FINALCONTROLELEMENT-JurusanTeknikElektrodan最终控制元件jurusanTeknik公司丹

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1、FINAL CONTROL ELEMENT,FINAL CONTROL ELEMENT,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,ELECTRIC FINAL CONTROL ELEMENT,Electric current/vol

2、tage Solenoid Stepping Motor DC Motor AC Motor,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 temperatu

3、re. Energy supplied by the heater element is W = i2rt (i=current, r=resistance, t=time) Motor is often used as device to control the speed,CHANGING CURRENT/VOLTAGE,Using Potentiometer Amplifier Ward Leonard system Switch (on-off action),Changing Current/VoltageUsing Rheostat,Rheostat,Heater,R1,R2,I

4、= V/(R1+R2) Power at rheostat P1 =I2R1 Power at heater P2 =I2R2 Disadvantage loss of power at rheostat,V,I,Example of Heating elements,Changing Current/VoltageUsing Amplifier,V,Potentiometer,R1,R2,amplifier,V+,V,Heater,Disadvantage loss of power at potentiometer (very small) and at Amplifier,Changin

5、g Current/VoltageUsing 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 pr

6、oduce wide range of voltage (0 to 3000V) Ward Leonard system is popular system to control the speed of big DC motor until 1980s Now a days semi conductors switches replaces this system,Changing Current/VoltageUsing Ward Leonard System,MOTOR,GENERATOR,excitation voltage,Changing Current/VoltageUsing

7、Switch,The switch is closed and opened repeatedly No power loss at switch,V,LOAD,Switch,t,VL,VL,V,Switch closed,Switch opened,DUTY CYCLE,T is period time typical in millisecond order (fix) Ton is switch on time (adjustable) Toff is switch off time Duty Cycle is: (Ton/T) 100%,t,VL,V,Ton,Toff,T,Of cou

8、rse 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),SOLENOID,When the coil is energized the core will be pulled in,SOLENOID,core,coil,coil,core,SOLENOID,

9、When the coil is energized the core will be pulled in,V,SIMULATE,SOLENOID,When the coil is energized the core will be pulled in,V,SIMULATE,SOLENOID,Tubular solenoid,Open frame solenoid,Rotary solenoid,Solenoid,Solenoid Usage,pushing buttons, hitting keys on a piano, Open closed Valve, Heavy duty con

10、tactor jumping robots etc,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 (

11、2) is energized, pulling the nearest teeth slightly to the right. This results in a rotation of 3.6 in this example.,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

12、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.,STEPPING MOTOR,Practical stepping motor can be controlled for full step and half step. Common typical step size is 1.8o for full

13、 step and 0.90 for half step Full step is accomplished by energizing 2 adjacent electromagnet simultaneously. Half step is accomplished by energizing 1 electromagnet at a time.,Stepping motor,DC Motor,The brush,DC Motor,Practical DC Motors,Every DC motor has six basic parts axle, rotor (a.k.a., arma

14、ture), stator, commutator, field magnet(s), and brushes.,For a small motor the magnets is made from permanent magnet,2 pole motor,Animate,2 pole motor,Animate,2 pole motor,Animate,2 pole motor,Animate,2 pole motor,Animate,2 pole motor,Animate,2 pole motor,Animate,2 pole motor,Animate,2 pole motor,An

15、imate,continue,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.,1,3,2,3 pole DC motors,animate,next,The commutator and the coil is arranged in such a way th

16、at the polarity of each pole is as shown,3 pole DC motors,animate,next,The commutator and the coil is arranged in such a way that the polarity of each pole is as shown,animate,next,The commutator and the coil is arranged in such a way that the polarity of each pole is as shown,3 pole DC motors,anima

17、te,next,3 pole DC motors,The commutator and the coil is arranged in such a way that the polarity of each pole is as shown,DC motors,As the rotor is rotating, back emf (Ea) will be produced, the faster the rotor turn the higher Ea and the smaller Ia. The starting current of motors will be much higher

18、 then the rating current.,motor,V,Ea,Ia,DC motors,For big motors the magnet is made from coil and core. The current flowing in the coil is called If and the current flowing in the armature is called Ia. The armature winding and the field winding are connected to a common power supply The armature wi

19、nding 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,SERIES DC MOTOR,Field and armature winding are series connected, this type of motor

20、 is called series DC motor,DC motors,Field and armature winding are parallel connected, this type of motor is called shunt DC motor,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,DC MOTOR,Tor

21、que: T = KIa K is a constant magnetic flux Ia is armature current Magnetic flux is constant if it is from permanent magnet It is depend on the If if it is produced by current,DC MOTOR TORQUE-SPEED CURVE,Torque: T = KIa,SERIES DC MOTOR TORQUE-SPEED CURVE,Torque: T = KIa T= KIa2,SHUNT DC MOTOR TORQUE-

22、SPEED CURVE,Torque: T = KIa,COMPOUND DC MOTOR TORQUE-SPEED CURVE,SYNCHRONOUS AC MOTOR,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,SYNCHRONOUS AC MOTOR,The rotating field. Whe

23、n alternating current is applied to the field coil the magnetic field will also alternating. Therefore the permanent magnet will rotate,o,311,-311,SYNCHRONOUS AC MOTOR,The rotating field. When alternating current is applied to the field coil the magnetic field will also alternating. Therefore the pe

24、rmanent magnet will rotate,o,311,-311,SYNCHRONOUS AC MOTOR,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,SYNCHRONOUS AC MOTOR,The rotating field. When alternating current is ap

25、plied to the field coil the magnetic field will also alternating. Therefore the permanent magnet will rotate,o,311,-311,SYNCHRONOUS AC MOTOR,The rotating field. When alternating current is applied to the field coil the magnetic field will also alternating. Therefore the permanent magnet will rotate,

26、o,311,-311,SYNCHRONOUS AC MOTOR,o,311,-311,This motor has 2 poles If the frequency of the current is f hertz (cycle/s) then the rpm n = f rps n = (120f)/p rpm Where p is the number of the poles,SYNCHRONOUS AC MOTOR,4 pole motor,THREE PHASE SYNCHRONOUS AC MOTOR,4 pole 3 motor,T,S,R,R,S,T,SYNCHRONOUS

27、AC MOTOR,SYNCHRONOUS AC MOTOR USING EXTERNAL EXITER,The magnetic flux of permanent magnet is low for a bigger motor we have to use externally exited magnetic field,ASYNCHRONOUS AC MOTOR,Iinduced,When instead of exited, the rotor coil is shorted an induced current will be generated and the rotor will

28、 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 i

29、nduction motor,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 Sr

30、pm = synchronous revolutions per minute.120 = constantF = 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 PSrpm = 120 x 60 4Srpm = 7200 4Srpm = 1800 rpm,Calculating Braking

31、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 horsepowerrpm = speed of mo

32、tor shaft Example: What is the braking torque of a 60 HP, 240V motor rotating at 1725 rpm? T = 5252 x HP rpmT = 5252 x 60 1725T = 315,120 1725T = 182.7 lb-ft,Calculating Work,Work is applying a force over a distance. Force is any cause that changes the position, motion, direction, or shape of an obj

33、ect. 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

34、)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 DW = 25 x 30W = 750 -lb,Pneumatic Actuator,Pneumatic Actuator,Reverse-Acting Actuator,I/P Converter,A current to press

35、ure 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

36、.,I/P,Air supply 30 psi,Current 4 to 20 mA,Pneumatic 3 to 15 psi Supplied to actuator,Sample of I/P Converter,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,Hydraulic Actuator,Hydraulic Actuator,Hydraulic Actuator,Advantage,Disadvantage,