1. MISS. RAHIMAH BINTI OTHMAN
ERT 422/4
Control system instrumentation
MISS. RAHIMAH BINTI OTHMAN (

2. OUTLINES
Basic concepts of process dynamics and process control in bioprocess plant system.
The needs of control system.
Types of controller required in the selected plant processes
A case study.

3. TYPES OF CONTROLLER IN PROCESS PLANT

4. CONTROL TERMINOLOGY 1. Controlled Variables (CV)
3. Disturbance Variables (DV)
2. Manipulated Variables (MV)
CONTROL TERMINOLOGY
4. Setpoint
7. Controller
6. Final Control Element
5. Sensor

5. CONTROL TERMINOLOGY
Controlled Variables (CV) - these are the variables which quantify the performance or quality of the final product, which are also called output variables (Set point).
Manipulated Variables (MV) - these input variables are adjusted dynamically to keep the controlled variables at their set-points.
Disturbance Variables (DV) - these are also called "load" variables and represent input variables that can cause the controlled variables to deviate from their respective set points (Cannot be manipulated).
Setpoint – the desired o specified value for the CV.
Sensor – the device that measures a process variable.
Final Control Element – the system that changes the level of the MV. The final control element usually involves a control valve and associated equipment or a variable speed pump.
Controller – a unit which adjusts the MV level to keep the CV at or near its setpoint.

6. TYPE OF PROCESS CONTROL LOOP Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Cascade Control
Ratio Control
Split Range Control
Differential Control
DESIRED OUTPUT

7. BACKGROUND
Normally a chemical or biochemical process has numerous inputs
and many outputs.
Consider the diagram below:
The objective of a control system is to keep the cv’s at their desired values (or setpoints). This is achieved by manipulating the mv’s using a control algorithm.

8. TYPE OF PROCESS CONTROL LOOP Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Cascade Control
Ratio Control
Split Range Control
Differential Control
DESIRED OUTPUT

9. FEEDBACK CONTROL 2. Applications 3. Positive Feedback 1. Objectives
4. Negative Feedback
8. Advantages & Disadvantages
5. Process Variables
(CV, MV, DV, SP)
6. Possible Block Diagram
7. Control System Diagram

10. FEEDBACK CONTROL SYSTEM; (Example: Blending System)
* Notation:
w1, w2 and w are mass flow rates
x1, x2 and x are mass fractions of component A
Block Diagram For The Feedback Control System

11. Assumptions:
w1 is constant
x2 = constant = 1 (stream 2 is pure A)
Perfect mixing in the tank
Control Objective:
Keep x at a desired value (or “set point”) xsp, despite variations in x1(t). Flow rate w2 can be adjusted for this purpose. Method 1. Measure x and adjust w2.
Terminology:
Controlled variable (or “output variable”): x
Manipulated variable (or “input variable”): w2
Disturbance variable (or “load variable”): x1

12. FEEDBACK CONTROL SYSTEM; (Example: Blending System)

13. TYPE OF PROCESS CONTROL LOOP Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Cascade Control
Ratio Control
Split Range Control
Differential Control
DESIRED OUTPUT

14. FEEDFORWARD CONTROL 1. Objectives 2. Applications 5. Process Variables
(CV, MV, DV, SP)
FEEDFORWARD
CONTROL
8. Advantages & Disadvantages
6. Possible Block Diagram
7. Control System Diagram

15. Method 2. Measure x1 and adjust w2.
Measure disturbance variable x1 and adjust w2 accordingly
Thus, if x1 is greater than , we would decrease w2 so that
If x1 is smaller than , we would increase w2.

16. TYPE OF PROCESS CONTROL LOOP Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Cascade Control
Ratio Control
Split Range Control
Differential Control
DESIRED OUTPUT

17. FEEDFORWARD-PLUS-FEEDBACK CONTROL
Because of the difficulty of accounting for every possible load disturbance in a feedforward system, this system are often combined with feedback systems.
Controller with summing functions are used in these combined systems to total the input from both the feedforward loop and the feedback loop, and send a unified signal to the final control element.  FC TC
Process variable need to be controlled = Temperature FT
Fluid in TT Y
Steam
Fluid out
LCV-100

18. TYPE OF PROCESS CONTROL LOOP Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Cascade Control
Ratio Control
Split Range Control
Differential Control
DESIRED OUTPUT

19. CASCADE CONTROL; EXAMPLE
The normal block diagram representation of a cascade control
loop is shown below,

20. CASCADE CONTROL Cascade Control
Cascade Control uses the output of the primary controller to manipulate the set point of the secondary controller as if it were the final control element.
Reasons for cascade control:
Allow faster secondary controller to handle disturbances in the secondary loop.
Allow secondary controller to handle non-linear valve and other final control element problems.
Allow operator to directly control secondary loop during certain modes of operation (such as startup).

21. TYPE OF PROCESS CONTROL LOOP Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Cascade Control
Ratio Control
Split Range Control
Differential Control
DESIRED OUTPUT

22. PIPING AND INSTRUMENTATION DIAGRAM (P&ID)
Ratio Control (cont…)
Application: - Blending two or more flows to produce a mixture with
specified composition.
- Blending two or more flows to produce a mixture with
specified physical properties.
- Maintaining correct air and fuel mixture to combustion.
FIC FF FT FT
Water
Acid
2 part of water
1 part of acid

23. TYPE OF PROCESS CONTROL LOOP Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Cascade Control
Ratio Control
Split Range Control
Differential Control
DESIRED OUTPUT

24. PIPING AND INSTRUMENTATION DIAGRAM (P&ID)
Split Range Control FC FT
Valve A
Valve B

25. TYPE OF PROCESS CONTROL LOOP Feedforward-plus-Feedback Control
Feedforward Control
Feedforward-plus-Feedback Control
Cascade Control
Ratio Control
Split Range Control
Differential Control
DESIRED OUTPUT

26. PIPING AND INSTRUMENTATION DIAGRAM (P&ID)
Differential Control
Meaning
Systems Theory:
In differential control, control action is based on the change (derivative) of the control error. The control error is defined as the difference between the set point and the process output.
Explanation:
Derivative control is used to provide anticipative action. This is done by using the current change (derivative) of the control error to estimate the error some time ahead and act anticipatively on this estimation.