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

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SOLUTIONS MANUAL FORSENSORS ANDACTUATORSEngineering System InstrumentationSECOND EDITIONClarence W. de Silvaby

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iiiCONTENTSPrefaceChapter 1Instrumentation of an Engineering SystemChapter 2Component Interconnection and Signal ConditioningChapter 3Performance Specification and Instrument Rating ParametersChapter 4Estimation from MeasurementsChapter 5Analog Sensors and TransducersChapter 6Digital and Innovative SensingChapter 7Mechanical Transmission ComponentsChapter 8Stepper MotorsChapter 9Continuous-Drive Actuators

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vPREFACEThis manual is prepared primarily to assist the instructors who use the bookSENSORSAND ACTUATORS—Engineering System Instrumentation, 2ndEdition. It includes hintsfor structuring the material for a course in the subject and provides complete solutions tothe end of chapter problems of the textbook.The bookSENSORS AND ACTUATORS—Engineering System Instrumentation,2ndEdition, introduces the subject of Engineering System Instrumentation, with anemphasisonsensors,transducers,actuators,andsignalmodificationdevices.Specifically,itdealswith“instrumenting”anengineeringsystemthroughtheincorporation of suitable sensors, actuators, and associated interface hardware. It willserve as both a textbook for engineering students and a reference book for practicingprofessionals. As a textbook, it is suitable for courses in control system instrumentation;sensors and actuators; instrumentation of engineering systems; and mechatronics. Thereis 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 industrialtechniques that are presented throughout the book, and in view of the simplified andsnap-shot style presentation of more advanced theory and concepts, the book will serve asa useful reference tool for engineers, technicians, project managers, and other practicingprofessionals 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 subsequentbuilding up of expertise in the subject—perhaps in an industrial setting or in an academicresearch 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 systeminstrumentation should be accompanied by a laboratory component and class projects.Sensors are needed to measure (sense) unknown signals and parameters of anengineering system and its environment. This knowledge will be useful not only inoperating or controlling the system but also for many other purposes such as processmonitoring;experimentalmodeling(i.e.,modelidentification);producttesting andqualification;productquality assessment;faultprediction,detection and diagnosis;warning generation; and surveillance.Actuators are needed to “drive” a plant. As anothercategory of actuators,control actuatorsperform control actions, and in particular theydrive control devices. Since many different types and levels of signals are present in adynamicsystem,signalmodification(includingsignalconditioningandsignalconversion) is indeed a crucial function associated with sensing and actuation. Inparticular, signal modification is an important consideration in component interfacing. Itis clear that the subject of system instrumentation should deal with sensors, transducers,actuators, signal modification, and component interconnection. In particular, the subjectshould address the identification of the necessary system components with respect totype, functions, operation and interaction, and proper selection and interfacing of thesecomponents for various applications. Parameter selection (including component sizingand system tuning) is an important step as well. Design is a necessary part of system

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viinstrumentation, for it is design that enables us to build a system that meets theperformance requirements—starting, perhaps, with a few basic components such assensors, actuators, controllers, compensators, and signal modification devices. The mainobjective of the book is to provide a foundation in all these important topics ofengineering system instrumentation.A Note to the InstructorsA syllabus for a fourth year undergraduate course or a first year graduate course in thesubject is given below.CONTROL SENSORS AND ACTUATORSPrerequisitesFor engineering graduate students: motivationFor undergraduate students: A course in feedback controls+ consent of the instructorIntroductionActuators are needed to perform control “actions” as well as to directly “drive” a plant(process, machine, engine). Sensors and transducers are necessary to “measure” outputsignals forfeedback control, to “measure” input signals forfeedforward control, to“measure” process variables for system monitoring, diagnosis and supervisory control,and for a variety of other purposes of measurement.The course will study a selected set of sensors, actuators, and signal modificationdevices as employed in robotic and mechatronic systems. General and practical issues ofsensors and actuators in an engineering system will be discussed. Operating principles,modelling, design considerations, ratings, specifications, selection, and applications oftypical sensors and actuators will be studied. Filtering amplification, error analysis, andestimation from measured data will be covered as complementary topics.TextbookDe Silva, C.W.,SENSORS AND ACTUATORS—Engineering System Instrumentation,Taylor & Francis, 2ndEdition, Taylor & Francis/CRC Press, Boca Raton, FL, 2015.

