Executive Summary - Computer Action Team



FSAE FLOW TESTING DEVICEPROGRESS REPORTWINTER 2012Group MembersAdam BarkaJasper WongKeith LundquistLong DangVu NguyenPortland State University AdvisorDr. Chien WernIndustry AdvisorEvan WaymireExecutive SummaryViking Motorsports (VMS) is a student organization at Portland State University that participates in the Formula SAE student competition. To be more competitive, VMS commissioned the PSU capstone team to design and manufacture a device to determine the flow coefficients of their custom powertrain components by June 2012. Viking Motorsports has defined a series of product design specifications outlining the device’s capacity, reliability, and cost; the device will be able to test components from 10 to 250 cfm at a test pressure of 28 inches of water channel, be able to archive 95% repeatability, and will cost less than $3,500.The capstone team performed an external search focusing on competing devices, as well as on technologies that could be used in a flow testing device. The team conducted an internal search using the external search findings and design specifications, and thereby outlined three possible designs. A concept evaluation revealed the best option to be the balanced design. The capstone team is currently performing detailed design on this concept. Further design, manufacturing, and testing will be completed next term.ContentsIntroduction and Background1Mission Statement2Project Plan2Product Design Specification3External Search4Internal Search5Concept Evaluation and Selection7Detailed Design Progress9Conclusion12AppendicesIntroduction and BackgroundEach year, the Society of Automotive Engineers (SAE) invites colleges from around the world to participate in their Formula SAE series competition. This competition challenges students from each school to design, build, and race an open-wheeled formula style race car. Portland State is represented in this series by the Viking Motorsports (VMS) student group.In order to encourage teams to focus on design and optimization rather than on generating raw power, the SAE has imposed a series of regulations on the powertrain subsystem of the race car. The most notable regulation is that all of the air supplied to the car’s engine must go through a 20 mm restrictor, which severely limits the output power of the engine. To overcome this, VMS must be able to accurately measure the mass flow of any customized component (see Appendix A) at a standard pressure in order to determine parasitic losses to the engine. In addition, the team must measure the ratio of the theoretical volume flow to the actual volume flow through the piece, called the flow coefficient, of the cylinder intake and exhaust valves, as well as of the butterfly valve on the throttle. These values are necessary for the team to utilize 1-D simulation software to improve their design. Currently, VMS has no method to test for these values.In order to flow test their components, the powertrain group could purchase a device known as a flow bench. A typical flow bench uses a pump to move air through a device under test (DUT) and then through a calibrated obstruction flow meter at a standard test pressure, which is measured upstream of the flow meter. The pressure drop across the obstruction is a known function of the volume flow rate through the meter. The mass flow rate through the DUT is calculated from the volume flow across the meter and from temperature/pressure measurements at the DUT. Fig. 1 shows a typical flow bench operating under a negative pressure differential (relative to atmospheric). A flow bench would reverse the flow by creating a positive pressure differential relative to atmospheric.Figure SEQ Figure \* ARABIC 1. Simple flow bench. P1 is the test pressure; the difference P2-P1 is measured to produce mass flow rate.There are many flow benches available for purchase, but all share similar limitations. Foremost is cost. Commercial flow benches with enough air flow capacity to accurately test VMS powertrain components cost anywhere from $5,000 to $15,000. In addition, commercial devices would require VMS to build customized mounts to accommodate the restrictor, intake manifold, and exhaust. Finally, commercial flow benches do not easily allow for future improvements or modifications. VMS has constantly changing needs, and so must be able to modify the flow bench. The other option is to buy a home build kit. These “do it yourself” (DIY) kits include key components and/or detailed plans with which to build a flow bench. The kit is a more affordable option. However, the measurements provided by flow benches built from DIY kits have