![]() When higher control precision is required, a PID or MPC controller is preferred. Electronic thermostats have an electronic equivalent. When current passes the wire, a small amount of heat is generated and transferred to the bimetallic coil. Bimetallic sensors can include a physical "anticipator", which has a thin wire touched on the thermostat. Turning off exactly at the setpoint will cause actual temperature to exceed the desired range, known as " overshoot". To improve the control performance of the system, thermostats can include an "anticipator", which stops heating/cooling slightly earlier than reaching the setpoint, as the system will continue to produce heat for a short while. Īnother consideration is the time delay of the controlled system. Such control is in general inaccurate, inefficient and high-level mechanical wear, but for components like compressors, it still has a significant cost advantage compared with more advanced ones allowing continuously variable capacity. Instead, there are oscillations of a certain magnitude, usually 1-2 ℃. As a consequence, conventional thermostats cannot control temperatures very precisely. Although it is the simplest program to implement, such control method requires to include some hysteresis in order to prevent excessively rapid cycling of the equipment around the setpoint. Electronic thermostats, instead, use a thermistor or other semiconductor sensor, processing temperature change as electronic signals, to control the heating or cooling equipment.Ĭonventional thermostats are example of " bang-bang controllers" as the controlled system either operates at full capacity once the setpoint is reached, or keeps completely off. ![]() ![]() Mechanical thermostats commonly use bimetallic strips, converting a temperature change into mechanical displacement, to actuate control of the heating or cooling sources. Thermostats use different types of sensors to measure temperatures and actuate control operations. Examples include building heating, central heating, and air conditioners, kitchen equipment such as ovens and refrigerators, and medical and scientific incubators. Thermostats are used in any device or system that heats or cools to a setpoint temperature. A thermostat can often be the main control unit for a heating or cooling system, in applications ranging from ambient air control to automotive coolant control. The word thermostat is derived from the Greek words θερμός thermos, "hot" and στατός statos, "standing, stationary".Ī thermostat exerts control by switching heating or cooling devices on or off, or by regulating the flow of a heat transfer fluid as needed, to maintain the correct temperature. Sometimes a thermostat combines both the sensing and control action elements of a controlled system, such as in an automotive thermostat. Ī thermostat operates as a "closed loop" control device, as it seeks to reduce the error between the desired and measured temperatures. Thermostatically controlled loads comprise roughly 50% of the overall electricity demand in the United States. In scientific literature, these devices are often broadly classified as thermostatically controlled loads (TCLs). Examples include building heating, central heating, air conditioners, HVAC systems, water heaters, as well as kitchen equipment including ovens and refrigerators and medical and scientific incubators. A Honeywell electronic thermostat in a retail storeĪ thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.
0 Comments
Leave a Reply. |