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FACULTY OF ENGINEERING

DEPARTMENT OF CHEMICAL AND ENVIRONMENTALENGINEERING

 ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ 

ECH 3112

PROCESS CONTROL & INSTRUMENTATIONLABORATORY

Submitted to:DR. SYAFIE - LECTURER

Prepared by: (GROUP 6)

SIOW ZHI HOONG (

HO CHAI LING (

SAIFUL BAHRI BIN ABD AZIZ (140515)

Experiment Date: 20th AUGUST 2009

Date Submitted: 3rd SEPT 2009

1.0 INTRODUCTION

MODUL 2

FLOW CONTROL

(SHORT REPORT)

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A proportional–integral–derivative controller (PID controller) is a

generic control loop  feedback mechanism (controller) widely used in

industrial control systems. A PID controller attempts to correct the error

between a measured process variable and a desired set point by calculating

and then outputting a corrective action that can adjust the process

accordingly and rapidly, to keep the error minimal.

  The PID controller calculation (algorithm) involves three separate

parameters; the proportional, the integral and derivative values. The

proportional value determines the reaction to the current error, the integral

value determines the reaction based on the sum of recent errors, and the

derivative value determines the reaction based on the rate at which the errorhas been changing. The weighted sum of these three actions is used to

adjust the process via a control element such as the position of a control

valve or the power supply of a heating element.

By tuning the three constants in the PID controller algorithm, the

controller can provide control action designed for specific process

requirements. The response of the controller can be described in terms of 

the responsiveness of the controller to an error, the degree to which the

controller overshoots the set point and the degree of system oscillation. Note

that the use of the PID algorithm for control does not guarantee optimal 

control of the system or system stability.

Some applications may require using only one or two modes to provide

the appropriate system control. This is achieved by setting the gain of 

undesired control outputs to zero. A PID controller will be called a PI, PD, P or

I controller in the absence of the respective control actions. PI controllers are

particularly common, since derivative action is very sensitive to

measurement noise, and the absence of an integral value may prevent the

system from reaching its target value due to the control action.

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2.0 RESULT AND DISCUSSION

a. raw experimental data

FIC11 & FIC12PB2 : 150%

  TI2 : 6 seconds  TD2 : 0 secondsSV2 at FIC11 : 5m3/hrSV2 at FIC12 : 4.5 m3/hr

FIC11 & FIC12

PB2 : 150%  TI2 : 6 seconds  TD2 : 0 secondsSV2 at FIC11 : 3m3/hrSV2 at FIC12 : 2.5 m3/hr

FIC11 & FIC12PB2 : 100%

  TI2 : 6 seconds  TD2 : 0 seconds

SV2 at FIC11 : 5m3

/hrSV2 at FIC12 : 4.5 m3/hr

No.4FIC11 & FIC12PB2 : 100%

  TI2 : 6 seconds  TD2 : 0 secondsSV2 at FIC11 : 3m3/hr

SV2 at FIC12 : 2.5 m

3

/hr

No.5 (apply disturbance)SV2 at FIC11 : 5m3/hrSV2 at FIC12 : 4.5 m3/hr

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FIC12 left alone at,

PB2 : 150%  TI2 : 6 seconds  TD2 : 0 secondsSV2 : 2.5 m3/hr

FIC11PB2 : 150%

  TI2 : 6 seconds  TD2 : 0 secondsSV2 : 3 m3/hr,

(6a)= 3.5 m3/hr,

(6b)= open manual by-pass valve for 5 min.(6c)= increased MV by10%

(Test disturbance)No.7PB2 : 100%

No.8PB2 : 200%

PB2 : 150%  TI2 : 9 seconds  TD2 : 0 seconds

PB2 : 2%

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PB2 : 20%

PB2 : 40%

PB2 : 60%

 Table: raw experimental data.

 To study the responses from different PID settings in the flow control,

two systems have been used. The inflow system is using LIC/FIC11 and the

outflow system is using TIC11/FIC12. First at all, the tank T12 is filled with

water till it reaches the overflow Drain pipe outlet (D).

 The experiment results were shown in the graph of figure 1. When the

experiment started, four difference color lines were shown on the paper by

the chart recorder. First, the red color line indicates the water level in the

tank T12, green color line indicates inflow, blue color line indicates the

outflow and the purple color line indicates the temperature. By referring the

purple color line in the graph printed by the chart recorder, the line is linear;

therefore the temperature in the system remains constant through the whole

process.

 The Proportional (P) and Integral (I) control is set into FIC11 and FIC12

by using the trial PID values for both controllers, that is PB2= 150%, TI2= 6s

and TD2= 0s. (PI action controller.) The first disturbance is observed when

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the inflow set point was 5m3/hr which is specified at point 1.The disturbance

that presence can be detected by moderate oscillation and the damping

pattern of green line.

Meanwhile, when the outlet flow rate which was changed to 4.5m3/hr,

the blue line was increased steadily to its steady state in a monotonic

pattern, which was no any oscillation. This is shown at point 2. As a result,

the respond of inflow was a sinusoidal response whereas outflow was a first

order step response. Both inflow and outflow increased gradually which then

led to the rise of water level in tank T12. The red line moved upward as

shown in the graph indicates that the water level in T12 is rise due to the

increased of water inflow. Gradually, the response would reach a new steadypoint. However, it would be take some time to reach the new steady point.

When the inflow and outflow are nearly steady with slight oscillations

about the set points, the inflow and outflow were set to 3.0m3/hr and

2.5m3/hr respectively (point 3) in the auto mode. This disturbance caused

the inflow and outflow decreased to the values of the new set points in a

negative step change response. This is because the controller had detected

that the values of the controlled/process variables are much higher than thenew set points.