unspecified uncertainty. In addition, they generally require manual calculation to attain the flow rate, which leads to more time needed to complete an experiment. Finally, DIY options would also need customized test fixtures to mount all components.Mission StatementThis team is challenged to design and build a device capable of measuring the flow coefficients for the intake, exhaust, and throttle valves of a formula SAE racecar at various open positions, and to measure the mass flow through the racecar’s intake manifold and exhaust ductwork. The device will measure these values at a standard test pressure of 28 inH20 with 95% measurement repeatability. The completed project, consisting of a working prototype, testing results, detailed drawings, bill of material, and detailed reports, will be presented in June 2012. If successful, the project would help the VMS team to validate and improve their designs.Project PlanTo meet the completion deadline of June 2012 and other progressive deadlines, the team created a detailed Gantt chart (Figure 2). The chart lists all deadlines that are required for the completion of the project. The main tasks that have been completed to date include creating the product design specifications, conducting the external/internal search, and performing concept evaluation. The system-level design is currently in progress, and will be completed at the beginning of the 2012 Spring term. After creating the system level design, the team will complete parametric design and begin the manufacturing and testing process. The project plan is subject to change.Figure SEQ Figure \* ARABIC 2. Detailed Gantt chart.Product Design SpecificationsProduct design specifications (PDS) define the customer’s needs in terms of engineering metrics and criteria. The team has verified its progress throughout the design process using the PDS provided by VMS. As the design evolved, some targets and metrics were re-evaluated to provide the best representation of the customer’s needs. Appendix B includes a detailed list of these requirements. VMS highlighted the following criteria as the most significantThe device must be able to pull and push 10 to 250 cfm of air at a test pressure of 28 inH20.Experimental results must be repeatable within 95%.The device must include a detailed user manual. The device footprint must be no larger than 6 ft x 4 ft.All parts must be easy to inspect and replace. A maintainence schedule must be provided for all replaceable parts.The device must cost less than $3,500.External SearchIn order to gain information on existing technologies relating to the design of the flow testing device, the team conducted a detailed external search. This search investigated direct competing products and technologies that could be utilized. Fig. 3 illustrates two direct competitors: the Flow Performance Basic 2.0 and the SF-450 made by SuperFlow. The Flow Performance Basic is a DIY solution used commonly by hobbyist tuners. It is a small and portable but low capacity product. The SF-450 is a commercial flow bench aimed at the professional race engine tuner. It has high capacity, accuracy, and repeatability, but is expensive. Table 1 summarizes main specifications of the two products. b. Figure SEQ Figure \* ARABIC 3. Available market flow benches: (a) Flow Performance Basic 2.0 and (b) SF-450(Images courtesy of Flow Performance LLC and SuperFlow) Table SEQ Table \* ARABIC 1. Specification of similar productsSystemsFlow Performance Basic 2.0SF-450Capacity210 cfm at 10 inH2O450 cfm at 40 inH20ReliabilityUnknownHighDAQDigitalAnalog and DigitalFlow ControlManual ControlAutomatic ControlAir SourceShop VacuumCentrifugal Air PumpFlow MeterOrifice PlateOrifice Plate, Velocity ProbeCost~$2,000~$7,000In addition to competing products, the team included relevant technology including patents in our search (Appendix C).? These included flow bench setups, flow stabilizers and laminar flow element style devices.Internal Search32004001567815The air flow testing device is best described as a combination of three key subsystems: 1) the flow metering device, 2) the air source and flow control devices, and 3) the data acquisition (DAQ) system. Initial brainstorming focused on determining the range of options for each of these systems, as detailed in Appendix D. Additional brainstorming sessions focused on creating three different design concepts with progressively greater functionality and cost. Table 2 summarizes the advantages and disadvantages of designs 1, 2, and 3. Design 1: The basic design (Figure 4) meets the meets the PDS cost and functionality requirements as simply and inexpensively as possible. Single orifice