Week 8 - PLC/Pneumatic Interfacing PDF

ESET 225 PLC/Pneumatic Interfacing Agenda WEEK # 8  Fundamentals of Process Control Theory: Basic Control Concepts 1 ESET225- Future Labs Week 9: Lab 5 Find Analog min/max values Week 10: Lab 6 Analog input / output scaling Week 11: Lab 7 Pressure control Week 12: Open Lab Week 13: Lab Test during...

ESET 225 PLC/Pneumatic Interfacing Agenda WEEK # 8  Fundamentals of Process Control Theory: Basic Control Concepts 1 ESET225- Future Labs Week 9: Lab 5 Find Analog min/max values Week 10: Lab 6 Analog input / output scaling Week 11: Lab 7 Pressure control Week 12: Open Lab Week 13: Lab Test during regular lab class. 2 Energy System Engineering 1 Process Control Definition The process of observing a parameter, comparing it against a desired value, and the action to bring the parameter as close as possible to the desired value. value Three terms that are associated with any process: Controlled quantities Manipulated quantities disturbances Disturbances manipulated quantities process controlled quantities 3 Process Control Manual Control The operator is able to inspect the indicator visually and manipulate a flow into the process to achieve some desired value or set point of the controlled variable. 4 Energy System Engineering 2 Process Control Feedback Control Sensors measure the actual values of the controlled variables. The feedback control hardware automatically compares the set points of the controlled variables and the measured values of the same variables. Based on the difference the feedback control hardware calculates signals that reflect the needed values of the manipulated variables. 5 Process Control Elements of a Control System 1. Process A process consists of an assembly of equipment and material that relates to some manufacturing sequence. MEASUREMENT PROCESS SET POINT CONTROLLER CONTROL ELEMENT 6 Energy System Engineering 3 Process Control Elements of a Control System 1. Process 2. Measurement The conversion of a variable into an analog signal. Transducers Voltage Current 1. 2. 3. 4. Level Temperature Pressure Flow 7 Process Control Elements of a Control System 1. Process 2. Measurement 3. Evaluation Examines the measurement corrective action to be taken. MEASUREMENT SET POINT CONTROLLER and determines the Manual - operator Automatic Processing - electronic signal - computer - PLC CONTROL ELEMENT 8 Energy System Engineering 4 Process Control Elements of a Control System 1. Process 2. Measurement 3. Evaluation 4. Final Control Element The device that exerts a direct influence on the process. CONTROLLER CONTROL ELEMENT Control Valve Pump Motor Actuator PROCESS 9 Process Control Elements of a Control System 1. Process : Pressure Control 2. Measurement : Pressure Transducer- Analog Input 3. Evaluation: PLC program g 4. Final Control Element: Pressure regulatorAnalog output 10 Energy System Engineering 5 Process Control Set Up in E1-17 SMC Pressure Regulator (ITV) Provide P id liliner output pressure 0 to 130 PSI b based d on the Input current 4 to 20 mA Provide output signal 4 to 20 mA based on out pressure sensed. AB Analog Input and Output card 11 SMC Pressure Regulator 12 Energy System Engineering 6 SMC Pressure Regulator 13 SMC Pressure Regulator Provide liner output pressure 0 to 130 PSI based on the Input current 4 to 20 mA 14 Energy System Engineering 7 SMC Pressure Regulator 15 SMC Pressure Regulator Connection for Analog Input signal to regulator for changing output pressure 16 Energy System Engineering 8 SMC Pressure Regulator Connection for Analog Output signal from regulator to measure current output pressure. 17 Process Control Pneumatic Schematic Spring Return Cylinder Pressure Source Pressure Regulator 18 Energy System Engineering 9 AB Analog Modules The 1746-NIO4I is the Analog Combination I/O modules provide two input and two output channels in a single slot module. The 1746-NIO4I module contains two current inputs and two current outputs. 19 AB Analog Modules 20 Energy System Engineering 10 Process Control Electrical Layout 24 VDC Power Supply Analog I/O Module Pressure Regulator 21 Process Control Analog Inputs / Outputs Analog g inputs p convert current and voltage g signals g into 16–bit (max.) integer values and place them in the input image for the slot that the analog card is in. Analog outputs convert 16-bit integer values placed in the output image to voltage or current signals for the slot that the analog card is in. 22 Energy System Engineering 11 Analog Inputs / Outputs 23 Process Control 24 Energy System Engineering 12 Analog Signal Conversion OR Scaling  Analog signals received by the PLC appears as an integer in PLC units  This is not particularly useful to us as the number has no meaning without units we understand  We must convert the analog signal into a number that we can understand and use; such as PSI, Bar, MPa etc.  This can be accomplished through a linear mathematical equation: y=mx+b 25 Analog Signal Conversion OR Scaling 26 Energy System Engineering 13 Analog Signal Conversion OR Scaling  CPT Instruction  We need the following g instructions to complete p the analog conversion  CPT: the compute instruction. This instruction takes an equation entered by the user and generates an output based on the variables entered, then stores the result in a destination file  The CPT instruction will only generate outputs if all input conditions on the rung are true. Our application will require continuous calculation so the CPT instruction will be on at all times 27 Analog Signal Conversion OR Scaling  So, how do we convert?  