For class use only ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY Course No. FDEN-321 Course Title: INSTRUMENTATION & PROCESS CONTROL Credits: 3 (2 + 1) Prepared by Er. B. SREENIVASULA REDDY Assistant Professor (Food Engineering) College of Food Science and Technology Chinnarangapuram, Pulivendula – 516390 YSR (KADAPA) District, Andhra Pradesh DEPARTMENT OF FOOD ENGINEERING 1 Course No : FDEN - 321 2 Title : INSTRUMENTATION & PROCESS CONTROL 3 Credit hours : 3 (2+1) 4 General Objective : To impart knowledge to the students on instrumentation and process controls used in food industry 5 Specific Objectives : a) Theory : By the end of the course the students will be able to i) understand the different instruments used in different operations of food industries ii) know about working principles of different instruments used in different operations b) Practical By the end of the practical exercises the student will be able to i) identify different instruments and controls used in various operations ii) identify and tackle the problems encountered in use and operation of different instruments A) Theory Lecture Outlines 1 Introduction – Instrumentation, Process Control - measurements - methods of measurements - Direct Methods-In-Direct Methods 2 Primary measurements - secondary measurements - tertiary measurement -instruments and measurement systems - mechanical instruments - electrical instruments - electronic instruments 3 Functional elements of measurement systems - basic functional elements – auxiliary elements - transducer elements - examples of transducer elements 4 Linear variable differential transformer (LVDT) - advantages of LVDT - disadvantages of LVDT. 5 Classification of Instruments: Deflection and Null Types, Manually 2 Operated and Automatic Types, Analog and Digital Types, Self- Generating and Power-Operated Types, Contacting and Non-Contacting Types, Dumb and Intelligent Types 6 Indicating, recording and display elements: introduction-Digital voltmeters (DVMs), cathode ray oscilloscope (CRO), galvanometric recorders, magnetic tape recorders, digital recorder of memory type, data acquisition systems, data display and storage 7 Errors in Performance Parameters: Types of Errors, Systematic or Cumulative Errors, Accidental or Random Errors, Miscellaneous Type of Gross Errors 8 Characteristics of transducer elements - signal conditioning elements – amplification - Signal filtration 9 Standards of measurements - international standards - primary standards – secondary standards - working standards - calibration - classification of calibration 10 Performance characteristics - static and dynamic performance characteristics – accuracy - precession - resolution - threshold - static sensitivity - deflection factor 11 Performance characteristics- Linearity, Range and Span, Hysteresis, Dead Band, Backlash, Drift 12 Primary sensing elements - mechanical devices as primary detectors - springs, bimetallic strips - mechanical spring devices - cantilever - helical spring - spiral spring - torsion bar - proving ring 13 Pressure sensitive primary devices: Some of the commonly used force summing devices, Bourdon tubes, Diaphragms and Bellows 14 Temperature Measurement : Introduction- temperature scales- International Practical Temperature Scale (IPTS) 15 Measurement of Temperature: Classification of temperature measuring devices - bimetallic thermometers - glass thermometers and pressure gauge thermometers - thermocouples 16 Electrical resistance thermometers - Resistance- Temperature Detectors (RTDs)- Thermocouple - Thermocouple Materials 3 17 Pressure - gauge pressure, absolute pressure, differential pressure, vacuum - units of pressure - pressure scales - conversion of units- Types of Pressure Measurement Devices 18 Measurement of pressure : Manometers - U tube manometer - inclined tube manometer - well type manometer - Properties of Manometric Fluids 19 Elastic Pressure Elements - bourdon tube – bellows - diaphragms 20 Types of Fluid Flow : Steady flow and Unsteady flow- Uniform flow and Non-uniform flow - One-dimensional flow, two dimensional flow and Three dimensional flow- Rotational flow and Irrotational flow - Laminar flow and Turbulent flow. 21 Flow measurement : introduction - primary or quantity meters - positive- displacement meters - secondary or rate meters - variable head meters 22 The general expression for the rate of flow- Construction of Venturi Meter 23 Construction of Orifice Meter 24 Variable Area Meters- Rotameter; Pitot tube - its advantages - its limitations 25 Variable Head and Variable