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CONTROL SYSTEM 1 (EIC - 501) (Session: 2014 – 15) Submitted By: Mr. Dheeraj Singh Mr. Mangal Das EC Department. ABES Engineering College Ghaziabad, U.P BASIC COMPONENTS OF CONTROL SYSTEM System – An interconnection of elements and devices for a desired purpose. Control System – An interconnection of components forming a system configuration that will provide a desired response. Process – The device, plant, or system under control. The input and output relationship represents the cause-and-effect relationship of the process. OPEN LOOP CONTROL SYSTEMS They are conditional control configurations formulated under the basic conditions that the system should not be subjected to any type of disturbances. Feedback is not Connected. More Stable than Closed loop systems because the effect of feedback is that it introduces delays or lags making the the speed of response of a closed loop system slow Performance analysis is not applicable to open loop systems because they are highly stable CLOSED LOOP SYSTEMS In this config. Changes in the output are measured through feedback & compared with Input or set point to achieve the control objective. Measurement or feedback in automatic control system is done using sensors or Transducers. Therefore feedback elements are measuring elements(Sensors or Transducers). EFFECTS OF FEEDBACK ON CONTROL SYSTEMS The reduction of system error is merely one of the many important effects that feedback may have upon a system. There are other important effects , such as stability, bandwidth, overall gain, disturbance, and sensitivity. If H=0 open loop system 1. Effect of Feedback on Overall Gain Open-loop gain = G Closed-loop gain = The general effect of feedback is that it may increase or decrease the gain G, and the gain of the system could increase in one frequency range but decrease in another. 2. Effect of Feedback on Stability If GH=-1, the system becomes unstable. Feedback can improve stability or be harmful to stability if it is not properly applied. 3. Effect of feedback on Sensitivity The sensitivity of the gain of the overall system M to the variation in G is defined as 4. Effect of feedback on External disturbance or noise. A good control system should be insensitive to noise and disturbances and sensitive to input commands. Consider the following system: TYPES OF FEEDBACK CONTROL SYSTEM BLOCK DIAGRAM REDUCTION TECHNIQUE SIGNAL FLOW GRAPH How to Obtain Transfer function using Mason’s Gain Formula Mechanical Systems All Mechanical Systems are classified into two types (1) Mech Translational System Input = Force(F) ; Output = Linear Disp or Linear Velocity The 3 – Ideal Elements (1) Mass Element M (a) F = M dv/dt X V F (b) F = Md2X/dt2 (2) Damper Element X1 V1 f or B F = f (V1 – V2) = fV F = f d (x1-x2) = fdx/dt F (3) Spring element F = K (X1 - X2 ) = KX F = K ᶴ (v1 – v2 ) dt X2 v2 MECHANICAL ROTATIONAL SYSTEM Input = Torque (T) ; The 3 ideal elements are (1) Inertia Element (2) Damper Torsional Element (3) Spring Torsional Element Output = Angular disp or Angular velocity ANALOGY BETWEEN MECHANICAL AND ELECTRICAL SYSTEM Electrical Quantity Mechanical Analog I (Force-Current) Mechanical Analog II (Force Voltage) Voltage, e Velocity, v Force, f Current, i Force, f Velocity, v Resistance, R Lubricity, 1/B (Inverse friction) Friction, B Capacitance, C Mass, M Compliance, 1/K (Inverse spring constant) Inductance, L Compliance, 1/K (Inverse spring constant) Mass, M Sensors and Encoders in Control Systems (i) Potentiometers A potentiometer is an electromechanical transducer that converts Mechanical Energy into electrical energy. Ks = Proportional Constant θc = shaft position Ckt Representation Tachometers Tachometers are electromechanical devices that convert mechanical energy Electrical energy. Velocity control System with tachometer feedback Position control system Tachometer feedback DC MOTORS IN CONTROL SYSTEM Basic operational principle Tm = Km ɸ Ia Tm = Motor Torque ɸ = Magnetic flux Ia = Armature current Km = Proportional constant Back emf eb = Kmɸωm ω = Shaft velocity Mathematical Modelling of DC motors Since ɸ is constant Ki = Torque Constant Block Diagram of DC Servo motor Thank You