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Solution Manual for Sensors and Actuators: Engineering System Instrumentation, 2nd Edition

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    SOLUTIONS MANUAL FOR SENSORS AND ACTUATORS Engineering System Instrumentation SECOND EDITION Clarence W. de Silva by

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    iii CONTENTS Preface Chapter 1 Instrumentation of an Engineering System Chapter 2 Component Interconnection and Signal Conditioning Chapter 3 Performance Specification and Instrument Rating Parameters Chapter 4 Estimation from Measurements Chapter 5 Analog Sensors and Transducers Chapter 6 Digital and Innovative Sensing Chapter 7 Mechanical Transmission Components Chapter 8 Stepper Motors Chapter 9 Continuous-Drive Actuators

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    v PREFACE This manual is prepared primarily to assist the instructors who use the book SENSORS AND ACTUATORS — Engineering System Instrumentation, 2 nd Edition . It includes hints for structuring the material for a course in the subject and provides complete solutions to the end of chapter problems of the textbook. The book SENSORS AND ACTUATORS — Engineering System Instrumentation , 2 nd Edition , introduces the subject of Engineering System Instrumentation, with an emphasis on sensors, transducers, actuators, and signal modification devices. Specifically, it deal s with “instrumenting” an engineering system through the incorporation of suitable sensors, actuators, and associated interface hardware. It will serve as both a textbook for engineering students and a reference book for practicing professionals. As a textbook, it is suitable for courses in control system instrumentation; sensors and actuators; instrumentation of engineering systems; and mechatronics. There is adequate material in the book for two fourteen-week courses, one at the junior (third- year undergraduate) or senior (fourth-year undergraduate) level and the other at the first- year graduate level. In view of the practical considerations, design issues, and industrial techniques that are presented throughout the book, and in view of the simplified and snap-shot style presentation of more advanced theory and concepts, the book will serve as a useful reference tool for engineers, technicians, project managers, and other practicing professionals in industry and in research laboratories, in the fields of control engineering, mechanical engineering, electrical and computer engineering, manufacturing engineering, and mechatronics. The material presented in the book serves as a firm foundation, for subsequent building up of expertise in the subject — perhaps in an industrial setting or in an academic research laboratory — with further knowledge of hardware, software, and analytical skills (along with the essential hands-on experience) gained during the process. Undoubtedly, for best results, a course in sensors and actuators, mechatronics, or engineering system instrumentation should be accompanied by a laboratory component and class projects. Sensors are needed to measure (sense) unknown signals and parameters of an engineering system and its environment. This knowledge will be useful not only in operating or controlling the system but also for many other purposes such as process monitoring; experimental modeling (i.e., model identification); product testing and qualification; product quality assessment; fault prediction, detection and diagnosis; warning generation; and surveillance. Actuators are needed to “drive” a plant. As another category of actuators, control actuators perform control actions, and in particular they drive control devices. Since many different types and levels of signals are present in a dynamic system, signal modification (including signal conditioning and signal conversion) is indeed a crucial function associated with sensing and actuation. In particular, signal modification is an important consideration in component interfacing. It is clear that the subject of system instrumentation should deal with sensors, transducers, actuators, signal modification, and component interconnection. In particular, the subject should address the identification of the necessary system components with respect to type, functions, operation and interaction, and proper selection and interfacing of these components for various applications. Parameter selection (including component sizing and system tuning) is an important step as well. Design is a necessary part of system