plate meter Analog pressure and temperature measurement devicesPVC ductworkInexpensive shop vacuum and a manual restriction valveNo flow alternator296227514605Figure SEQ Figure \* ARABIC 4. Schematic of Design 1 executing intake testing.00Figure SEQ Figure \* ARABIC 4. Schematic of Design 1 executing intake testing.Design 2: The balanced design (Figure 5) meets the PDS cost and functionality requirements with the addition of fast measurement turnover. Multiple orifices plate meters Large settling chambers before/after flow meter with laminar gridDigital temperature and pressure measurement devicesHigh pressure centrifugal air pump (single or multiple in parallel/series)Manually controlled flow diverterFlow alternator (not shown in Figure 5)Figure SEQ Figure \* ARABIC 5. Schematic of Design 2 executing intake testing.Design 3: The ideal design (Figure 6) meets the cost and functionality requirements with the addition of fast measurement turnover and high accuracy.Hot wire anemometerDigital temperature and pressure measurement devices High pressure centrifugal air pump (single or multiple in parallel/series)Fully automated flow controlFlow alternator (not shown in Figure 6)Figure SEQ Figure \* ARABIC 6. Schematic of Design 3 executing intake testing.Table SEQ Table \* ARABIC 2. Advantages and disadvantages of the three design concepts.DesignAdvantagesDisadvantagesDesign 1InexpensiveSimple set-upEasy to manufacture and maintainSmall footprintLow repeatabilitySlow measurement turnover timeNarrow operating rangeManual data analysisDesign 2High repeatabilityEasy to maintainAutomatic data analysisMedium operating rangeLarge system lossesDesign 3High repeatabilityLarge operating rangeFast measurement turnoverAutomatic data analysisExpensiveLonger set-up time between experimentsHard to maintainConcept Evaluation and SelectionThe goal of the concept evaluation is to determine the best possible design in an unbiased and technical way. The team achieved this by using a weighted concept scoring matrix. The team first took the key PDS requirements selected by VMS and assigned them importance scores from 1 to 3. These scores indicate the extent to which VMS desires the design to exceed the minimum requirements. The following list describes the importance scores of the requirements and the basis factors that impact them.Cost Importance: 1.5 A cost lower than PDS requirements would be beneficial to VMS, but is not essential. Therefore, cost is of medium low importance.Basis: Initial cost of the flow element, DAQ, flow system, and also maintenance costs.RepeatabilityImportance: 3Because the flow testing device is a measurement device, repeatability is very important. Basis: Relative uncertainty of the metering element, resolution of the DAQ, and level of control over the air flow.MaintenanceImportance: 1VMS would like the least amount of required maintenance possible. However, this is not as important as the functionality of the device.Basis: Replacement frequency and accessibility of key components.Turnaround TimeImportance: 3Turnaround time is of high importance, because a higher turnaround time would allow for more experimental treatments, resulting in more accurate data. Basis: Quickness of measurements during a single experiment, the time the device takes to reach a steady state value, and how long it takes to reverse the flow. Does not include time needed to set up the experiment.Ease of UseImportance: 1.5It is important that the device is easy to use and take measurements, however it is more important that the device can make repeatable and fast measurements.Basis: Amount of training required, ease of taking measurements, digital or analog readout, the need to adjust the device between experiments, and the need for manual calculations are all taken into account in this section.The team used the SuperFlow 450 and the PDS cost requirement as baselines to compare the three designs. The team gave each design a value from 1 to 5. A value of 1 represents a design with significantly worse functionality than the baseline, and a value of 5 represents a design that meets or exceeds the baseline. Table 3 is the resultant concept scoring matrix. Table SEQ Table \* ARABIC 3. Concept scoring matrix for Designs 1, 2, and 3. Designs are scored from 1 (worst) to 5 (best) compared to the baselines. Scores are multiplied by the requirement’s importance and summed to create their total points.RequirementImportanceDesign 1Design 2Design 3Cost1.5531Reliability3255Maintenance1552Turnaround Time3145Ease of Use1.5134Weighted score23*41*39.5**50 points possibleDesign 2 is the highest scoring design, and therefore was selected as the