Use the CPT instruction to p perform a calculation using g this formula: y=mx+b  y = analog signal after conversion; this is the output from the CPT instruction that is saved to the destination file; the value here represents the analog value in units we understand. (note: 'y' is the output and does not have to be entered))  m = slope of the line (you will need to calculate this)  x = analog input signal from sensor  b = a constant (you will need to calculate this) 28 Energy System Engineering 14 Analog Signal Conversion OR Scaling  As you can see we are missing the ‘m' and ‘b' values  We need two defined points to calculate these  We can do this by finding the analog input signal value at maximum and minimum pressure.  Then we can calculate the slope (m), and then the constant (b)  Example: At 0 PSI = PLC value is 4000 At 50 PSI = PLC value is 7500 29 Analog Signal Conversion OR Scaling m 50  0 50   0.0142 7500  4000 3500 0  0.0142 * 4000  b 0  57.14  b b  57.14 57 14 y  0.0142 (x)  57.14 30 Energy System Engineering 15 Analog Signal Conversion OR Scaling Using the converted signal  Once O we calculate l l t the th slope l ( ) and (m) d the th constant (b) we can enter the complete equation into the CPT instruction  Once online the CPT instruction will now generate an output that represents the analog input in the PSI units we understand. understand This output also represents the actual pressure in the cylinder 31 Analog Signal Conversion OR Scaling  SCP = Scale with Parameters  SCP instruction is used to produce a scaled output value that has a linear relationship between the input and scaled values. 32 Energy System Engineering 16 Test # 2  March 22, 2017  Lecture Week # 5 to 9  Labs 1 to 5 33 Energy System Engineering 17 ESET 225 PLC/Pneumatic Interfacing Agenda WEEK # 8 IEC 61131 3 Purpose of IEC 61131-3 International Electro technical Commission.  The first real attempt to standardize programming languages for industrial automation.  The great variety of available concepts led to an incompatibility between systems on different PLC platforms from various manufacturers in the past. This resulted in high costs for hardware, software and training.  IEC 61131 standardizes the programming languages, the interfaces between PLC and programming system, the different sets of instructions and the handling and structuring of projects.  The advantage of using IEC 61131-compliant PLCs and programming systems is a portability of all platforms and the use of same concepts. This reduces effort and cost for automation systems.  World wide support, independent of any single company. Standard Languages Textual – Instruction List (IL) – Structured Text (ST) Graphical – Ladder Diagram (LD) – Function Block Diagram (FBD) – Sequential Function Chart (SFC) 3 Instruction List Low level (= not user friendly) Similar to assembly language All other languages can be converted to IL Efficient, compact, fast programs can be developed by an experienced programmer 4 Energy System Engineering 2 Instruction List 5 Structured Text High level similar to Pascal or C Defined as language in which statements can be used to assign values to variables Program is built with expressions using a wide variety of statement types. 6 Energy System Engineering 3 Structured Text Example (If-Then-Else) IF I:0/0 AND !I:1/5 THEN N7:0 := 1; ELSIF I:0/2 OR (N7:5 (N7:6 * N7:2)) THEN N7:0 :=2; ELSIF !I:1/4 THEN N7 0 := 3 N7:0 3; ELSE N7:0 :=4; END_IF; 7 Ladder Diagram Most widely used programming language. Original method of programming PLCs Can be used in combination with any (or all) other types of programming 8 Energy System Engineering 4 Ladder Diagram 9 Function Block Diagram Very common in process industry. Expresses behavior of functions, function blocks and programs as a set of interconnected graphical blocks – Similar to electronic circuit diagrams Looks at system in terms of flow of signals between processing elements 10 Energy System Engineering 5 Function Block Diagram 11 Function vs Function Block Functions  Designed to perform common processing tasks: – Math and Trig – User defined  Take inputs and produce a result Function Blocks  Equivalent to special purpose IC  Contain C t i d data t as wellll as algorithm l ith – Can keep track of the past  Modular and independent 12 Energy System Engineering 6 Sequential Function Chart  Based on GRAFCET, with changes needed to convert from documentation standard to a set of execution control elements.  Can mix any of the other types of language – Function blocks can be step actions – Ladder logic can define transitions  Special variables defined  Redefined format for step actions 13 Sequential Function Chart 14 Energy System Engineering 7 15 Overview As IEC 1131-3 is implemented, the areas off application li ti are growing. i Benefits include: – Reduced waste of human resources – Increasing software reusability – Reducing misunderstandings and errors 16 Energy System Engineering 8