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    vi instrumentation, for it is design that enables us to build a system that meets the performance requirements — starting, perhaps, with a few basic components such as sensors, actuators, controllers, compensators, and signal modification devices. The main objective of the book is to provide a foundation in all these important topics of engineering system instrumentation. A Note to the Instructors A syllabus for a fourth year undergraduate course or a first year graduate course in the subject is given below. CONTROL SENSORS AND ACTUATORS Prerequisites  For engineering graduate students: motivation  For undergraduate students: A course in feedback controls + consent of the instructor Introduction Actuators are needed to perform control “actions” as well as to directly “drive” a plant (process, machine, engine). Sensors and transducers are necessary to “measure” output signals for feedback control , to “measure” input signals for feedforward control , to “measure” process variables for system monitoring, d iagnosis and supervisory control, and for a variety of other purposes of measurement. The course will study a selected set of sensors, actuators, and signal modification devices as employed in robotic and mechatronic systems. General and practical issues of sensors and actuators in an engineering system will be discussed. Operating principles, modelling, design considerations, ratings, specifications, selection, and applications of typical sensors and actuators will be studied. Filtering amplification, error analysis, and estimation from measured data will be covered as complementary topics. Textbook De Silva, C.W., SENSORS AND ACTUATORS — Engineering System Instrumentation, Taylor & Francis, 2 nd Edition, Taylor & Francis/CRC Press, Boca Raton, FL, 2015.

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    vii Course Plan Week Starts on Topic Read 1 Jan. 06 Introduction Chapter 1 2 Jan. 13 P erformance Specification, Instrumentation of Engineering Systems Chapter 3 3 Jan. 20 Component Matching , Amplifiers, Filters, and Other Interface Hardware Chapter 2 4 Jan. 27 Estimation from Measured Data Chapter 4 5 Feb. 03 Analog Motion Sensors Chapter 5 6 Feb. 10 Project proposals due. Torque and Force Sensors Chapter 5 7 Feb. 17 Digital Motion Sensors , Tactile Sensors, and Innovative Sensors Chapter 6 8 Feb. 24 Mechanical Transmission Devices Chapter 7 9 Mar. 02 Stepper Motors Chapter 8 10 Mar. 09 DC and AC Motors Chapter 9 11 Mar. 16 (Exam on Mar. 16) Hydraulic Actuators Chapter 9 12 Mar. 23 Review Chapters 1 - 9 13 Mar. 30 Project presentations. 14 Apr. 6 Project presentations. Note : Final Take-Home Exam/Project Report due on April 12th. Grade Composition Intermediate exam = 30% Project proposal = 10% Attendance/Participation = 10% Final Take-Home Exam/Project = 50% 100% ==== Clarence W. de Silva Vancouver, Canada

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    Chapter 1 Instrumentation of an Engineering System Solution 1.1 Open-Loop Control System This d oes not use information on current response of the “plant” to establish the control action. E.g., so-called feed-forward control of a robot arm. The joint torques (or motor input signals) are computed using a dynamic model of the robot (inverse plant) with desired angles of rotation as inputs. These signals drive the joint motors, which in turn produce the actual joint angles. In the open-loop case these are not measured and feedback. Another example would be a household stove (gas or electric). The heat setting is manually selected. The actual heat flow is not measured. Feedback Control System This uses information on plant response to establish the control input. E.g., in feedback control of robot arms, joint angles (and angular velocities) are measured using suitable sensors (optical encoders, resolvers, pots, tachometers, RVDT’s, etc.). This information is used in feedback to compute the control action. In thermostatic control of temperature in a building, the temperature is measured, compared with the set point value (reference input) and the sign of the difference is used to turn on or shut off the heat source. Simple Oscillator: The oscillator (mass-spring- damper) is considered the plant in this case. The “apparent” feedback path (through k ) is a “natural” feedback within the plant. The response y is not sensed and used to determine f ( t ) to control the oscillator. Hence the system configuration is not a feedback control system. If, however, mass m is considered the plant, then the spring can be interpreted as a “passive” feedback element. The spring “senses” the position of the mass and feeds back a force to restore the position of the mass. In this sense it is a (passive) feedback control system. ___________________________________________________________________________ Solution 1.2 Lights On-off System for an Art Gallery There are two essential measurements in this system (a) Light intensity detection (b) People count. We should not measure the light intensity inside the gallery because there will be ambiguity as to the control action. Specifically, when the lights are on at night, the sensor would probably instruct the lights to be turned off thinking it is the day time because it could not differentiate between daylight and artificial light. To avoid this, a simple timer to indicate a rational time interval as the night time (e.g., 7:00 p.m. - 12:00

