Experiment Title:
Close loop control system
Subject:
UEEA3423 CONTROL SYSTEMS
Course:
MECHATRONICS ENGINEERING
Date of Experiment: 15 June 2017 Name of Lecturer:
Dr. Ng Oon-Ee
Name of Student YEOH BOON KHAI
Student ID No
Year and Semester
1403449
Y3S1
Received by: Dr. Ng Oon-Ee Lab Asst/ Lab Officer
Date:22/6/2017
Lab Asst/ Lab Officer Receipt of Lab Report Submission (To be keep by student)
Experiment Title:
Close loop control system
Subject:
UEEA3423 CONTROL SYSTEMS
Course:
MECHATRONICS ENGINEERING
Name of Student YEOH BOON KHAI
Received by: Dr. Ng Oon-Ee Lab Asst/ Lab Officer
Student ID No
Year and Semester
1403449
Y3S1
Date: 22/6/2017
Title: Close loop control system Objective: To study the relationship between the system gain and the result of the close loop control system. Background study
The goal of control system is to measure, monitor, and control a process .In order to achieve control in the accuracy way, it can be done by monitoring its output and “feeding” some of it back to compare the actual output with the desired output so as to reduce the error and if disturbed, bring the output of the system back to the original or desired response. The quantity of the output being measured is called the “feedback signal”, and the type of control system which uses feedback signals to both control and adjust itself is called a Close-loop System. Beside close loop system, open loop system also play an important role in the simple electronics application. Open loop system is a systems in which the output quantity has no effect upon the input to the control process are called open-loop control systems. Both of these system contain own advantages depend on the application apply. The below show the advantages of each type of system.
Open loop system Simple in construction and design Easy to maintain Convenient to use as output that is difficult to measure
Close loop system More accurate Facilitates automation System that less affected my noise
There are plenty of application in our daily created b y using the concept of close loop system. The table below show the daily application base on the close loop system concept. Application Water level controller Air conditional Automatic electric iron
Description Input water is controlled by water level in the reservoir Air conditional function depending on the temperature of the room Heating element controlled by output temperature of iron
Introduction Experiment Part A: Closed loop position controller
In a closed loop position controller system, the positional information from an output potentiometer (Po) which is mechanically coupled to a motor is fed back to a control amplifier. Then, the reference position input from the input potentiometer (Pi) is combined with the feedback signal at the input of the amplifier which drives the motor in proportion to the difference between two signals. When the two positions are identical, the output of the amplifier becomes zero. A simplified system diagram of a closed loop position controller which will be used in this experiment is shown in Figure 1.
There are three amplifiers in Figure 10-1. The A1 is an error signal generator, A2 is an error signal amplifier and A3 is the driver for the motor M. As Pi is turned away from Po, the difference between two potentiometers voltages become an error signal which appears at the input of A1. The error signal is further a mplified through A2 and A3, and drives the motor in the direction to reduce the error voltage between Pi and Po. Therefore, as Pi is turned clockwise, Po follows the same direction. This feedback action continues until the output of A1 is reduced to zero. At this point, the voltage measured at Pi and Po are same but in opposite polarity. For example, if Pi is at +3V, then Po is at -3V, making the sum of two zero. The final relative position between Pi and Po depends upon the gain of the amplifiers. For a large gain, the position of Po can be almost equal to the position of Pi. But when the gain is not sufficient, there can be an offset in the relative position. This offset is the “deadband” for a position controller.
Experiment Part B: Transient response of a position controller
When a step input is given to a position controller, the loop takes time to react to the applied input. Also, depending upon the given s ystem parameters, oscillation can occur at the output during the transient time period. The major cause of the time delay comes from the added inertia of the moving parts. Therefore, the higher the inertia, there will be more delay. Usually, the system gain is preferred to be high to improve system response time. However, when the gain becomes excessive, it will cause undesired overshoot at the output. Transient response of a system can be easily observed on an oscilloscope when the system is stimulated with a square wave input. Such an arrangement is shown in Figure 11-1.
The function generator in Figure 11-1 provides synchronized square-wave and ramp signals. As it is shown in the figure, the ramp signal is used to drive the Xinput of an oscilloscope. When the output voltage from Po is fed into the Yinput of the oscilloscope, transient response curves as shown in Figure 11-2 can be obtained. To get the best results, it is recommended that the frequency of the square-wave be kept below 1 Hz.
