Thermostat

A temperature controller is a unit which makes it possible with the aid of a temperature sensor to detect the actual value of a temperature to be compared with a predetermined desired value and an actuator to the desired ( predetermined ) reference value set. A thermostat can be both a temperature controller described as only the temperature sensor without actuator.

Operation

The control loop is used to a predetermined temperature (controlled variable x) to bring to a desired value ( setpoint w ) and keep as constant as possible. To accomplish this task (x = w), the control variable has to be measured with a temperature sensor. Occurs between setpoint and actual value of the controlled variable is a difference on ( error e ), the controller must counteract this. The size has to be changed for this purpose is the manipulated variable ( y). The change of the manipulated variable must lead to a change in the controlled variable. As a result, the deviation is reduced or eliminated completely. The required actuating device consists of the actuator and the actuator, in the case of the temperature controller controls it either a heating element allfällig and cooling element via the power supply (for example, iron), or consists of a controller for an external supply of heat (for example, heater).

An intervention of the temperature controller is triggered either by changing the target size (temperature dial ) or a fault. A fault may be the change in the ambient temperature, for example. It is referred to as a disturbance variable (z). Any change in the disturbance causes a change in the controlled variable. If the disturbance does not change and could find no change in the setpoint takes place, who arrived in the target state temperature controller would remain in this state. The element which carries out the comparison between actual and set value and sets the value for the control means ( control quantity u) is referred to as a controller.

The regulators are often combined in the practice with the sensors and control units in a device or component.

Examples

Thermostats

• Thermostatic valves on radiators and thermostatic mixing valves
• With water or other media working, equipped with a thermostat and a pump devices that are used for thermostating of laboratory setups: Immersion thermostat, bath thermostat. Laboratory thermostats have, in addition to the temperature controller, a pump and a storage vessel for a heat exchange fluid.
• Temperature controller in iron, refrigerators and ovens consist of a temperature switch.
• Thermostat in anesthetic vaporizers ( Vaporen ) in order to keep constant the previously set anesthetic gas concentrations in ambient temperature variations.
• Thermostatically controlled switching of the radiator circuit in the liquid cooling circuit of internal combustion engines.

Complex control systems for the temperature

• Electronic heating control to radiators that have a time of day out temperature setpoint can often be programmed time of day or weekday -dependent and take into account the outside temperature to control the flow temperature (control circuit with several control variables ).
• Self-regulating electric heating elements consist only of a material with an extremely temperature-dependent electrical resistance ( PTC ceramic ) and combine all ingredients in a control loop - the nominal size is a fixed material parameters.
• Electrical temperature controller for industrial applications are often housed in a DIN mount housing and can be configured for a variety of control tasks and characteristics. You can often optional for use with platinum measuring resistors ( Pt100 or Pt1000) or different thermocouples can be configured as a temperature sensor and contain a relay to control a heater or cooler.