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    SENSORS AND ACTUATORS 2 midnight) could be used. Alternatively a photo-voltaic sensor could be installed outside the windows of the gallery or on top of a sunroof. People count has to be made directionally (i.e., entering or leaving) at each door. Hence a pair of probes is needed. Force sensors on the floor, turnstile counters, or light- pulse sensors may be used for this purpose. For example, consider the following arrangement: The light beams are generated by laser or LED visible-light sources. They are received by a pair of photo-voltaic cells. When the beam is intercepted for a short period of time, an output pulse is generated at the corresponding photo cell (see Figure S1.2(a). The order of the pulses determines the direction (entrance or exit) of travel. Even though measurements are made in the system, this is essentially an “open - loop” control system, as clear from the system schematic diagram shown in Figure S1.2(b). Figure S1.2: (a) People counting device; (b) Control system. The system output is the on/off status of the switch controlling the gallery lights. Even though the number of people in the gallery is counted and the light intensity is measured to control the switch, the status of the switch is not used to control the number of people in the gallery, or the day-light intensity. Hence there is no feedback path. 1 2 Output Pulses Photo-Voltaic Sensor Light-Beam Sources (a) Micro- controller Clock Pulse Pairs From Each Door ADC Signal From Light-Intensity Sensor DAC On/off Logic Amplifier, Solenoid On/off Switch (b)

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    CONTROL, INSTRUMENTATION, AND DESIGN 3 The operation of the control system is straightforward. The pulse signals from each door are detected and timed. This determines the people entering and leaving. A count (COUNT) is kept. Furthermore, the light intensity (INT) is measured and compared with a desired level (INTD). A logic circuit can be developed to realize the following logic:     . .0 . . . . LOGIC COUNT GT AND INT LT INTD  If this function is TRUE, the lights are turned on using a suitable actuator (e.g., a solenoid actuated by a current). Otherwise the lights are turned off. ___________________________________________________________________________ Solution 1.3 Component Component Type Stepper Motor Actuator PID Circuit Controller Power Amp Signal Modi fier ADC S ignal Modifier DAC Signal Modifier Optical Encoder Sensor/transducer Process Computer Controller FFT Analyzer Signal Modifier DSP Signal Modifier /Controller ___________________________________________________________________________ Solution 1.4 (a) Modeling errors, system parameter variations, random disturbances (b) Use feedback control. ___________________________________________________________________________ Solution 1.5 Advantages of Analog Control: Simple, extensive past experience is available, relatively easy to troubleshoot. Disadvantages of Analog Control: Assumes linear behavior (Coriolis and centrifugal forces, nonlinear damping, payload changes may be present, which are nonlinear) Bulky and costly. Difficult to implement complex control schemes.

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    SENSORS AND ACTUATORS 4 Tuning and adaptation cannot be carried out in real time. Not very flexible (not adaptable to different processes and process conditions). ___________________________________________________________________________ Solution 1.6 The schematic diagram of an automated bottle-filling system is shown in Figure S1.6. Figure S1.6: Schematic diagram of an automated bottle-filling system. The operation of the automated bottle-filling system can be described by the following series of steps: Container Full Level Sensor Empty Level Sensor Proximity Sensor (for Bottle Alignment) Nozzle Tank Valve Actuator Inlet Valve Controller Valve Actuator Exit Valve Conveyor M Motor Sensor Input Power

