1. FINAL CONTROL ELEMENT

2. The final control element adjust the amount of energy/mass goes into or out from process as commanded by the controller The common energy source of final control elements are: –Electric –Pneumatic –Hydraulic

3. ELECTRIC FINAL CONTROL ELEMENT Electric current/voltage Solenoid Stepping Motor DC Motor AC Motor

4. CHANGING CURRENT/VOLTAGE Current or voltage can be easily changed to adjust the flow of energy goes into the process e.g. in heating process or in speed control Heater elements are often used as device to keep the temperature above the ambient temperature. Energy supplied by the heater element is W = i 2 rt (i=current, r=resistance, t=time) Motor is often used as device to control the speed

5. CHANGING CURRENT/VOLTAGE Using – Potentiometer –Amplifier –Ward Leonard system –Switch (on-off action)

6. Changing Current/Voltage Using Rheostat Rheostat Heater R1R1 R2R2 I = V/(R 1 +R 2 ) Power at rheostat P 1 =I 2 R 1 Power at heater P 2 =I 2 R 2 Disadvantage loss of power at rheostat V I

7. Example of Heating elements

8. Changing Current/Voltage Using Amplifier V Potentiometer R1R1 R2R2 amplifier V+V+ V−V− Heater Disadvantage loss of power at potentiometer (very small) and at Amplifier

9. Changing Current/Voltage Using Ward Leonard System Introduced by Harry Ward Leonard in 1891 Use a motor to rotate a generator at constant speed The output of generator voltage is adjusted by changing the excitation voltage Small change in excitation voltage cause large change in generator voltage Able to produce wide range of voltage (0 to 3000V) Ward Leonard system is popular system to control the speed of big DC motor until 1980’s Now a days semi conductors switches replaces this system

10. Changing Current/Voltage Using Ward Leonard System MOTORGENERATOR excitation voltage

11. Changing Current/Voltage Using Switch The switch is closed and opened repeatedly No power loss at switch V LOAD Switch t VLVL VLVL V Switch closed Switch opened

12. DUTY CYCLE T is period time typical in millisecond order (fix) T on is switch on time (adjustable) T off is switch off time Duty Cycle is: (T on /T) 100% t VLVL V T on T off T Of course we can not use mechanical switches to carry on this task, electronic switches to be used instead. E.g. Transistor, Thyristor, or IGBT This methods is often called as Pulse Width Modulation (PWM)

13. SOLENOID When the coil is energized the core will be pulled in SOLENOID core coil core

14. SOLENOID When the coil is energized the core will be pulled in V SIMULATE

15. SOLENOID When the coil is energized the core will be pulled in V SIMULATE

16. SOLENOID Tubular solenoidOpen frame solenoid Rotary solenoid

17. Solenoid

18. Solenoid Usage pushing buttons, hitting keys on a piano, Open closed Valve, Heavy duty contactor jumping robots etc

19. STEPPING MOTOR The top electromagnet (1) is turned on, attracting the nearest teeth of a gear-shaped iron rotor. With the teeth aligned to electromagnet 1, they will be slightly offset from electromagnet The top electromagnet (1) is turned off, and the right electromagnet (2) is energized, pulling the nearest teeth slightly to the right. This results in a rotation of 3.6° in this example.

20. STEPPING MOTOR The bottom electromagnet (3) is energized; another 3.6° rotation occurs. The left electromagnet (4) is enabled, rotating again by 3.6°. When the top electromagnet (1) is again enabled, the teeth in the sprocket will have rotated by one tooth position; since there are 25 teeth, it will take 100 steps to make a full rotation in this example.

21. STEPPING MOTOR Practical stepping motor can be controlled for full step and half step. Common typical step size is 1.8 o for full step and 0.9 0 for half step Full step is accomplished by energizing 2 adjacent electromagnet simultaneously. Half step is accomplished by energizing 1 electromagnet at a time.

22. Stepping motor

23. DC Motors Every DC motor has six basic parts – axle, rotor (a.k.a., armature), stator, commutator, field magnet(s), and brushes. For a small motor the magnets is made from permanent magnet

24. 2 pole motor Animate

25. 3 pole DC motors + − The coil for each poles are connected serially. The commutator consist of 3 sector, consequently one coil will be fully energized and the others will be partially energized. 1 3 2

26. DC motors As the rotor is rotating, back emf (E a ) will be produced, the faster the rotor turn the higher E a and the smaller I a. The starting current of motors will be much higher then the rating current. motor V EaEa IaIa

27. DC motors For big motors the magnet is made from coil and core. The current flowing in the coil is called I f and the current flowing in the armature is called I a. The armature winding and the field winding are connected to a common power supply The armature winding and the field winding are often connected in series, parallel, or compound. The torque characteristic will be different for each connection. The figure shows a parallel connection Field winding Armature winding

