lesson1et438a (1).ppsx
- 1. ET 438a Automatic Control Systems Technology Lesson 1: Introduction to Control Systems Technology 1 lesson1et438a.pptx
- 2. Learning Objectives lesson1et438a.pptx 2 After this presentation you will be able to: Explain the function of an automatic control system. Identify a block diagram representation of a physical system Explain the difference between an open loop and closed loop control system Define a transfer function and compute the gain for sinusoidal input/output cases. Reduce block diagram systems using algebra.
- 3. The Control Problem lesson1et438a.pptx 3 Fundamental Control Concepts h Maintain a variable of process at a desired value while rejecting the effects of outside disturbances by manipulating another system variable. Examples: Heating and Cooling homes and offices Automobile cruise control Hold the position of a mechanical linkage Maintain level in a tank Qout depends on h If Qout = Qin, h constant Qout > Qin, tank empties Qout < Qin, tank overflows
- 4. Basic Subsystems of Control lesson1et438a.pptx 4 Feedback Control Subsystems Measurement Control decision System modification Process- Maintain tank level Measureme nt- sight glass Final Control Element Valve Control Decision Human adjusts Qout to maintain h =H Reference (setpoint) h = control variable
- 5. Automatic Control Systems lesson1et438a.pptx 5 Sensor Controller Final control element Use sensors and analog or digital electronics to monitor and adju Elements of Automatic Control Process – single or multiple variables Measurement – sensors Error Detection – compare H to h Controller – generate corrections Final Control Element – modify process Maintain level Level Measureme nt Valve Position
- 6. Block Diagrams lesson1et438a.pptx 6 Automatic control systems use mathematical descriptions of subsystems to reduce complex components to inputs and outputs Control System Component Input signal Output signal Signals flow between components in system based on arrow di Energy Source (Optional)
- 7. Typical Component Block Diagrams lesson1et438a.pptx 7 Temperature Sensor T (°C) Vout (mV) Amplifier Vin (V) Vout (V) Dc Motor Armature V Va (V) n (rpm) Control Valve Valve Position (% Open) Liquid Flow (m3/s) Level Transmitter L (ft) Current (mA) Controller Error E (V) Correction V (V)
- 8. Transfer Functions lesson1et438a.pptx 8 Transfer function - ratio of the output to the input of a control system component. Generally a function of frequency and time. G A∙sin(wt+a) B∙sin(wt+b) Convert to phasors and divide a b a b A B A B Signal Input Signal Output A B G Block Gain Phase shift related to time delay
- 9. lesson1et438a.pptx 9 Transfer Functions Examples Temperature Sensor T (°C) Vout (mV) mV/C T V Signal Input Signal Output G out Example 1-1: Find transfer function of temperature sensor in block diagram Example 1-2: a current-to-voltage converter takes an input of 17.530° mA an an output of 8.3537° V Determine the transfer function gain and sketch the b A m V/ 7 477 . 0 G A m V/ mA 30 5 . 17 V 37 35 . 8 I V Signal Input Signal Output G V 37 35 . 8 V mA 30 5 . 17 I in o o in I-to-V Converter G Iin (mA) Vout (V)
- 10. Open-Loop Control lesson1et438a.pptx 10 Open loop control modifies output based on predetermined control values. There is no actual measurement of controlled quantity. Controller Final control element Control Valve Controlle r Valve setting Output flow Tank Tank Level Disturbances Tank level may vary with outside disturbances and system changes
- 11. Closed Loop Control lesson1et438a.pptx 11 Closed loop control modifies output based on measured values of the control variable. Measured value compared to desired value and used to maintain desired value when disturbances occur. Closed loop control uses feedback of output to input. Controller Control Valve Tank Level Measurem ent + - Desired Value Valve setting Output flow Measured level Tank Level
- 12. Closed Loop Control lesson1et438a.pptx 12 Example: Auto Cruise Control Set Speed Error Fuel flow Controlle r Fuel Injectors Auto Speed Sensor + - Engine Actual Speed Mechanic al Power Disturbances: Up hill/ down hill Head wind/ tail wind Disturbances
- 13. Generalized Closed Loop Control lesson1et438a.pptx 13 Block Diagram of Servo Control-Example Positioning Systems Reference = R Error = E Controlled Variable = C + - Controller G=C/E Measurement H=Cm/C R Cm C E=R-Cm Measured Variable = Cm
- 14. Generalized Closed Loop Control lesson1et438a.pptx 14 Find overall transfer function using signal flow algebra (Input)(Gain)=(Output) For servo control m C R E C G E E C G m m C H C C C H 1 2 3 R C Find 1 3 m C R E H C E C G H) C R (
