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Level & Flow Process Control

Chemical Engineering Lab Com Presentation
by

Yu Sheng Leong

on 22 November 2012

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Transcript of Level & Flow Process Control

Leong Yu Sheng
KEK100016 Examples: If
Intolerable offset--> + integral action(I).

Excessive oscillations-->+derivative action(D). Recommendation 1.Best Result,
Flow Control: P & I Control. (200, 0.07, 0)
Level Control: PID control. (20, 0.51, 0.21) Conclusion Always make sure there is enough water to be pumped to away damage to the pump.
Check leakage in device before starting experiment.
Power cables is in good condition to prevent electric shock. Precaution Device: Level and Flow Process Control Pilot Plant Model (SE102)
1.Set up the experiment. (Hand valves, main power & air compressor)
2.Set P I D values and set point using ‘Manual Mode’.
3.Change to ‘Auto Mode’ while increases set point and observe responses. Methodology Proportional control  offset occur.
PI control eliminates the offset. But low I lead to instability
PID control  Act faster & stabilize the system. The controller saturates when its output reaches a physical limit, either pmax or pmin.
Unable to eliminate steady state error. The controller output is proportional to the error signal.
p(t) – ps = Kc e(t)

p(t) : controller output, ps : bias value, Kc : controller gain or sensitivity e(t) : the error (set point–measured) Proportional Control (P only) tuning parameters that are used to improve the response on the system.
P: Proportional Control
I: Intergral Action
D: Derivative Action P I D Control that utilizes multiple feedback loops.

It use a secondary measurement point and a secondary feedback controller to decrease upsets in a system.

The performance is better for all type of load changes. Cascade control Flow Control It has fast responses on order of seconds. Flow control The value of variable being controlled is manipulating according to the ‘error’ for corrective adjustment. Feedback Control is a process to keep conditions such as flows, temperatures, levels and pressures within certain limits. Process control defined as the action to maintain desired conditions in a physical system by adjusting selected variables in the system. Control To obtain the best combination of the P,I & D onto the flow system, level system and cascade system. Objective Level & Flow Process Control It anticipate the future behavior of the error signal by considering its rate of change.

The controller output proportional to the rate of change of the controlled variable. Derivative control action

Reset wind-up :
create oscillatory responses of the controller process
reducing the stability of the system. Integral control action The proportional band is defined as,


PB is defined as the range of level over which the control valve will go from fully closed to fully open. (as 0 to 100%) Proportional Control (P only) The feed to the system is fixed and the level is controlled by adjusting the exit flow

to maintain a constant level of liquid.
Level Control I=0.02 I=0.07 I=0.11 Choosing the Best Result Cascade Loop Single Loop Load changes Response Observe the response of the controller when the disturbance encountered to study the action of PID controller. The system depends mainly on the size of the lags in the measuring device, the controller, the transmission line, and the control valves. Most of the disturbances are high-frequency noise. D could not be applied for fast and noisy process (such as flow). Cascade control is better than single loop. Trial & error should be carried out for cascade loop to find the best combination.
The selection among the control systems depends on the particular application. Thank You Q & A... Be happy. It's one way of being wise. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
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