final top level design concept. During this process, however, it was determined that a majority of the points for Design 3 came from the automated function. The team intends to include this function in their final design, since the flow diverter can cheaply and easily be converted to an automated system. In addition, the team decided to include the analog measurement devices from Design 1 to provide a check for the digital devices and allow use of the device if the software is not functioning.Detailed Design ProgressThe team created a top-level design based on the evaluation of the concept design matrix and PDS criteria. The system will incorporate an orifice plate for the flow element, parallel centrifugal pumps with an automated flow diverter for the flow control, and a digital measurement system with additional analog manometers (Figure 7). This section describes the design at the subsystem level. When the system level design is complete, the team will begin the detailed parametric design. Figure SEQ Figure \* ARABIC 7. Detailed schematic of the top-level design executing “intake testing.” Pressure/temperature sensors, the laminar flow grid, and pressure manometers are not included. The chosen design utilizes an orifice plate metering element. According to ASME G00079 the accuracy of an orifice meter is within 2 to 4% for a range of flow rates of 4 to 1. Since the required flow rate range is 25 to 1, at least 6 sizes of orifices will be necessary. Therefore, the team will use a plate that houses multiple orifice sizes. Rubber plugs will seal orifices that are not in use. The number and size of the orifices depend on the parametric analysis of the system. Pressure transducers will measure the differential pressure between two large plenums, which are separated by the orifice. These sensors will measure the system loss of the orifice plate. Because the pressure loss is a function of volume flow rate, the mass flow rate or flow coefficient through the DUT can be calculated. In addition, these plenums will stabilize the pressure measurements. The design concept for the flow control subsystem consists of high pressure vacuum pumps in parallel, which are regulated by an automated flow diverter. The flow will be reversed using a flow alternator. The centrifugal vacuum motors are placed in a parallel configuration to increase the total volume flow of the system, while sustaining the pressure differential required. The pump must also overcome the minor losses in the ductwork and the pressure drop of the orifice plate, so a parametric analysis of the system is necessary to determine the number of pumps and the total pressure head required. Bi-directional flow is achieved with the flow alternator depicted in Fig. 8. This design uses a rotating baffle to change the direction of flow so that the operator need not disconnect any ductwork. The flow alternator is optimized for creating a negative pressure differential, which is appropriate for a majority of tests.43211751457325B00B13208001518920A00A -2807970177165A00AFigure SEQ Figure \* ARABIC 8. Air box with flow alternator creating a negative pressure differential (A) and a positive pressure differential (B).The device maintains a test pressure of 28 inH20 by adjusting the flow rate through the orifice. This control will come from a flow diverter. The pumps will therefore be able to maintain a constant net positive suction head and efficiency throughout the testing range, which will increase the life of the pumps. The flow diverter will be controlled by an actuator which connects to the DAQ system, which will automatically adjust the flow until the desired test pressure is reached. Digital data acquisition will be used to record pressure and temperature measurements, to regulate the flow diverter, and to perform automated conversions from pressure differential to mass flow rate or flow coefficient. The test pressure will be measured by a single pressure transducer; the DAQ will use the test pressure to automatically calculate the air density and control the flow diverter via analog output. A bi-directional differential pressure transducer will measure the pressure difference across the orifice plate. A thermistor will provide temperature measurements to automatically correct the density calculations for the current ambient temperature. A u-tube manometer, an inclined manometer, and a thermometer will accompany the test pressure transducer, the pressure differential transducer, and the thermistor. These will ensure that all automated systems have a manual backup. Detailed parametric design of the DAQ subsystem will begin after the detailed analysis of the other