- 15. Overall Transfer Function-Servo Control lesson1et438a.pptx 15 C G H C - G R C G H) C R ( R C Find R C ) H G 1 ( G C ) H G 1 ( G R ) H G 1 ( C G R G H C C G R 1 2 3 Multiply through by G Add CHG to both sides Factor C out of right hand side Divide both sides by (1+GH) Divide both sides by R
- 16. Generalized Closed Loop Control lesson1et438a.pptx 16 Block Diagram of Process Control-Example Chemical Reactors Measurement H=Cm/C Manipulate d Variable Gm=M/V + - Control Modes Gc=V/E Process Gp=C/M Setpoint = SP Error = E Controlled Variable = C SP Cm C E=R- Cm Measured Variable = Cm M Manipulated Variable = M Controller Output = V V D=Disturbances
- 17. Overall Transfer Function- Process Control lesson1et438a.pptx 17 Find overall transfer function of process control using signal flow Series blocks multiple M C G V M G E V G p m c M C V M E V G G G G p m c E C G Find overall transfer function Cm/SP C not directly measurable in process control
- 18. lesson1et438a.pptx 18 Overall Transfer Function- Process Control As before m C SP E C H C C H C m m m m m m m m m m m C H G C SP H G C C H G SP H G C ) C SP ( H G H C ) C SP ( G C ) C SP ( G C E G SP C H G 1 H G C H G 1 SP H G ) H G 1 ( C SP H G m m m Substitute in for E Substitute in for C eliminate it Multiple both sides by H Multiple L.H. side by GH Add GHCm to both sides Factor Cm from right side Divide both sides by (1+GH) Divide both sides by SP
- 19. Control System Drawings lesson1et438a.pptx 19 Industrial system standard ANSI/ISA-S5.1-1984 Uniform design Instruments, instrument systems and control. Functional Identifier General Instrument Symbol Loop Identifier Instrument Line Symbols 3-15 psi pneumatic line 4-20 mA electric current Filled System Capillary First ID Letter Following ID Letter A = Analysis C= Controller L = Level I=Indicator T = Temperature R=Recorder T= Transmitter V = Valve Y = Relay/Converter
- 20. Control System Drawings lesson1et438a.pptx 20 Heated Product Heating Fluid Return Heating Fluid Supply Water Supply Syrup Supply TIC 102 102 TT 102 TV LT LIC 101 101 LY 101 101 LV 103 AT 103 ARC 103 AV Syrup Concentration Current to Pneumatic Converter I/P 101 =level control 102 = temperature control 103 = concentration control Temperature Transmitter Concentration Valve Temperature Indicator/Control Concentration Recorder/Contr ol 4-20 mA current Concentration Transmitter
- 21. Linear and Non-linear Response lesson1et438a.pptx 21 1 0.5 0 0.5 1 2 0 2 Linear Response Input Output 15 10 5 0 5 10 15 2 0 2 Input Output Time Output Linear transfer functions give proportional outputs. In this case the factor is 2
- 22. Non-linear Response lesson1et438a.pptx 22 3 2 1 0 1 2 3 10 0 10 Saturation Non-Linearity Input Output 15 10 5 0 5 10 15 1 0 1 Input Signal Saturation Non-Linearity Time Input Signal 15 10 5 0 5 10 15 1 0 1 Output Signal Saturation Non-Linearity Time Output Signal Saturation non-linearity typical of practical systems that have physical limits. Amplifiers, control valves
- 23. Other Non-Linearities lesson1et438a.pptx 23 4 2 0 2 4 2 1 0 1 2 Hystersis Non-Linearity Input Output 3 2 1 0 1 2 3 40 20 0 20 40 General Non-Linearity Input Output Typical in magnetic circuit and in instrumentation transducers Non-linearities cause distortion in sine waves response that is not proportional to inputs va for all signal values.
- 24. Block Diagram Simplifications lesson1et438a.pptx 24 G H - + R C R C H G 1 G R C Block diagram at left simplifies to the above Can use this to reduce multiple loops into o Block. Also remember that blocks in series multiply G1 G2 G3 G1G2G3 3 2 1 G G G G Equivalent Block
- 25. Block Diagram Simplification Example lesson1et438a.pptx 25 G2 H1 - + + R - G1 G3 H3 H2 C R1 C1 1 2 2 1 1 H G 1 G R C H 3 2 H H H Reduce the inner loop Combine outer feedback block Combine reduced inner loop with remaining forward gain blocks
- 26. Block Diagram Simplification Example (1) lesson1et438a.pptx 26 + R - G1 G3 H=H2H3 C 1 2 2 H G 1 G 1 2 3 2 1 3 1 2 2 1 H G 1 G G G G H G 1 G G G Compute the value of G 3 2 1 2 3 2 1 1 2 3 2 1 H H H G 1 G G G 1 H G 1 G G G H G 1 G R C Substitute the values of G and H into formu and simplify
- 27. Block Diagram Simplification Example (2) lesson1et438a.pptx 27 3 2 1 2 3 2 1 1 2 3 2 1 H H H G 1 G G G 1 H G 1 G G G H G 1 G R C 1 2 3 2 3 2 1 1 2 1 2 3 2 1 1 2 3 2 1 2 3 2 1 1 2 1 2 3 2 1 H G 1 H H G G G H G 1 H G 1 G G G H G 1 H H H G 1 G G G 1 H G 1 H G 1 G G G R C 3 2 3 2 1 1 2 3 2 1 H H G G G H G 1 G G G R C Answer Multiply top and bottom of ratio by (1+G2H1) and simplify 3 2 3 2 1 1 2 3 2 1 H H G G G H G 1 G G G R C Reduced block
- 28. End Lesson 1: Introduction to Control Systems Technology ET 438a Automatic Control Systems Technology lesson1et438a.pptx 28