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    CONTROL, INSTRUMENTATION, AND DESIGN 5 1. When the power is on, the controller checks the sensor input to see (1) is the filling container full, and (2) is there an empty bottle under the nozzle? 2. If the first condition is not satisfied, the inlet valve is opened to fill the container until “ full container ” signal from the corresponding sensor is received. 3. If only the first condition is satisfied, the motor is activated to move an empty bottle under the nozzle. 4. The motor is stopped when “ bottle in position ” is detected (from the proximity sensor). 5. The exit valve is opened to fill the bottle. 6. When “ container is empty ” signal is received (from empty level sensor) the exit valve is closed. The motor is turned on again and the conveyor moves away the filled bottle. 7. Go to Step 1. The whole process is repeated again and again until either power is off or the “ process stop ” command is received by the controller. ___________________________________________________________________________ Solution 1.7 Note that one component may perform several functions. Controller: Thermostat Actuator: Valve actuator Sensor: Thermocouple, pilot flame detector Signal Modification: Transmitters and signal conditioning devices for thermostat signal to the valve, thermocouple signal, and pilot flame detector signal. Operation: The thermocouple measures the room temperature, compares it with the set point, and determines the error (= set point - actual temperature). If the error is positive, a signal is transmitted to turn on the natural gas valve. If negative, the valve is turned off. The pilot flame detector checks if the pilot flame is off. If so it overrides the actuator signal and turns off the valve. For better performance, measure the water flow rate, the inlet water temperature, and the outside temperature and incorporate a feedforward control as well as the original feedback scheme. In particular, the time delay in the process reaction can be considerably reduced by this method. Also a more sophisticated control scheme may be able to produce an improved temperature regulation, but it is not necessary in typical situations. ___________________________________________________________________________ Solution 1.8 (a) Load torque (using a dynamometer), or armature current of the dc motor (b) Input temperature of the liquid (using a hot-wire device) (c) Flow rate of the liquid (using a flow meter); Temperature outside the room (using a thermocouple); Temperature of steam at radiator input (d) Tactile forces at the gripper (using piezoelectric, capacitive or strain gauge sensors); Weight of the part to be picked up (e) Torque transmitted at manipulator joints (using strain gauge torque sensor); Curvature of the seam contour (using image processing). ___________________________________________________________________________

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    SENSORS AND ACTUATORS 6 Solution 1.9 (a) Muscle contraction, body movements, body temperature, heart rate (b) Decisions, profits, finished products (c) Electric power, pollution rate. (d) Front wheel turn, direction of heading, noise level, pollution level. (e) Joint motions, position, velocity, acceleration, torque, end-effector motion. ___________________________________________________________________________ Solution 1.10 Lowest level: 1ms Highest level: 1 day 24 60 60sec    6 1 Hz 11 10 24 60 60       Hz By Shannon’s sampling the orem, control bandwidth may be taken as half this value. ___________________________________________________________________________ Solution 1.11 The key features of a modern day cost effective process controller are: (i) P rogrammability - This increases the flexibility of control by allowing different control algorithms to be implemented without the need to having to change any hardware. (ii) Modularity - Extensions or modifications to existing hardware is made least expensive by employing different modules of control units to carry out different tasks, rather than using an all-in-one approach. It also increases the reliability since the failure of one module does not affect the operation of others. Maintenance and repair become easier and faster. (i ii) General Purpose Hardware - Use of such components allows replacement easier and inexpensive. ___________________________________________________________________________ Solution 1.12 The programmable logic controller is an electronic device, which can switch on or off its outputs depending on the status of its inputs. The switching characteristics can be programmed to respond to almost any combination of input states. In Figure S1.12, a PLC is employed to sort fruits on a conveyor into various categories depending on their size and quality. At the feeding end of the conveyor is a camera, which captures images of the incoming fruits and sends them to the image processing station for analysis. The output of