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viiCourse PlanWeekStarts onTopicRead1Jan. 06IntroductionChapter 12Jan. 13Performance Specification,Instrumentation of EngineeringSystemsChapter 33Jan. 20Component Matching, Amplifiers,Filters, and Other Interface HardwareChapter 24Jan. 27Estimation from Measured DataChapter 45Feb. 03Analog Motion SensorsChapter 56Feb. 10Project proposals due.Torque andForceSensorsChapter 57Feb. 17Digital Motion Sensors, TactileSensors, and Innovative SensorsChapter 68Feb. 24Mechanical Transmission DevicesChapter 79Mar. 02Stepper MotorsChapter810Mar. 09DC and AC MotorsChapter 911Mar. 16(Exam on Mar. 16)Hydraulic ActuatorsChapter 912Mar. 23ReviewChapters 1-913Mar. 30Project presentations.14Apr. 6Project presentations.Note: Final Take-Home Exam/Project Report due on April 12th.Grade CompositionIntermediate exam=30%Project proposal=10%Attendance/Participation=10%Final Take-Home Exam/Project=50%100%====Clarence W. de SilvaVancouver, Canada

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Chapter 1 Instrumentation of an Engineering SystemSolution 1.1Open-Loop Control SystemThis does not use information on current response of the “plant” to establish the controlaction.E.g., so-called feed-forward control of a robot arm.The joint torques (or motorinput signals) are computed using a dynamic model of the robot (inverse plant) withdesired angles of rotation as inputs.These signals drive the joint motors, which in turnproduce the actual joint angles.In the open-loop case these are not measured andfeedback.Another example would be a household stove (gas or electric). The heat setting ismanually selected. The actual heat flow is not measured.Feedback Control SystemThis uses information on plant response to establish the control input.E.g., in feedbackcontrol of robot arms, joint angles (and angular velocities) are measured using suitablesensors (optical encoders, resolvers, pots, tachometers, RVDT’s, etc.).This informationis 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 usedto 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 (throughk) is a “natural” feedback within the plant.The responseyis notsensedandusedtodeterminef(t)tocontroltheoscillator.Hencethesystemconfiguration is not a feedback control system.If, however, massmis considered the plant, then the spring can be interpreted as a“passive” feedback element. The spring “senses” the position of the mass and feeds backa force to restore the position of the mass.In this sense it is a (passive) feedback controlsystem.___________________________________________________________________________Solution 1.2Lights On-off System for an Art GalleryThere 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 beambiguity as to the control action.Specifically, when the lights are on at night, thesensor would probably instruct the lights to be turned off thinking it is the day timebecause it could not differentiate between daylight and artificial light.To avoid this, asimple 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 ACTUATORS2midnight) could be used.Alternatively a photo-voltaic sensor could be installed outsidethe 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 followingarrangement:The light beams are generated by laser or LED visible-light sources.They are receivedby 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).Theorder of the pulses determines the direction (entrance or exit) of travel.Even though measurements are made in the system, this isessentially an “open-loop” control system, as clear from the system schematicdiagram shown in FigureS1.2(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.Eventhough the number of people in the gallery is counted and the light intensity is measuredto control the switch, the status of the switch is not used to control the number of peoplein the gallery, or the day-light intensity. Hence there is no feedback path.12Output PulsesPhoto-Voltaic SensorLight-BeamSources(a)Micro-controllerClockPulse PairsFrom EachDoorADCSignal FromLight-IntensitySensorDACOn/offLogicAmplifier,SolenoidOn/offSwitch(b)

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CONTROL, INSTRUMENTATION, AND DESIGN3The operation of the control system is straightforward.The pulse signals fromeach door are detected and timed.This determines the people entering and leaving.Acount(COUNT)iskept.Furthermore,thelightintensity(INT)ismeasuredandcompared with a desired level (INTD).A logic circuit can be developed to realize thefollowing logic:..0 ....LOGICCOUNT GTANDINT LT INTDIf this function is TRUE, the lights are turned on using a suitable actuator (e.g., asolenoid actuated by a current). Otherwise the lights are turned off.___________________________________________________________________________Solution 1.3ComponentComponentTypeStepperMotorActuatorPID CircuitControllerPower AmpSignal ModifierADCSignal ModifierDACSignal ModifierOptical EncoderSensor/transducerProcess ComputerControllerFFT AnalyzerSignal ModifierDSPSignal Modifier/Controller___________________________________________________________________________Solution 1.4(a)Modeling errors, system parameter variations, random disturbances(b)Use feedback control.___________________________________________________________________________Solution 1.5Advantages 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, payloadchanges may be present, which are nonlinear)Bulky and costly.Difficult to implement complex control schemes.