Methodology Diagram of setup Experiment Part A
Experiment Part B
Diagram of apparatus
Result Part A
1. Attenuation = 9
Clockwise
Anti-clockwise
Angle of U-157 / ° Anti-clockwise / Clockwise
Angle of U-158 / °
Offset error / °
Angle of U-158 / °
Offset error / °
0/360
350
10
10
10
10/350
340
10
22
12
20/340
340
0
22
2
30/330
340
10
22
8
40/320
335
15
32
8
50/310
323
13
42
8
60/300
315
15
54
6
70/290
303
13
62
8
80/280
295
15
75
5
90/270
285
15
82
8
100/260
270
10
95
5
110/250
265
15
102
8
120/240
250
10
112
8
130/230
245
15
122
8
140/220
235
15
132
8
150/210 Average offset error angle/ °
220
10
143
7
11.9375
7.4375
2. Attenuation = 7
Clockwise
Anti-clockwise
Angle of U-157 / ° Anti-clockwise / Clockwise
Angle of U-158 / °
Offset error / °
Angle of U-158 / °
Offset error / °
0/360
357
3
5
5
10/350
357
7
9
1
20/340
347
7
19
1
30/330
337
7
29
1
40/320
327
7
39
1
50/310
317
7
49
1
60/300
309
9
59
1
70/290
297
7
69
1
80/280
287
7
79
1
90/270
279
9
89
1
100/260
267
7
99
1
110/250
259
9
109
1
120/240
249
9
119
1
130/230
239
9
129
1
140/220
227
7
139
1
150/210 Average offset error angle/ °
219
9
145
5
7.5
1.5
3. Attenuation = 5
Clockwise
Anti-clockwise
Angle of U-157 / ° Anti-clockwise / Clockwise
Angle of U-158 / °
Offset error / °
Angle of U-158 / °
Offset error / °
0/360
355
5
10
10
10/350
352
2
11
1
20/340
345
5
20
0
30/330
334
4
29
1
40/320
325
5
42
2
50/310
314
4
51
1
60/300
306
6
59
1
70/290
297
7
72
2
80/280
287
7
82
2
90/270
275
5
91
1
100/260
267
7
101
1
110/250
257
7
110
0
120/240
247
7
120
0
130/230
237
7
130
0
140/220
222
2
140
0
150/210 Average offset error angle/ °
217
7
151
1
5.4375
1.4375
4. Attenuation = 3
Clockwise
Anti-clockwise
Angle of U-157 / ° Anti-clockwise / Clockwise
Angle of U-158 / °
Offset error / °
Angle of U-158 / °
Offset error / °
0/360
355
5
10
10
10/350
352
2
14
4
20/340
344
4
24
4
30/330
333
3
32
2
40/320
324
4
44
4
50/310
314
4
54
4
60/300
305
5
63
3
70/290
293
3
72
2
80/280
285
5
83
3
90/270
274
4
90
0
100/260
265
5
104
4
110/250
254
4
113
3
120/240
244
4
122
2
130/230
233
3
132
2
140/220
224
4
142
2
150/210 Average offset error angle/ °
216
6
154
4
4.0625
3.3125
5. Attenuation = 1
Clockwise
Anti-clockwise
Angle of U-157 / ° Anti-clockwise / Clockwise
Angle of U-158 / °
Offset error / °
Angle of U-158 / °
Offset error / °
0/360
355
5
9
9
10/350
352
2
14
4
20/340
343
3
23
3
30/330
333
3
35
5
40/320
324
4
43
3
50/310
314
4
53
3
60/300
304
4
63
3
70/290
293
3
73
3
80/280
284
4
83
3
90/270
275
5
93
3
100/260
264
4
103
3
110/250
253
3
113
3
120/240
244
4
123
3
130/230
234
4
133
3
140/220
223
3
143
3
150/210 Average offset error angle/ °
213
3
153
3
3.625
3.5625
Graph Experiment Part A
Deadband against attenuation 14 11.9375 12 10 d n a b d a e D
7.5
8
7.4375
5.4375
6
Clockwise
4.0625
3.625
Anticlockwise
4 1.5
1.4375
3.5625
2
3.3125
0 0
2
4
6
8
10
Attenuation
Deadband against System gain 14 11.9375 12 10 d n a b d a e D
7.5
7.4375
8
5.4375
6
Clockwise 4.0625
3.5625
4 1.5
2
1.4375
Anticlockwise
3.625
3.3125
0 0
2
4
6
System gain
8
10
Experiment Part B U152 = A U151 = 8
U151 = 6
U151 = 4
U151 = 2
U151 = 0
U152 = B U151 = 8
U151 = 6
U151 = 4
U151 = 2
U151 =0
Discussion
From the result base on experiment part A, it is clearly shown that the offset degree is decreasing when the system gain increase in both clockwise and anticlockwise case. When the attenuation is 1, the average of the offset angle in anticlockwise is closed to clockwise. Hence, the control system is stable when the system gain is bigger. The block diagram of experiment part A is shown in below. PO Pin
A1
A2
A3
M
Block diagram of experiment part A
Where A1=attenuator A2=pre-amplifier A3=motor driver amplifier M=motor and gearing
PO Pin
A1 A2 A3
M
Simplify Block diagram of experiment part A
Transfer function of experiment part A:
() =
2 3 1 + 2 3
=
In experiment part B, it is clearly observe that the system gain is increased, the response of the system improves. However, if the gain is too high, it will cause overshoot in the response. Furthermore, a capacitor is connected in parallel with a resistor in port B in order to increase the system gain and shorten the delay
time, As a result, a loop circle is formed in the control system when attenuation is 0.
Port A: a resistor in series Port B: a resistor and a capacitor in parallel
Conclusion In conclusion, the offset error angle is bigger with increasing the system gain in experiment part A. In experiment of part B, port A has only a r esistor in series whereas port B has a capacitor and a resistor in parallel. The use of capacitor is to increase the system gain. Hence, the transient response reached static state within the time given. However, the gain is even higher, it will form a loop in the transient response due to insufficient time given.
Reference
1. Pardon our interruption. (n.d.). Retrieved from http://www.electronicstutorials.ws/systems/closed -loop-system.html