Area Flow Meters (Weirs) - Hot Wire Anemometers - Rotary Vane Meter 26 Measurement of Liquid Level - Direct Liquid Level Measurements - Dip- stick Method- Sight Glass Method- 27 Hook Gauge- Float Gauge - Float-and-Shaft Liquid Level Gauge 28 Indirect Liquid Level Measurements - Hydrostatic Pressure Level Measurement Device - Bubbler or Purge Technique for Level Measurement 29 Capacitance Level Gauge - Ultrasonic Level Gauge - Nucleonic Gauge 30 Control Systems- Introduction- Basic components of the control system- Classification of Control Systems – Open Loop System - Closed Loop System - Servo Mechanisms 31 Controllers and Control Action - Pneumatic Controller - Hydraulic Controllers - Electric Controllers 32 Data Transmission Elements - Electrical Type Data Transmission Elements - Pneumatic-Type Transmission Elements - Position-Type Data 4 Transmission Elements - Radio-Frequency (RF) Transmission System B) Practical Class Outlines 1 Study of instrumentation symbols 2 Measurement of temperature by different thermometers 3 Measurement of pressure by U tube manometer (inclined tube manometer) 4 Measurement of liquid level in the tank with the help of Bob and tape 5 Determination of relative humidity by wet and dry bulb thermometer 6 Measurement of velocity of fluid by using venturi meter/orifice meter/pitot tube 7 Measurement of RPM of an electric motor by tachometer 8 Measurement of wind velocity by anemometer 9 Measurement of intensity of sunshine by sunshine recorder 10 Characteristic of valve PI performance, T, P flow and level close leep control system 11 Measurement of viscosity 12 Calibration of common digital balance 13 Calibration and measurement of OD using spectrophotometer 14 Measurement of running fluid using rotameter 15 Measurement of vacuum - I 16 Measurement of vacuum - II References 1 B.C. Nakra and K.K.Chaudhary, Instrumentation Measurement and Analysis. Tata Mc Graw Hill, New Delhi. 2 Sahney and Sahney, A Course in Mechanical Measurement & Instrumentation. Dhanpat Rai and Sons, New Delhi. 3 K. Krishnaswamy and S. Vijayachitra, Industrial Instrumentation. New Age International (P) Limited, New Delhi. 5 LECTURE NO.1 INTRODUCTION – INSTRUMENTATION, PROCESS CONTROL - MEASUREMENTS - METHODS OF MEASUREMENTS - DIRECT METHODS- IN-DIRECT METHODS Instrumentation Instrumentation is defined as "the art and science of measurement and control". Instrumentation can be used to refer to the field in which Instrument technicians and engineers work in, or it can refer to the available methods and use of instruments. Instruments are devices which are used to measure attributes of physical systems. The variable measured can include practically any measurable variable related to the physical sciences. These variables commonly include: pressure , flow , temperature , level , density , viscosity , radiation , current , voltage , inductance , capacitance , frequency ,chemical composition , chemical properties , various physical properties, etc. Instruments can often be viewed in terms of a simple input-output device. For example, if we "input" some temperature into a thermocouple, it "outputs" some sort of signal. (Which can later be translated into data.) In the case of this thermocouple, it will "output" a signal in millivolts. Process control The purpose of process control is to reduce the variability in final products so that legislative requirements and consumers’ expectations of product quality and safety are met. It also aims to reduce wastage and production costs by improving the efficiency of processing. Simple control methods (for example, reading thermometers, noting liquid levels in tanks, adjusting valves to control the rate of heating or filling), have always been in place, but they have grown more sophisticated as the scale and complexity of processing has increased. With increased mechanization, more valves need to be opened and more motors started or stopped. The timing and sequencing of these activities has become more critical and any errors by operators has led to 6 more serious quality loss and financial consequences. This has caused a move away from controls based on the operators’ skill and judgment to technology- based control systems. Initially, manually operated valves were replaced by electric or pneumatic operation and switches for motors were relocated onto control panels. Measurements of process variables, such as levels of liquids in tanks, pressures, pH, temperatures, etc., were no longer taken at the site of equipment, but were sent by transmitters to control panels and gradually