As a result, the response of inflow was decreased in an over damp

oscillation pattern whereas outflow decreased again in a monotonic pattern

in order to reach its steady state.

As the system was achieved steady state, the PID control was change

value of PB2 from 150% to 100% with the inflow and the outflow were

increased to 5.0m3/hr and 4.5m3/hr respectively (indicated point 4). There

was an increment due to the increased of flow with the outflow shown a

slower response. When the inflow and the outflow were adjusted to 3.0m3/hr

and 2.5m3/hr, the chart showed a decrement pattern with an over damp

oscillation.

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 The pattern of the curve of PB2 = 100% is almost similar to the pattern

of the curve of PB2 = 150%. This verify that PB = 150% has no significant

difference with PB = 100%. This slight difference is due to the slightly

difference in K c.

At this section of recording, the level in the tank increased to its

maximum value and became stable at this value. Changes in the inflow and

outflow did not affect the level because the inflow is still larger than the

outflow. From point 1 to point 4, the temperature is remain constant without

any changes and the water level is also remain constant at the maximum

value as the inflow is always set to be larger than outflow to avoid the tank

to drain out.

When the inflow and outflow were increased to 5.0m3/hr and 4.5m3/hr

respectively (indicated point 5), the green and blue lines increased to new

set points but the outflow line shown a slower response. After a period of 

time the inflow will approach the new set point. When the inflow and outflowwere reduce to 3.0m3/hr and 2.5m3/hr, the lines decreased until it stabled

and reached the new set point. The level in the tank increased to its

maximum value and became stable at this value.

After the system achieved steady state, the outflow was set at

2.5m3/hr, PB2 = 150%, TI2 = 6 seconds and TD2 = 0 seconds. Therefore, the

blue line remained at a constant value. At point 6(a), the inflow was

increased to 3.5m3/hr and decreased to 3.0m3/hr. The result indicated that

the changes were due to a step input since the graph didn’t show an

oscillation pattern.

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Next, the by-pass valve was opened for 5 seconds (indicated point

6(b)), the inflow was increased in a sudden and dropped drastically when the

valve was closed.

Also, the response for the water level decreased severely due to the

shutting of valve and gradually increased after a while. At point 6(c), the MV

was step increased by 10% manually and the result showed the inflow

increased and formed a small overshoot.

When the three steps 1(a), 1(b) and 1(c) are repeated with different

values of PB2 = 100% and 200% in the disturbance test for the inflow

loop(indicated point 7 & 8), we observed The chart recorder shows the same

pattern of responses with small oscillation and no significant oscillation

amplitude difference for both PB2 values.

 Theoretically, a larger PB will give a smaller steady gain due to their

inverse proportional relationship and hence they are in reciprocal. A smaller

steady gain will give damper oscillation in process controlling. However, the

chart shows no obvious difference in the oscillation amplitude because theflow rate that we use is too small due to machine error.

Once the system became stable, the PB2 was set back to 150% and

 TD2 at 0 second but the T12 was set at 9 seconds. The same results were

observed instead of the third step (indicated point 9). The system could not

go back to the previous steady set point at 3.0m3/hr when MV is increased by

10%. Instead, an offset is observed. Proportional controller cannot eliminate

the error completely, but there will be an offset between the output and the

set point. In this case, the derivative does not take place, since TD2 = 0.

 Therefore the offset persists.

 The step from point 10 to 13 was done to determine the K c of the

controller. From point 10 up to 13, the PB2 was increased from 2%, 20%,

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40% and 60%. TI2 was adjusted to 6 seconds once again. The TD2 was

remained at 0 seconds. The value of K c increased drastically. These values

were too large and over the stability limit. Large dampen oscillations were

observed because of larger K c will increase instability and cause larger

oscillation.

When a disturbance is applied to the set point, the flow rate changed

drastically. But when PB2 was set higher and higher until 60%, the oscillation

was become smaller (indicated point 13).

 Thus, the critical value for PB2 is around 60%. Here, the value of K c is

the limiting proportionality of the proportional controller. Any K c value over

this limiting value will results an unstable response. The time to reach steady

state will also increase as K c increase.

Finally, we re-adjusted the PB2 value to 150% (indicated point 14), TI2at 6 seconds and TD2 at 0 second. This setting brought the system to PID

system. Vigorous oscillation was obtained as the inflow was disturbed by

opening/closing the by-pass valve of pump P12. The derivative action gives

the controller the capability to anticipate where the process is heading. The

amount of anticipation is decided by the value of TD. Right now, this

controller not only can integrate the error, but also calculate the rate of 

error. Thus, it is a more efficient controller. The oscillation dampened a little

when the test at point 6 was applied but became stabilize in a quick time. In

reality, time should be given more to observe the reduction of the oscillation.

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3.0 CONCLUSION AND RECOMMENDATIONS

From the experiment, we can prove that Proportional Integral

Derivative Controller (PID) is a useful controller as it can deal with different

disturbances. The derivative action gives the controller the capability to

anticipate where the process is heading by calculating the error.

Different disturbances test are done purposely in order to observe PID

controller to eliminate the error. The PID controller will only take the control

action in the auto mode. That is why this controller is more efficient than

others. However, there still have some disadvantages of this controller such

as not suitable for the fast and noisy system like the flow system. Fast

process is easily susceptible to process noise. Typical of this fast process are

flow loop such as what we did in this experiment. The application of the

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