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[email protected] crimeahostel@gmail.com is offline
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Default thermostat with adjustable hysteresis?


Not to get picky, but "dead band" is what you really mean, not hysteresis..


http://en.wikipedia.org/wiki/Deadband

Hysteresis Vs. Deadband[edit]
Deadband is different from hysteresis. With hysteresis there is no dead zone, and so the output is always in one direction or another.[clarification needed] Devices with hysteresis have memory, in that previous system states dictate future states.[clarification needed] Examples of devices with hysteresis are single-mode thermostats and smoke alarms.

Thermostats[edit]
Simple (single mode) thermostats exhibit hysteresis. The furnace in the basement of a house is adjusted automatically by the thermostat to be switched on as soon as the temperature at the thermostat falls to 18 °C, for example, and the furnace is switched off by the thermostat as soon as the temperature at the thermostat reaches 22 °C. There is no temperature at which the house is not being heated or allowed to cool (furnace on or off).

A thermostat which sets a single temperature and automatically controls both heating and cooling systems without a mode change exhibits a deadband range around the target temperature. The low end of the deadband is just above the temperature where the heating system turns on. The high end of the deadband is just below the temperature where the air-conditioning system starts.

Alarms[edit]
A smoke detector is also an example of hysteresis, not deadband. The smoke detector at the ceiling of the kitchen starts the alarm as soon as the level of smoke reaches a certain starting value, x, then the smoke detector stays in the alarm position until the level of smoke has been reduced to level y, after which the smoke detector is reset automatically to "normal". The hysteresis here is x minus y.

References[edit]
Johnson, Curtis D. "Process Control Instrumentation Technology", Prentice Hall (2002, 7th ed.)
"Dead Band Plus Hysteresis Estimation with ValveLink Diagnostics". Product Bulletin. Fisher Controls International. October 2012. Retrieved 18 January 2013.
Murty, D.V.S. (2009). Transducers & Instrumentation (2nd ed.). New Delhi: Prentice-Hall of India. pp. 15-16. ISBN 978-8120335691. Retrieved 18 January 2013.
Postlethwaite, Bruce. "On-Off Control". Introduction to Process Control. Department of Chemical and Process Engineering, University of Strathclyde. Retrieved 18 January 2013.