two subsystems.ConclusionThe team has completed the Product Design Specification, external/internal search, concept evaluation, and finalized the main components of the system-level design. The flow testing device will use an orifice plate as the flow metering element as it is easy and cheap to manufacture. Digital acquisition will be used for automated and accurate data recording, with analog manometers as fallback and for reference. Multiple parallel centrifugal motors will be used to achieve the airflow and differential pressure required to test the required VMS componentsThe next step is for the team to begin parametric design of the subsystems. Due to time restraints and task prioritization, the team will shift the schedule to include Spring break in the project plan. Parametric design is slated to be completed at the end of March.At this point the team has 2 major concerns in the design of the flow bench. The first concern is the noise of the fans used in the flow bench, which will likely exceed the projected noise levels. Attempts will be made for noise reduction by securely mounting the motors with rubber gaskets on the plenum, and constructing the plenum with sound deadening material. At this time, noise level advisory, provided ear muffs, and after-hours operation are the solutions to this problem. The second concern is the mounting of component onto the flow bench. The team will be able to manufacture a mount for the heads, as it is a standard part for VMS. For further development however, the team will have to provide the dimensions for mounting so that VMS will be able to manufacture their own mounts.AppendicesAppendix A: 2011 VMS powertrain componentsThis section includes the components which VMS needs to test for mass flow rate, or flow coefficient. The kind of information needed and the specific mounting requirements of each component are detailed.A1. Intake ManifoldThis is the device which disperses the air which comes through the restrictor to the individual cylinders. The mass flow rate through each runner is needed to determine if all 4 cylinders are receiving the same amount of air. A custom test fixture needs to include a bracket with all four 25 mm, with three plugs. Flow only needs to me measured at a negative pressure differentail.Figure A1. Intake manifoldA2. Throttle/RestrictorThis piece contains both the throttle butterfly valve and so VMS needs flow coeficients for the valve, and mass flow at wide open throttle. The custom test fixture would need a 25 mm adapotor with properly placed holes for the bolts, as well as a mechanism for controling the degree of opeing in the throttle valve. Flow only needs to me measured at a negative pressure differentail.Figure A2. Throttle bodyA3. ExhaustAfter combustion, the air in the engine is expelled to the atmosphere through the exhaust. VMS needs to know the pressure loss in this ductwork. The exaust will be mounted in a similar fashion to the intake manafold. This part needs a positive pressure differential. Figure A3. Exhaust systemA4. Cylinder HeadThe cylinder head contains the valves which regulate the intake and exhaust flow through each cylinder. Reliable flow confinements are needed for each valve for 1-D engine simulation software. The head needs a custom 67 mm bore adaptor and a device for controlling the valve lift. The cylinder head needs to be measured under both negative and positive pressure differential.Figure A4. Engine head (Honda CBR 600cc F4i)Appendix B: Detailed Product Design Specification This section contains the product design specifications in their full and updated form. Most importantly, the capacity, size, and the verification methods have been updated to better reflect the customer’s priorities.Table B1. Main requirements from the Product Design SpecificationsPriorityRequirementCustomerMetricTargetTarget BasisVerificationPerformanceRepeatability of measure flowVMS% error(+/-) 5Customer feedbackTestingCapacityVMScfm at inH2O≥250 at 28Group decision TestingTest intake, throttle, muffler, valvesVMSYes/NoYesCustomer feedbackDesignSafetyEmergency stopVMSYes/NoYesCustomer feedbackTestingWarning labelsVMSYes/NoYesCustomer feedbackDesignEgonomics safetyVMSYes/NoYesCustomer feedbackTestingEnvironmentLow noiseVMSdBA95Customer feedbackDesignErgonomicsNumber of operatorsVMSpeople1Customer feedbackTestingTraining time VMShours5Group decisionTestingSize and WeightFoot printVMSfeet6 x 4Customer feedbackDesignMaintenanceEasy to inspect and replace partsVMSYes/NoYesCustomer feedbackDesignFrequency of required maintenanceVMSmonths6Customer feedbackDesignInstallationTime to set upVMSmin20Customer feedbackTestingRequired