Process is a natural or artificial progressive continually operations consisting of series of control actions or relatively fixed, successive and gradual changes leading towards a particular result.
process control involves the measurement of the values of a controlled variable and applying manipulated variables to the system to limit or correct the deviation of measured value from a desired value. This serves in system modeling in response of system .
Types of process control
Considering the diagram below
- Open loop process control: the measurement of the output and feed back is not measured in reference to the set point. From the diagram above, the ratio of the feedback B(s) signal to the actuating error signal is known as the open loop transfer function. It given as
- Closed loop process control: here the output is measured with reference to the input signal it has a feedback controller. It’s transfer function is related to system dynamics to the dynamics of feed forward element and feedback elements. The transfers function is given as
This is the traditional way of controlling a process. Feedback control system prescribes a relationship between the output and reference input of the control system, this is done by determining the difference between them. It can be also be called a close loop system.
Feed forward control
This detects a disturbance in the system and helps to reassign changes made in the manipulated variable; controlled variable is at constant state.
This compares the difference between the output and the reference input value, uses the deviation and produce a signal that will minimize the error. The method in which the automatic controller produces signal is known as “control action”. It makes use of a sensor which converts the output signal to a suited variable. It can be classified according to control actions as:
- Two position
- Proportional controllers
- Integral controller
- Proportional plus integral controllers
- Proportional plus derivative controller
- Proportional plus integral plus derivative controller