processes became more automated. Automatic control has been developed and applied in almost every sector of the industry. The impetus for these changes has come from: • increased competition that forces manufacturers to produce a wider variety of products more quickly • escalating labour costs and raw material costs • increasingly stringent regulations that have resulted from increasing consumer demands for standardized, safe foods and international harmonization of legislation and standards. For some products, new laws require monitoring, reporting and traceability of all batches produced which has further increased the need for more sophisticated process control. All of these requirements have caused manufacturers to upgrade the effectiveness of their process control and management systems. Advances in microelectronics and developments in computer software technology, together with the steady reduction in the cost of computing power, have led to the development of very fast data processing. This has in turn led to efficient, sophisticated, interlinked, more operator-friendly and affordable process control systems being made available to manufacturers. These developments are now used at all stages in a manufacturing process, including: • ordering and supplying raw materials • detailed production planning and supervision • management of orders, recipes and batches 7 • controlling the flow of product through the process • controlling process conditions • evaluation of process and product data (for example, monitoring temperature profiles during heat processing or chilling • control of cleaning-in-place procedures • packaging, warehouse storage and distribution. MEASUREMENTS Measurements provide us with a means of describing various phenomena in quantitative terms. It has been quoted "whatever exists, exists in some amount". The determination of the amount is measurement all about. There are innumerable things in nature which have amounts. The determination of their amounts constitutes the subject of Mechanical Measurements. The measurements are not necessarily carried out by purely mechanical means. Quantities like pressure, temperature, displacement, fluid flow and associated parameters, acoustics and related parameters, and fundamental quantities like mass, length, and time are typical of those which are within the scope of mechanical measurements. However, in many situations, these quantities are not measured by purely mechanical means, but more often are measured by electrical means by transducing them into an analogous electrical quantity. The Measurement of a given quantity is essentially an act or result of comparison between a quantity whose magnitude (amount) is unknown, with a similar quantity whose magnitude (amount) is known, the latter quantity being called a Standard. Since the two quantities, the amount of which is unknown and another quantity whose amount is known are compared, the result is expressed in terms of a numerical value. This is shown in the Fig. 1.1. 8 Fig. 1.1 Fundamental Measuring Process. In order that the results of measurement are meaningful, the basic requirements are: (i) the standard used for comparison purposes must be accurately defined and should be commonly acceptable, (ii) the standard must be of the same character as the measurand (the unknown quantity or the quantity under measurement). (iii) the apparatus used and the method adopted for the purposes of comparison must be provable. METHODS OF MEASUREMENT The methods of measurement may be broadly classified into two categories: Direct Methods. In-Direct Methods. Direct Methods. In these methods, the unknown quantity (also called the measurand) is directly compared against a standard. The result is expressed as a numerical number and a unit. Direct methods are quite common for the measurement of physical quantities like length, mass and time. Indirect Methods Measurements by direct methods are not always possible, feasible and, practicable. These methods in most of the cases, are inaccurate because they involve human factors. They are also less sensitive. Hence direct methods are not preferred and are less commonly used. In engineering applications Measurement Systems are used. These measurement systems use indirect methods for measurement purposes. A measurement system consists of a transducing element which converts the quantity to be measured into an analogous signal. The analogous 9 signal is then processed by some intermediate means and is then fed to the end devices which present the results of the measurement. 10