Easy xLogic, User Manual

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Basic concepts of regulating
In the example, the current for the electric heating is the manipulated variable. The changeable
resistance is the actuator. The hand that operates the actuator is the control. The actual room
temperature is the controlled variable or the process value. The desired room temperature is
the command variable or the setpoint value. The electric heating is the control process. The
thermometer is the sensor. The temperature loss from opening the window is the disturbance
variable.
So this means that the person measures the process value (room temperature) with the sensor
(thermometer), compares the process value (room temperature) with the command variable
(desired room temperature) and uses the actuator (changeable resistance) to manually
regulate the manipulated variable (heating current), in order to compensate for the
disturbance variable (temperature drop from opening the window). The person is therefore the
controller.