Electrical and Instrumentation Engineering Practical Assignment

This document provides a detailed solution to a practical assignment for the Advanced Diploma of Electrical and Instrumentation (E&I) Engineering program, focusing on oil and gas facilities. The assignment covers various aspects of process control using PC-ControLAB, including determining the range and value of the process variable (PV), analyzing the behavior of the PV in manual mode, and calculating the gain of the process. The solution also addresses controller tuning using P, PI, and PID parameters, exploring the relationship between the set point and PV, and explaining the impact of measurement noise on the output. The assignment delves into troubleshooting scenarios, such as stabilizing a temperature loop, and provides references to relevant control theory and PID control principles.

SOLUTIONS TO THE QUESTIONS
Question 1
Start PC-ControLAB
Press PROCESS
Press SELECT MODEL
In front of you (middle right), select FLOW.MDL, and open this
1.1 What is the range of the PV in GPM? (1)
0 – 50 GPM for current process variable
1.2 What is the approximate value of the PV in GPM? (1)
25.5 GPM
1.3 Why is the PV acting the way it does (moving up and down slightly as the controller is in
MANUAL)?
Most controllers are integrated such that all the three fundamental control parameters, that is: P, I and
D-controller parameters are harmoniously combined to bring about a smooth functional output. In the
manual mode, this feature is lost hence due to systemic and external interferences (noise), the PV
profile will be dominated by overshoots and undershoots. Tuning will require error correction that
involves establishing the difference between the targeted value and the actual value and this must be
minimized in the process (Didactic, 2014).
(2)
Press VIEW (near the top)

Advanced Diploma of Electrical and Instrumentation (E&I) Engineering for Oil and Gas Facilities (DEI) 2
Select HORIZONTAL GRID SCALE, and select SECONDS
Still under VIEW (near the top), select DISPLAY RANGE and select PERCENT OF SPAN
Click on PROCESS (near the top) and then click on CHANGE PARAMETERS
In the middle, under item 26, you will see something that says “Valve Po: 0=no; 1=Yes”. Click on
this, and it will ask you for a NEW VALUE. (The present value will be 0). Just type in a value of 1.
At the bottom, click on OUT, and take the OUTPUT to 35%
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Advanced Diploma of Electrical and Instrumentation (E&I) Engineering for Oil and Gas Facilities (DEI) 3
Jot down the approximate PV
(15%)
At the bottom, click on OUT, and take the OUTPUT to 60%
Jot down the approximate PV
(38%)
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Advanced Diploma of Electrical and Instrumentation (E&I) Engineering for Oil and Gas Facilities (DEI) 4
1.4 Calculate the Gain of the Process (4)
You must provide all calculations, marks will be deducted.
HINT : Gain of the process = change of PV / change of controller output
We obtain the values from the PV and output graphs above: hence PV1= 0.255, PV2= 0.38 and OP1=
40, OP2= 60 hence substituting in the equation below:
Kp= ∆ PV
∆ Output = (0.38-0.255)/(60-40)
= 0.125/20
= 0.00625
Click on TUNE, and put in a value of 0.8, under GAIN, and press OK, followed by CLEAR
Press AUTO (bottom right).
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Advanced Diploma of Electrical and Instrumentation (E&I) Engineering for Oil and Gas Facilities (DEI) 5
Press SP (bottom left), and type in a value of 40 (for 40%).
1.5 What is the value of the PV? (1)
(15%)
1.6 Why does it not go to the Set Point? (2)
Since it is in manual mode where operator does the tuning by herself. Bringing it to proper control may
necessarily not be 100% attainable. There are always safe limits between which controller stabilizes
the system hence the discrepancy (Control Theory, no year).
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Advanced Diploma of Electrical and Instrumentation (E&I) Engineering for Oil and Gas Facilities (DEI) 6
Click on TUNE, and put in a value of 0.1, under RESET, and press OK, followed by CLEAR
1.7 What is the relationship between Set Point and the PV? (2)
The two values are used in error correction. In filtering the noise, the difference between the two must
be minimized.
Click on TUNE, and put in a value of 0.01, under DERIV, and press OK, followed by CLEAR
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Advanced Diploma of Electrical and Instrumentation (E&I) Engineering for Oil and Gas Facilities (DEI) 7
1.8 What do you notice about the blue pen (Output). (2)
Blue pen mark became volatile and distorted
Click on PROCESS (near the top) and then click on CHANGE PARAMETERS
In the middle, under item 40, you will see something that says “Meas. Noise: 0 = Off; 1=On”. Click
on this, and it will ask you for a NEW VALUE. (The present value will be 1). Just type in a value of
0.
1.9 What does the blue pen do, now? Explain this phenomenon. (2+1=3)
Blue pen out line returned to steady output without distortion approx. 56%
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Advanced Diploma of Electrical and Instrumentation (E&I) Engineering for Oil and Gas Facilities (DEI) 8
1.10 You are using PI control on a temperature loop, and it just does not want to stabilise. Any
ideas what you might want to set / adjust, in order to stabilize the loop, and get the PV to stop
oscillating, and settle down at the Set Point? (2)
The trial and error method can be used for this case. It will require tuning of the P, PI, and PID
parameters as described below.
The P-action implantation:
Firstly, the manual mode will have to be switched off. Meanwhile, the integral and
derivative actions are to be in passive off-mode. The controller gain is then set to a small
value say 1. With the controller on automatic, make a step change and observe the
process variable. Although the stabilization process will take slightly longer to take effect.
The PV behaviour has to exhibit an underdamped response (Haugen et al, 2007). If still
oscillating, improve the Kc by a factor of say 2.5 and observe again. This is to be
repeated until the oscillatory behaviour is replaced by an underdamped condition. At this
point, the system will settle 63% and therefore stabilizes.
As for the integral action, the Ki factor is to be decreased until the above mentioned resulting
condition is attained.
Lastly, the derivative portion is tuned by first ensuring the derivative Td is fixed at the
smallest value. This should be done by a factor of 2. This is to be done without unnecessarily
high number of overshoots. In fact, as it gets better, the overshoots are eliminated as well.
References
Didactic, F. (2014). Process Control Pressure, Flow, and Level. Quebec.
Control Theory. No year. Lab 2, Analysis and Design of PID Controllers. Available at:
https://www.kth.se/social/upload/53071bc3f276543dbb5fa984/lab2.pdf
Haugen,F , Fjelddalen,E , Dunia,R , & Thomas, F. (2007). Demonstrating PID Control
Principles using an Air Heater and LabVIEW. Available at:
http://home.hit.no/~finnh/cv/docs/finn_haugen_cache_2007.pdf
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