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SENSORS AND ACTUATORS4Tuning and adaptation cannot be carried out in real time.Not very flexible (not adaptable to different processes and process conditions).___________________________________________________________________________Solution 1.6The 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 followingseries of steps:ContainerFull Level SensorEmpty Level SensorProximity Sensor(for Bottle Alignment)NozzleTankValve ActuatorInlet ValveControllerValve ActuatorExit ValveConveyorMMotorSensorInputPower

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CONTROL, INSTRUMENTATION, AND DESIGN51.When the power is on, the controller checks the sensor input to see (1) is the fillingcontainer 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 bottleunder 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 isclosed. 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 orthe“process stop”command is received by the controller.___________________________________________________________________________Solution 1.7Note that one component may perform several functions.Controller: ThermostatActuator: Valve actuatorSensor: Thermocouple, pilot flame detectorSignal Modification: Transmitters and signal conditioning devices for thermostat signalto the valve, thermocouple signal, and pilot flame detector signal.Operation:The thermocouple measures the room temperature, compares it with the setpoint, 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 turnedoff.The pilot flame detector checks if the pilot flame is off.If so it overrides theactuator 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 originalfeedback scheme. In particular, the time delay in the process reaction can be considerablyreduced by this method. Also a more sophisticated control scheme may be able toproduce 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 athermocouple); 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); Curvatureof the seam contour (using image processing).___________________________________________________________________________

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SENSORS AND ACTUATORS6Solution 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 1.10Lowest level: 1msHighest level:1 day246060sec61Hz11 10246060HzBy Shannon’s sampling theorem, control bandwidth may be taken as half this value.___________________________________________________________________________Solution 1.11The key features of a modern day cost effective process controller are:(i)Programmability-This increases the flexibility of control by allowingdifferent control algorithms to be implemented withoutthe need to having to change any hardware.(ii)Modularity-Extensions or modifications to existing hardware ismade least expensive by employing different modules ofcontrol units to carry out different tasks, rather than usingan all-in-one approach.It also increases the reliabilitysince the failure of one module does notaffecttheoperationofothers.Maintenanceandrepairbecomeeasier and faster.(iii)GeneralPurpose Hardware-Use of such components allows replacement easierand inexpensive.___________________________________________________________________________Solution 1.12The programmable logic controller is an electronic device, which can switch on or off itsoutputsdependingonthestatusofitsinputs.Theswitchingcharacteristicscanbeprogrammed to respond to almost any combination of input states. In Figure S1.12, a PLC isemployed to sort fruits on a conveyor into various categories depending on their size andquality.At the feeding end of the conveyor is a camera, which captures images of theincoming fruits and sends them to the image processing station for analysis.The output of

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CONTROL, INSTRUMENTATION, AND DESIGN7ImageProcessingStationProgrammableLogic ControllerSize Attributes (On/Off)Quality Attributes (On/Off)TriggerSynchronizing SignalGate Control Signals (On/Off)Solenoids ForGate ControlConveyorCamerathe image processor is a series of two state signals, each of which has a single attribute ofeither size or quality, associated with it.That is, for each sample of fruit, only one sizeattribute signal and only one quality attribute signal can be in the ON state, and all otherattribute signals must be in the OFF state. The PLC is programmed to switch ON one of itsoutputs for a particular combination of its inputs.A series of such outputs drive, throughamplifiers (not shown), separate solenoids, which control the output ports for fruits.Thewhole arrangement is synchronized by the PLC through a signal derived from an objectsensing device on the conveyor.Figure S1.12: An automated grading system for fruit.___________________________________________________________________________Solution 1.13Measure 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, inteach/repeat applications.1.Detonation sensor2.Hot film mass-flow sensor3.Crack sensor4.Throttle position sensor5.Cam sensor

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SENSORS AND ACTUATORS8ControllerSophisticationPhysicalComplexityPassiveDamperPIDControllerNonliner FeedbackControllerFuzzyControllerImpedanceCotnroller6.Temperature sensor7.Pressure sensor___________________________________________________________________________Solution 1.14A graphical representation of controller classification is given in Figure S1.14.Figure S1.14: A graphical method of controller classification.___________________________________________________________________________Solution 1.15By digital it does not mean that X-ray is not used. It implies that since the X-ray images aredigitized 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 1.16Plant: Wood Drying KilnDrying is the final process before the wood is available for general use, and to achieve therequired serviceability in furniture manufacture, building, millwork and other wood productprocesses. The drying process is used to remove the moisture content of wood to assure highproduct quality, and is essential for imparting desirable properties to wood, includingdimensionalstability,workability,andhardening(e.g.,asisrequiredfortools),andpromoting better absorption of treatments or adhesives. Properly dried wood provides adesirable surface texture as compared to wood that has not been dried, and can be machined

