Bioreactor control system

Bioprocess engineering

1. Bioprocess engineering Bioreactor control system 17 September 2019 Bioprocess Engineering 1 Presented by S.Nandhini G.Mohana priya G.Nantha kumar

2. Content : Control system Manual control Automatic control Two-position controller Proportional control Integral control Derivative control Combination of method of control Controller. 17 September 2019 Bioprocess Engineering 2

3. Control systems The process parameters may be controlled using control loops . It consists of four basic components : A measuring element A controller A final control element The process to be controlled . 17 September 2019 Bioprocess Engineering 3

4. Control system Simplest type of control loop : Feedback control In this system output is measured and compared with input reference signal . 17 September 2019 Bioprocess Engineering 4

5. i.e., the measuring device senses a process then generates corresponding output signal . The controller compares the measurement signal with the set point and produces an output signal . The controlling element receives the control signal and adjust the process by changing the valve . Opening or pump speed cause the controlled process to return to the set point . 17 September 2019 Bioprocess Engineering 5

6. Manual system A simple example of control : Manual control . To regulate the temperature of water flowing through a pipe . Manual control may be very costly in terms of labor . So use Automatic control as much as possible . 17 September 2019 Bioprocess Engineering 6

7. Manual control 17 September 2019 Bioprocess Engineering 7

8. Automatic control When an automatic control loop is used, certain modification is necessary . The measuring element must generate an output signal which can be monitored by an instrument. In temperature control, thermometer is replaced by a thermocouple which is connected to a controller which in turn will produce a signal to operate the steam valve. 17 September 2019 Bioprocess Engineering 8

9. Automatic control 17 September 2019 Bioprocess Engineering 9

10. Automatic control systems can be classified into four main types : Two-positions controllers ( ON/OFF). Proportional controllers . Integral controllers . Derivative controllers . 17 September 2019 Bioprocess Engineering 10

11. Two-position controllers(ON/OFF) Two-position controller is the simplest automatic controller : it has a final control unit(valve, switch etc.,) which is either open(ON) Or fully closed(OFF). The response pattern to such a change : oscillatory . Oscillatory pattern of a simple two-position valve or switch : 17 September 2019 Bioprocess Engineering 11

12. It is important to establish that the maximum and minimum valves are acceptable for the specific process, and to ensure that the oscillation cycle time does not cause excessive use of valves or switches. This picture represent Oscillatory pattern of the temperature of a domestic water tank using ON/OFF control of the heating element . 17 September 2019 Bioprocess Engineering 12

13. ON/OFF control is not satisfactory for controlling any process parameter so there is a sudden changes from the equilibrium. In these cases alternative forms of automatic control must be used such as Proportional control Integral control Derivative control Many of the chemical industries are pneumatic. Pneumatic controllers are still widely used because they are robust . In other cases, when the control is electronic , the response to an error will be represented as a change in output current or voltage. 17 September 2019 Bioprocess Engineering 13

14. Proportional control The change in output of the controller is proportional to the input signal produced by the environmental change (error) which has been detected by a sensor . Mathematically it can be expressed by the following equation: M=M0+Kc Σ where, M = output signal Mo = controller output signal when there is error . Kc = controller gain or sensitivity Σ = the error signal . 17 September 2019 Bioprocess Engineering 14

15. The term Kc is the multiplying factor which relates a change in input to the change in output . Where, Kc may contain conversion units This quantity PB is the error required to move the final control element over the whole of its range and is expressed as a percentage (%) of total range of measured variable . 17 September 2019 Bioprocess Engineering 15

16. Integral control The output signal of an integral controller is determined by the integral of the error input over the time of operation . Where Ti = integral time . it is important to remember that the controller output signal changes relatively slowly at first as time is required for the controller action to integrate the error . 17 September 2019 Bioprocess Engineering 16

17. Derivative control The controller senses the rate of change of the error signal and contributes a component of the output signal that is proportional to a derivative of the error signal where Td is a time rate constant . I t is important to remember that if the error is constant there is no corrective action with derivative control. 17 September 2019 Bioprocess Engineering 17

18. Response of a derivative controller to sinusoidal error inputs: This picture represent that the output is always in a direction to oppose changes in error, both away from and towards the set point , which in this example results in a 90° phase shift . 17 September 2019 Bioprocess Engineering 18

19. Combination of methods of control Three combinations of control systems are used : Proportional plus integral Proportional plus derivative Proportional plus integral plus derivative . 17 September 2019 Bioprocess Engineering 19

20. Proportional plus integral The output response to an error gives rise to a slightly higher initial deviation in the output signal compared with that which would be obtained with proportional control on its own . Proportional plus derivative The output response to an error will lead to reduces deviation, faster stabilization and a reduced offset compared with proportional control alone. 17 September 2019 Bioprocess Engineering 20

21. Proportional plus integral plus derivative This combination normally provides the best control possibilities . The maximum and settling point similar to those for a proportional derivative controller while the integral action ensures that there is no offset . C ontrollers The first primary automatic controllers were electronic control units : Adjusted manually Knowledge of control engineering is necessary to make correct adjustments . 17 September 2019 Bioprocess Engineering 21

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23. Reference : Principle of fermentation technology – P.F.Stanbury , A.Whitaker and S.J.Hall . 17 September 2019 Bioprocess Engineering 23

24. THANK YOU….. 17 September 2019 Bioprocess Engineering 24