MEASUREMENTS and CONTROL LAB. 0908448

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MEASUREMENTS and CONTROL LAB.
0908448

• CONTROL EXPERIMENTS

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List of Experiments

• DC Servo Motor Control.
• Twin Rotor Control.
• Pneumatic and Electro-Pneumatic System Control.
• Programmable logic Controllers PLCs.
• System Identification.

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OBJECTIVES

• The aim of this experiment is to provide students
  with a sound introduction to the principles of
  analogue servomechanisms, and by extension to
  those of closed-loop systems more generally.

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EQUIPMENT and APPARATUS

• Power supply
• Feedback, 33-002 Servo Fundamentals Trainer,
  which consists of the following
• Mechanical Unit 33-100
• Analogue Unit 33-110
• Digital unit the 33-120
• Software pack 33-911
• Personal computer

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Mechanical Unit 33-100
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Analogue Unit 33-110
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The Closed Control Loop
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Block Diagram of an Analogue Closed-Loop System
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Block Diagram of a Digital Closed-Loop System
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Representation of a Motor in terms of an Ideal
Motor
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Characteristic of Magnetic Brake
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PART I Steady-State Characteristics
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Since the reduction to the output shaft is 321,
the motor speed is calculated by multiplying the
r/min reading by 32 eg, a reading of 31.25 a
motor speed of 1000 r/min.
Amplifier Input (Volts) Output Shaft Speed (RPM) Motor Speed (RPM)
10
9
7.5
5
2.5
1
0
-1
-2.5
-5
-7.5
-9
-10
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Brake Load
Brake Setting Armature current Ia (Amps) Output Shaft Speed (RPM) Motor Speed (RPM)
0
1
2
3
4
5
6
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PART II Error Channel and Feedback Polarity
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Step Response

• friction force (stiction)

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P1 percentage value () Ta (Settling Time) (s) Peak Vo Value (Volts) Overshoot Value (Volts) Overshoot Percentage () System behavior
0
10
20
30
50
70
80
100
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PART IV Velocity Feedback
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PART V Speed Control System
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Brake Setting Armature current Ia (Amps) Output Shaft Speed (RPM) Motor Speed (RPM)
0
1
2
3
4
5
6
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Digital unit 33-120
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Analogue to Digital Converters

• If signals in the form of continuous waveforms
  (analogue) are required to be processed in a
  computer, the signals must be converted into a
  digital (binary) form.
• if a typical 8-bit A/D converter is used, then
  28256 levels are present in the output and with
  a 10-bit one, the output is represented by
  2101024 levels. So you can see that the greater
  the number of bits, the higher the output
  resolution, but the more complex and costly is
  the converter.

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Pulse Width Modulation

• dc motors are often used because the speed and
  direction are controlled by the magnitude and
  direction of the applied voltage. Since the
  signal intended to operate the motor is a low
  power signal, a power amplifier is required to
  drive the motor.
• The signal applied to the motor is a square wave,
  the mark/space ratio of which is varied while the
  frequency is kept constant. This drive method is
  called Pulse Width Modulation (PWM).

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Digital Shaft Position Sensing

• Absolute Encoder
• Incremental Encoders

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THE END