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    CONTROL, INSTRUMENTATION, AND DESIGN 7 Image Processing Station Programmable Logic Controller Size Attributes (On/Off) Quality Attributes (On/Off) Trigger Synchronizing Signal Gate Control Signals (On/Off) Solenoids For Gate Control Conveyor Camera the image processor is a series of two state signals, each of which has a single attribute of either size or quality, associated with it. That is, for each sample of fruit, only one size attribute signal and only one quality attribute signal can be in the ON state, and all other attribute signals must be in the OFF state. The PLC is programmed to switch ON one of its outputs for a particular combination of its inputs. A series of such outputs drive, through amplifiers (not shown), separate solenoids, which control the output ports for fruits. The whole arrangement is synchronized by the PLC through a signal derived from an object sensing device on the conveyor. Figure S1.12: An automated grading system for fruit. ___________________________________________________________________________ Solution 1.13 Measure inputs for feedforward control. Measure outputs for system monitoring, failure detection, and diagnosis. Measure signals for security (safety) reasons and to sound an alarm. Measure outputs during the teach mode and store for use in the repeat mode, in teach/repeat applications. 1. Detonation sensor 2. Hot film mass-flow sensor 3. Crack sensor 4. Throttle position sensor 5. Cam sensor

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    SENSORS AND ACTUATORS 8 Controller Sophistication PhysicalComplexity Passive Damper PID Controller Nonliner Feedback Controller Fuzzy Controller Impedance Cotnroller 6. Temperature sensor 7. Pressure sensor ___________________________________________________________________________ Solution 1.14 A graphical representation of controller classification is given in Figure S1.14. Figure S1.14: A graphical method of controller classification. ___________________________________________________________________________ Solution 1.15 By digital it does not mean that X-ray is not used. It implies that since the X-ray images are digitized and enhanced, lower X- ray levels can be used to obtain the images. So, the ‘digital” aspect enters not in the sensor but rather in the image representation and processing. ___________________________________________________________________________ Solution 1.16 Plant: Wood Drying Kiln Drying is the final process before the wood is available for general use, and to achieve the required serviceability in furniture manufacture, building, millwork and other wood product processes. The drying process is used to remove the moisture content of wood to assure high product quality, and is essential for imparting desirable properties to wood, including dimensional stability, workability, and hardening (e.g., as is required for tools), and promoting better absorption of treatments or adhesives. Properly dried wood provides a desirable surface texture as compared to wood that has not been dried, and can be machined

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    CONTROL, INSTRUMENTATION, AND DESIGN 9 or glued relatively easily. Moreover, drying of wood increases the strength, kills infestation, hardens pitch, preserves color, reduces weight (advantages in shipping and storing), and controls shrinkage. Fresh cut wood is dried in many different ways. The common commercial method is uses a wood-drying kiln, for accelerated drying. Kilns are perhaps the only practical means of rapid and high-volume drying of fresh forest lumber. Kilns are controlled enclosures used to dry products like lumber, poles, and raw materials such as the veneered wood and core fiber used in plywood panels. Stacks of wood are placed in the drying chamber (kiln) and the heated air is circulated through them. Typically, rail-mounted platforms carry the wood material in and out of a kiln. The kiln chamber is then sealed and heat is applied by steam or direct-fired air. Sometimes pressure or a vacuum is introduced into the chamber, depending on the product. The flow, temperature and humidity of the air have to be properly controlled in order to produce good drying results. Performance Requirements Typical kiln temperatures range between 200 and 230  F. While absolute estimates of the energy used in kiln drying are highly specific to the conditions of a given operation, engineering data indicate that steam applied and maintained at a temperature of near the 230  F limit permitted by the American National Standards Institute standard will apply heat to a product surface at a potential rate of roughly 22,000 Btu per square inch. Drying times generally vary from 1 to 6 days. Longer drying times are required for wood that receives oilborne or preservative treatments. Subjective anecdotal information indicates that the energy required to dry about 500 cubic feet of lumber from an as-received condition to a 20 % wet basis moisture content is approximately 10 million Btu. The specific application of wood is mainly determined by its final moisture content (m.c.) after drying. For example, an application like furniture making requires a final m.c. of 12% or lower. Quality of the dried lumber product is unpredictable, unreliable and non- repeatable. Kiln operators should frequently monitor the kiln operation and should make parameter adjustments as appropriate. Many years of experience would be required before an operator is given charge of carrying out these tasks. Problems can arise due to unattended operation during off-hours. The common practice of lowering the desired operating temperature during off-hours would lead to energy inefficiency. Also, an unexpected situation may occur during the unattended period, and may lead to undesirable defects in the drying boards. Furthermore, in view of the complexity, nonlinearity, and time-variant and distributed nature of the drying process, the quality of the dried wood may not be uniformly satisfactory in general. The fact that the drying results are unpredictable and that the entire process requires humans to close the control loop, provide an opportunity to use advanced technologies of sensing, actuation and control industrial kilns, with the goals of reducing the energy consumption and improving the quality of dried product. About 65% of the $250 billion/year forest product sales is attributed to lumber and various wood products. Innovations in sensing, actuation, and control can result in significant reductions in energy usage in kilns. The study summarized here provides an indication of the technologies that are appropriate and the energy savings that are possible.