specialized power sourceVMSYes/NoNoCustomer feedbackDesignCostTotal costPSUUSD3500Customer feedbackBill of materialsDocumentationPDSPSUDeadline01/30/2012Course requirementReceiptProgress reportPSUDeadline03/05/2012Course requirementReceiptFinal reportPSUDeadline05/28/2012Course requirementReceiptInstructionVMSYes/NoYesCustomer feedbackHard copyApplicable codes and standardsMeet industry standardsVMSYes/NoYesCustomer feedbackStudy of regulationsMaterialReasonable priceTeamYes/NoYesCustomer feedbackBill of materialLife in serviceContinued operation with approriate mainternaceVMSyears5Customer feedbackDesignManufacturing facilityDesign parts for manufacturabilityTeamYes/NoYesGroup decisionDesignAppendix C: External Search DocumentIn this appendix, the summary of the external search is reported. This is a list of related patents and technologies that we found.C.1 Flow Bench (US patent 4213327)This invention relates to apparatus for measuring the rate of air flow through a laminated panel. A flow bench is in the form of a vacuum box having a plurality of anvils on its top against which the material to be tested is placed.Figure C1. Side view of the flow bench associated with a pressure source and a pressure sensing system (US patent No. 4213327)C.2 Flow Stabilizer for Flow Bench (US patent 7024929)Since the flow through the component is subsonic, a flow stabilizing member placed downstream of the component can have an effect on the flow conditions in the component being test. In one embodiment, the flow stabilizing member provides more consistent results during the testing of the componentFigure C2. Side elevation view of an apparatus (US patent No. 7024929)C.3: Airflow bench with laminar flow element (US patent 7992454)A laminar flow system includes a laminar flow element (LFE) in sealed fluid communication with the air collection box at the outlet end. A blower is in sealed fluid communication with an outlet of LFE for generating airflow into the air collection box through a unit under test at the air inlet port and out of the air collection box through the laminar flow elementFigure C3. Schematic diagram of a testing system (US patent No.7992454)Figure C4. A perspective view of the internal structure of an example of a commercially available type of LFEAppendix D: Internal Search DocumentThis appendix is the detailed information of the sub-components of the flow deviceIt is clear from the external search that any device we design will have to include three major subsystems. These are the flow metering element, the air source, and the data acquisition system and so each these three subsystems were assed individually. D.1 Flow metering elementThe first subsystem is the metering element. This is the element which will evaluate the mass or volume flow rate of air through the DUT. The orifice plate meter, the hot wire meter, and the laminar flow element meter are the best options for the testing device.857264004310The Orifice plate meter was chosen for Designs 1 and 2 because of the low cost and the stability of measurements. Design 3 utilizes the hot wire because of the large operating range and accuracy.020000The Orifice plate meter was chosen for Designs 1 and 2 because of the low cost and the stability of measurements. Design 3 utilizes the hot wire because of the large operating range and accuracy.Table D1. Comparison of the top four flow meter choices.Flow MeterAdvantagesDisadvantagesHot Wire AnemometerLow number of pressure/temperature sensors needed.Low system losses.Accurate for a wide range of flows.Unidirectional measurements only.Large amounts of noise.Mounting issues.Orifice Plate MeterInexpensive.Easy to manufacture and replace.Measurements are stable (little noise).Large system losses.Low operating range.Edges wear down.Laminar Flow ElementVery accurate.Low system losses.Large operating range.Very expensive.Fouling/Clogging.Venturi MeterLow system losses.Accurate.Unidirectional measurements only.Expensive.Operating Range.D.2 Air sourceThe second subsystem is the Air source. There are 3 different types of pumps that we intended to use: the Axial Fan, the Centrifugal Blower, and the Vacuum Motor Figure D1. The Flow control system: Axial Fan, Centrifugal Blower, Vacuum MotorTable D2. Advantages and disadvantages of different type of air sourcesAir source AdvantagesDisadvantagesAxial FanSmallInexpensive $75Only able to measure at Low PressureLow volume 124 cfmCentrifugal BlowerHigh pressureHigh volume 2000 cfmLarge footprintUsing enormous powerToo expensive <$2000Vacuum MotorSmallInexpensive $99Less airflow than centrifugal Fan 150cfmAxial fans are designed for high cfm flow at low pressures. For the