki/HVAC_control_system

   Eventually, the relays became electronic switches, as transistors eventually could handle greater current loads. By 1985, pneumatic controls could no longer compete with this new technology although pneumatic control systems (sometimes decades old) are still common in many older buildings. [8] By the year 2000, computerized controllers were common.

3. Key switch - Wikipedia

   en.wikipedia.org/wiki/Key_switch

   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 ...

4. Control system - Wikipedia

   en.wikipedia.org/wiki/Control_system

   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.

5. Bang–bang control - Wikipedia

   en.wikipedia.org/wiki/Bang–bang_control

   In control theory, a bang–bang controller (hysteresis, 2 step or on–off controller), is a feedback controller that switches abruptly between two states. These controllers may be realized in terms of any element that provides hysteresis. They are often used to control a plant that accepts a binary input, for example a furnace that is either ...

6. Central heating - Wikipedia

   en.wikipedia.org/wiki/Central_heating

   The heating elements activate one at a time to avoid overloading the electrical system. Overheating is prevented by a safety switch called a limit controller or limit switch. This limit controller may shut the furnace off if the blower fails or if something is blocking the air flow.

7. AOL Mail

   mail.aol.com

   Get AOL Mail for FREE! Manage your email like never before with travel, photo & document views. Personalize your inbox with themes & tabs. You've Got Mail!

8. Thermostat - Wikipedia

   en.wikipedia.org/wiki/Thermostat

   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.

9. Missing hiker attempting to climb Mount Whitney in California ...

   www.aol.com/missing-hiker-attempting-climb-mount...

   A hiker, who was reported missing in California's Sierra Nevada mountains in the last week of December, was found dead at an elevation of 12,000 feet, officials say. "At this time, no further ...