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    SENSORS AND ACTUATORS 10 Constraints A conventional wood-drying kiln basically consists of electric coils for heating the air, which is circulated by rows of fans along the upper deck of the kiln. The heated, dry air is directed through the stacked lumber by a plenum chamber. The water removed from the wood is turned into water vapor by evaporation, and the saturated air is then released through air vents. A conventional kiln operates in an open-loop manner based on a pre-specified drying schedule. This process requires a full-time operator to frequently monitor and manually adjust all parameters according to the preset schedule. Due to the complex and distributed nature of the wood drying process, the end product is usually unpredictable, unreliable and unrepeatable. Energy efficient and automated lumber drying facilities are desirable. As well, the quality of the dried end product has to be acceptable, uniform, and repeatable. In summary, the following problems are faced by the existing conventional wood-drying kilns:  They operate according to a predetermined drying schedule;  They rely too heavily on experienced kiln operators for kiln configuration setting and for modification of the drying schedules;  They require dedicated attention of on-site operators;  They are left unattended during off-hours;  They are subjected to lower operating temperatures during off-hours in order to reduce the energy consumption; and are not monitored during unattended periods – possibly resulting in product defects; e.g., splits or cracks. Kiln drying is an energy-intensive process. In addition to the energy that is used for the drying process itself, some energy (electrical) is used for operating the fans in a kiln and for product repositioning during drying. The United States Department of Agriculture's Forest Product Laboratory research indicates that drying operations more commonly burn wood wastes rather than fossil fuels for their energy source. Proper air circulation and optimum temperature and residence schedules can result in significant reductions in kiln drying energy. In addition, Environmental concerns involve emissions from kilns, combustion systems, and treating agents. Waste heat from kilns can be recovered by means of heat exchangers. Wood-drying kilns have been suggested as a candidate technology using ground- source heat pumps for supplemental energy. These observations indicate that wood drying kilns provide a major opportunity for achieving significant benefits in energy efficiency through the use of advanced technology. Sensors Consider the prototype wood-drying kiln shown in Figure S1.16(a), which is a downscaled version of a conventional kiln that is used in industry, and has the dimensions of approximately 9 4 3   . The kiln has 12 thermocouples strategically positioned within it, to measure the kiln temperature; 2 relative humidity (RH%) sensors (wet-bulb/dry-bulb type), to measure the RH inside the kiln; one air velocity transmitter (hot-wire anemometer) to measure the air flow rate in the plenum; and 8 pairs of wood moisture content (MC) sensors that are nailed into the wood. Actuators The prototype kiln is equipped with a pulse-width-modulated (PWM) filament heater and a variable speed fan as the actuators for heating and air circulation.

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