04-05-2012, 02:07 PM
Thermocouple based temperature controller
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INTRODUCTION
A thermocouple is a device consisting of two different conductors (usually metal alloys) that produce a voltage proportional to a temperature difference between either end of the pair of conductors. Thermocouples are a widely used type of temperature sensor for measurement and control[1] and can also be used to convert a heat gradient into electricity. They are inexpensive[2], interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. In contrast to most other methods of temperature measurement, thermocouples are self powered and require no external form of excitation. The main limitation with thermocouples is accuracy and system errors of less than one degree Celsius © can be difficult to achieve.[3]
Working
In this project thermocouple is connected to microcontroller sense temperature continuously and microcontroller display it on LCD
Buzzer is to alert for extra temperature occur
Set point is fixed in programmed in microcontroller if temperature is rise relay will turn on
Thermocouple Any junction of dissimilar metals will produce an electric potential related to temperature. Thermocouples for practical measurement of temperature are junctions of specific alloys which have a predictable and repeatable relationship between temperature and voltage. Different alloys are used for different temperature ranges. Properties such as resistance to corrosion may also be important when choosing a type of thermocouple. Where the measurement point is far from the measuring instrument, the intermediate connection can be made by extension wires which are less costly than the materials used to make the sensor. Thermocouples are usually standardized against a reference temperature of 0 degrees Celsius; practical instruments use electronic methods of cold-junction compensation to adjust for varying temperature at the instrument terminals. Electronic instruments can also compensate for the varying characteristics of the thermocouple, and so improve the precision and accuracy of measurements.
APPLICATION
* * Heat Detectors (Rate of Rise and Fixed Temperature)
* Manual call points or manual pull stations
* Notification appliances (Simplex systems with TrueAlert signals only)
* Responders
* Fire sprinkler system inputs
* temperature measurement for kilns,
* gas turbine exhaust,
* diesel engines,
* and other industrial processes.