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CONTROL, INSTRUMENTATION, AND DESIGN9or glued relatively easily. Moreover, drying of wood increases the strength, kills infestation,hardens pitch, preserves color, reduces weight (advantages in shipping and storing), andcontrolsshrinkage.Freshcutwoodisdriedinmanydifferentways.Thecommoncommercial method is uses a wood-drying kiln, for accelerated drying.Kilns are perhaps the only practical means of rapid and high-volume drying of freshforest lumber. Kilns are controlled enclosures used to dry products like lumber, poles, andraw materials such as the veneered wood and core fiber used in plywood panels. Stacks ofwood 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 kilnchamber is then sealed and heat is applied by steam or direct-fired air. Sometimes pressure ora vacuum is introduced into the chamber, depending on the product. The flow, temperatureand humidity of the air have to be properly controlled in order to produce good dryingresults.Performance RequirementsTypical kiln temperatures range between 200 and 230F. While absolute estimates of theenergy 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 aproduct surface at a potential rate of roughly 22,000 Btu per square inch. Drying timesgenerally vary from 1 to 6 days. Longer drying times are required for wood that receivesoilborne or preservative treatments. Subjective anecdotal information indicates that theenergy 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. of12% or lower. Quality of the dried lumber product is unpredictable, unreliable and non-repeatable. Kiln operators should frequently monitor the kiln operation and should makeparameter adjustments as appropriate. Many years of experience would be required before anoperator is given charge of carrying out these tasks. Problems can arise due to unattendedoperationduringoff-hours.Thecommonpracticeofloweringthedesiredoperatingtemperatureduring off-hourswouldleadtoenergy inefficiency.Also,anunexpectedsituation may occur during the unattended period, and may lead to undesirable defects in thedrying boards. Furthermore, in view of the complexity, nonlinearity, and time-variant anddistributed nature of the drying process, the quality of the dried wood may not be uniformlysatisfactory in general. The fact that the drying results are unpredictable and that the entireprocess requires humans to close the control loop, provide an opportunity to use advancedtechnologies of sensing, actuation and control industrial kilns, with the goals of reducing theenergy consumption and improving the quality of dried product.About 65% of the $250 billion/year forest product sales is attributed to lumber andvarious wood products. Innovations in sensing, actuation, and control can result in significantreductions in energy usage in kilns. The study summarized here provides an indication of thetechnologies that are appropriate and the energy savings that are possible.

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SENSORS AND ACTUATORS10ConstraintsA conventional wood-drying kiln basically consists of electric coils for heating the air, whichis circulated by rows of fans along the upper deck of the kiln. The heated, dry air is directedthrough the stacked lumber by a plenum chamber. The water removed from the wood isturned into water vapor by evaporation, and the saturated air is then released through airvents. A conventional kiln operates in an open-loop manner based on a pre-specified dryingschedule. This process requires a full-time operator to frequently monitor and manuallyadjust all parameters according to the preset schedule. Due to the complex and distributednature of the wood drying process, the end product is usually unpredictable, unreliable andunrepeatable. 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. Insummary, 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 formodification 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 reducethe energy consumption; and are not monitored during unattended periods–possiblyresulting in product defects; e.g., splits or cracks.Kiln drying is an energy-intensive process. In addition to the energy that is used for thedrying process itself, some energy (electrical) is used for operating the fans in a kiln and forproduct repositioning during drying. The United States Department of Agriculture's ForestProduct Laboratory research indicates that drying operations more commonly burn woodwastes rather than fossil fuels for their energy source. Proper air circulation and optimumtemperature and residence schedules can result in significant reductions in kiln dryingenergy. In addition, Environmental concerns involve emissions from kilns, combustionsystems, and treating agents. Waste heat from kilns can be recovered by means of heatexchangers. Wood-drying kilns have been suggested as a candidate technology using ground-source heat pumps for supplemental energy. These observations indicate that wood dryingkilns provide a major opportunity for achieving significant benefits in energy efficiencythrough the use of advanced technology.SensorsConsider the prototype wood-drying kiln shown in Figure S1.16(a), which is a downscaledversionofaconventionalkilnthatisusedinindustry,andhasthedimensionsofapproximately943. The kiln has 12 thermocouples strategically positioned within it, tomeasure 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) tomeasure the air flow rate in the plenum; and 8 pairs of wood moisture content (MC) sensorsthat are nailed into the wood.ActuatorsThe prototype kiln is equipped with a pulse-width-modulated (PWM) filament heater and avariable speed fan as the actuators for heating and air circulation.

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