28. SERIES DC MOTOR Field and armature winding are series connected, this type of motor is called series DC motor

29. DC motors Field and armature winding are parallel connected, this type of motor is called shunt DC motor

30. DC MOTOR Compound DC motor is DC motor having 2 field winding the first one is connected parallel to the armature winding and the other is connected series

31. DC MOTOR Torque: T = KΦIa –K is a constant –Φ magnetic flux –I a is armature current Magnetic flux is constant if it is from permanent magnet It is depend on the I f if it is produced by current

32. DC MOTOR TORQUE-SPEED CURVE Torque: T = KΦIa

33. SERIES DC MOTOR TORQUE- SPEED CURVE Torque: T = KΦIa T= KI a 2

34. SHUNT DC MOTOR TORQUE- SPEED CURVE Torque: T = KΦIa

35. COMPOUND DC MOTOR TORQUE-SPEED CURVE

36. SYNCHRONOUS AC MOTOR NSNS ~ The rotating field. When alternating current is applied to the field coil the magnetic field will also alternating. Therefore the permanent magnet will rotate o 311 -311

37. THREE PHASE SYNCHRONOUS AC MOTOR 4 pole 3 Φ motor T S R R S T R S T NSNS

38. SYNCHRONOUS AC MOTOR

39. SYNCHRONOUS AC MOTOR USING EXTERNAL EXITER R S T The magnetic flux of permanent magnet is low for a bigger motor we have to use externally exited magnetic field

40. ASYNCHRONOUS AC MOTOR I induced When instead of exited, the rotor coil is shorted an induced current will be generated and the rotor will be magnetized and start to turn. The faster the speed the smaller the induced current and finally the current will cease at synchronous speed and so does the rotation This motor will turn at speed less the its synchronous rotation that is why it called asynchronous motor This motor is also called induction motor

41. Calculating Motor Speed A squirrel cage induction motor is a constant speed device. It cannot operate for any length of time at speeds below those shown on the nameplate without danger of burning out. To Calculate the speed of a induction motor, apply this formula: Srpm = 120 x F P Srpm = synchronous revolutions per minute. 120 = constant F = supply frequency (in cycles/sec) P = number of motor winding poles Example: What is the synchronous of a motor having 4 poles connected to a 60 hz power supply? Srpm = 120 x F P Srpm = 120 x 60 4 Srpm = 7200 4 Srpm = 1800 rpm

42. Calculating Braking Torque Full-load motor torque is calculated to determine the required braking torque of a motor. To Determine braking torque of a motor, apply this formula: T = 5252 x HP rpm T = full-load motor torque (in lb-ft) 5252 = constant (33,000 divided by 3.14 x 2 = 5252) HP = motor horsepower rpm = speed of motor shaft Example: What is the braking torque of a 60 HP, 240V motor rotating at 1725 rpm? T = 5252 x HP rpm T = 5252 x 60 1725 T = 315,120 1725 T = 182.7 lb-ft

43. Calculating Work Work is applying a force over a distance. Force is any cause that changes the position, motion, direction, or shape of an object. Work is done when a force overcomes a resistance. Resistance is any force that tends to hinder the movement of an object.If an applied force does not cause motion the no work is produced. To calculate the amount of work produced, apply this formula: W = F x D W = work (in lb-ft) F = force (in lb) D = distance (in ft) Example: How much work is required to carry a 25 lb bag of groceries vertically from street level to the 4th floor of a building 30' above street level? W = F x D W = 25 x 30 W = 750 -lb

44. Pneumatic Actuator

45. Reverse-Acting Actuator

47. I/P Converter A "current to pressure" converter (I/P) converts an analog signal (4-20 mA) to a proportional linear pneumatic output (3- 15 psig). Its purpose is to translate the analog output from a control system into a precise, repeatable pressure value to control pneumatic actuators/operators, pneumatic valves, dampers, vanes, etc. I/P Air supply 30 psi Current 4 to 20 mA Pneumatic 3 to 15 psi Supplied to actuator

48. Sample of I/P Converter

49. Generation and distribution of pneumatic pressure Compressor is needed for pneumatic system compressor 100 psi PS PC 30 psi Regulator valve To I/P Tank

50. Hydraulic Actuator

55. Advantage ELECTRICPNEUMATICHYDRAULIC Accurate position Suit to advance control No tubing Inexpensive Fast No pollution No return line No stall damage Large capacity Locking capability Self lubricating Easy to control Smooth operation Low speed Expensive Unsafe Need brake overheating Low accuracy Noise pollution Difficult speed control Need infrastructure Expensive Leakage problems Difficult speed control Need return line Need infrastructure Disadvantage