needs of the flow bench, the axial fan was not a suitable option for our air source needs. Besides, the centrifugal blower is not a suitable air source even though the centrifugal blower is designed for high cfm flow at high pressures. Their design specific are beyond the needs for the flow bench system and is too expensive for our budget. From this the vacuum motor is the simplest solution, and therefore was used in Designs 1, 2, and 3.D.3 Data Acquisition systemThe third subsystem is the DAQ. There is a large selection of DAQ’s on the market, and 3 different types were considered; Internal, external, and a stand-alone solution.Figure D2. DAQ’s, left to right; AD Link (Internal), National Instruments (External), Data Logger (Stand-alone)Table D3. Advantages and disadvantages of DAQ systemsDAQ AdvantagesDisadvantagesAD LinkUsing MATLAB easy to useLarge amount of channels: 16Inexpensive $600Must be built into PCData LoggerStand-alone deviceHigh accurateLack of channels: 8Expensive $1000Using HOBO wareNational InstrumentLarge amount of channels: 16Using LabviewCheap $500The National Instruments DAQ was chosen due to lower cost, adaptability to either desktop or laptop solutions though the USB connection, and native support of LabVIEW. The DAQ is also reasonably small, and does not require additional components to connect the pressure, temperature and flow sensors. Data is also handled easier since it is immediately available to the user on the computer. The flow diverter will be adjusted by a digital to analog converter, side-stepping the need for a built-in analog output signal and extra cost.D.4 Pressure transducersThere are 4 types of pressure transducers; Gauge, absolute, differential, and vacuum. These sensors greatly vary in size, pressure capacity, tolerance, and can have chemical and/or dust treatment as well.Table D SEQ Table \* ARABIC 4. Advantages and disadvantages of pressure transducersPressure sensorsAdvantagesDisadvantagesGaugeEasy to read valueAtmospheric pressure has to be accounted for.Two sensors are needed for differential pressure.AbsoluteDirect measurement of pressureAtmospheric pressure is includedGage pressure requires some work to calculate.Two sensors are needed for differential pressure.DifferentialAtmospheric pressure is not needed. Direct measurement between two chambers.Unidirectional measurement onlyCompounding failure pointVacuumSub atmospheric pressure measurement.Only measures negative pressure.BidirectionalPressure chambers can switch between high and low pressure.Atmospheric pressure is not needed.Direct measurement between two pounding failure pointFor convenience, a bidirectional pressure sensor will be used to measure the difference between upper and lower chambers. The sensor will omit the need for atmospheric pressure, as the sensor is a differential type. Differential pressure transducers specify high and low pressure zones, and the connections have to be switched to measure reverse flow. High pressure on the low pressure side can damage the pressure transducer, especially on transducers with low burst pressure. The bidirectional sensor will avoid this, and it will also remove the need to switch the connections. The third pressure transistor used to insure testing pressure will be an absolute pressure transistor.D.5 Temperature transducersThere are 3 types of temperature measuring transducers; Thermocouples, thermistors, and resistance temperature detectors (RTD). Thermocouples are 2 dissimilar metals that create a voltage drop with temperature change. Thermistors are thermal resistors that decrease in resistance as temperature increases. RTD’s increase in resistance as temperature increases.a b c Figure SEQ Figure \* ARABIC 93. Temperature transducer(a) Omega ON-960 thermistor. (b) Omega RTD-880. (c) Omega HSTC Series sealed thermocouple.(Images courtesy of )Table D SEQ Table \* ARABIC 5. Temperature sensorsTypePart name*Specification**Cost***ThermocouplesOmega HSTC Series250 oC maxFast response timeReference junction dependent$25ThermistorsOmega ON-9600 to 70 0.2 oCFast response timeEasy to install$44RTDOmega RTD-880-70 to 500 0.385 oCSlow response timeEasy to installBridge circuit dependent$49*, **, and ***: Part name, specification, and cost were taken from The thermistor type temperature transducer was chosen as it fits the needs the best. It is also simpler to setup by using an equation to calculate measured temperature, instead of using tabulated values or a 2nd reference transducer as for thermocouples. In the case of the ON-960, it is also a probe that is mountable to the housing. ................
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