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Automation and Drives - SCE
Training Document for Comprehensive Automation
Solutions
Totally Integrated Automation (T I A)
MODULE B3
Control Engineering with STEP 7
T I A Training Document Page 1 of 64 Module
B3
Issued: 02/2008 Control Engineering with STEP 7
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Automation and Drives - SCE This document has been written by Siemens AG for training purposes for the project entitled "Siemens Automation Cooperates with Education (SCE)". Siemens AG accepts no responsibility for the correctness of the contents. Transmission, use or reproduction of this document is only permitted within public training and educational facilities. Exceptions require the prio
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Automation and Drives - SCE Table of Contents PAGE 1. Preface 5 2. Fundamentals of Control Engineering 7 2.2 Components of a Control Loop 8 2.3. Characteristics 11 2.4 Step Function for Examining Controlled Systems 12 2.5. Self-Regulating Processes 13 2.5.1. Proportional Controlled System without Time Delay 13 2.5.2. Proportional Controlled System with a Time Delay 14 2.5.3 Proportional Controlled System with Two Time Delays 15 2.6 Controlled Systems without Inhe
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Automation and Drives - SCE The following symbols provide a guide through this B3 module: Information Programming Exercise Example Notes T I A Training Document Page 4 of 64 Module B3 Issued: 02/2008 Control Engineering with STEP 7
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Automation and Drives - SCE 1. PREFACE In terms of its contents, Module B3 is part of the teaching unit entitled "Additional Functions of STEP 7 Programming'. Basics of STEP 7 Programming 2 to 3 days Module A Additional Functions of Plant Simulation with STEP 7 Programming SIMIT SCE 2 to 3 days Module B 1 to 2 days Module G Programming Industrial Process Languages Field Bus Systems Visualization 2 to 3 days Module C 2 to
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Automation and Drives - SCE Hardware and software required 1 PC, operating system Windows 2000 Professional starting with SP4/XP Professional starting with SP1/Server 2003 with 600MHz and 512RAM, free hard disk storage 650 to 900 MB, MS Internet Explorer 6.0 2 Software STEP7 V 5.4 3 MPI interface for the PC (for example, PC adapter USB) 4 PLC SIMATIC S7-300 with at least one analog input/output module to which, at one analog value input, a potentiometer or another ana
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Automation and Drives - SCE 2. FUNDAMENTALS OF CONTROL ENGINEERING 2.1 Tasks of Control Engineering "Closed loop control is a process where the value of a variable is established and maintained continuously through intervention based on measurements of this variable. This creates a sequence that takes place in a controlled loop -the closed loop- because the process is executed based on measurements of a variable that is in turn influenced by itself.“ The variable
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Automation and Drives - SCE 2.2 Components of a Control Loop Below, the basic terminology of control engineering is explained in detail. First, an overview shown in the diagram below: Controller Final Controlled Controlling Comparing Control Actuator System Element Element Element Measuring Device 1. The Controlled Variable x It is the actual “objective“ of the control process: the variable that is to be influenced
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Automation and Drives - SCE 4. The Disturbance Variable z The disturbance variable is the variable that unintentionally influences the controlled variable, and moves it from the current setpoint value. A fixed setpoint control is necessary, for example, because a disturbance variable exists. For the heating system considered here, this would be the outside temperature, for example, or any other variable that changes the room temperature from its ideal value. 5. The Setp
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Automation and Drives - SCE 8. The Actuator The actuator is the “executing organ“, so to speak, of the control system. In the form of the controller output variable, the controlling element provides the actuator with information as to how the controlled variable is to be influenced, and implements it into a change of the “manipulated variable“. In our example, the actuator would be the mixer motor. Depending on the voltage supplied by the controlling element (that is, the
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Automation and Drives - SCE 2.3. Characteristics Controlled systems in which a new constant output value sets itself after a certain time has passed are called 'self-regulating process’. The relationship of the output variables to the input variables in the steady state results in a characteristic. Parameter In the environment of an operating point, the characteristic is replaced with a tangent. In the environment of
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Automation and Drives - SCE 2.4 Step Function for Examining Controlled Systems To examine the behavior of controlled systems, controllers and control loops, a uniform function is used for the input signal: the step function. Depending on whether a control loop element or the entire control loop is examined, the step function can be assigned to the following: the controlled variable x(t), the manipulated variable y(t), the reference variable w(t) or the disturbance varia
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Automation and Drives - SCE 2.5. Self-Regulating Processes 2.5.1. Proportional Controlled System without Time Delay The controlled system is called P-system for short. Abrupt change of the input variable for Controlled Variable/ pulated Variable Mani Proportional coefficient for a manipulated variable change Controlled Variable/ Disturbance Variable Proportional value for a
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Automation and Drives - SCE 2.5.2. Proportional Controlled System with a Time Delay The controlled system is called P-T1 system for short. Differential equation for a general input signal Solution of the differential equation for a step function at the input (step response) Time constant Preface Fundamentals Discontinuous Action Controller C
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Automation and Drives - SCE 2.5.3 Proportional Controlled System with Two Time Delays The controlled system is called P-T2 system for short. Figure: Jump Response of the P-T2 system Tu: Delay time Tg: Transition time The system consists of the reaction-free series connection of two P-T1 systems that have the time constants TS1 and TS2. Controllability of P-Tn systems: Can still be Easy to Difficult t
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Automation and Drives - SCE 2.5.4 Proportional Controlled System with n Time Delays The controlled system is called P-Tn system for short. The time response is described with a differential equation of the nth degree. The characteristic of the step response is similar to that of the P-T2 system. The time response is described through Tu and Tg. Substitute: The controlled system with many delays can be approximately substituted with the series connection of a P-T1 syste
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Automation and Drives - SCE 2.6 Controlled Systems without Inherent Regulation The controlled variable continues to grow after a fault, without aiming for the high range value. Example: Level Control In the case of a container with a drain whose inflow volume stream and outflow volume stream are the same, a constant level is the result. If the flow rate of the inflow or the outflow changes, the liquid level rises or falls. The larger the difference bet
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Automation and Drives - SCE 2.7 Types of Controllers 2.7.1 Two Position Controllers The essential feature of two position controllers consists of their knowing only two modes: “On“ and “Off“ -which makes them the simplest type of controller. Two-position controllers are used primarily when adhering to a setpoint exactly is less important than to keep the control system as simple as possible; or, when the actuator or the final control element does not allow for a cont
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Automation and Drives - SCE The diagram below shows a two position controller: Controlled Variable Switch-Off Value Hysteresis Setpoint Switch-On Value Manipulated Variable Time Time Preface Fundamentals Discontinuous Action Controller Controller Block (S)FB41 Setting the System Appendix T I A Training Document Page 19 of 64 Module B3 Issued: 02/2008
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Automation and Drives - SCE 2.7.2 Three Position Controllers The three position controllers represent the second important class of discrete controllers. The difference regarding the two position controllers consists in the following: The controller output can handle three different values: positive influence, no influence, and negative influence of the controlled variable. An example is control by means of a valve that can be adjusted electrically but that itself can on
