Slide 1OutlineReference listWeb referencesMajor applicationsBasic Working Principle PressureBasic Working Principle PressureSample Configuration 1Basic Working Principle StrainBasic Working Principle StrainSample Configuration 2Major SpecificationsMajor SpecificationsChoosing a sensorChoosing a sensorLimitationsRetailors and CostsVIBRATING WIRERoger C. [email protected] 5320 - MechatronicsAssignment #1OutlineReference listMajor applicationsWorking principleExample in fieldSpecificationsLimitationsWhere to findReference listCampbell Scientific Inc.Durham Geo Slope IndicatorGeokonGauge TechniqueRoctestWeb referenceshttp://www.slopeindicator.com/instruments/piezo-vw.htmlhttp://controls.engin.umich.edu/wiki/index.php/PressureSensorshttp://www.gage-technique.demon.co.uk/instruments/sg-intro.htmlhttp://www.canterbury.gov.uk/buildpage.php?id=705Major applicationsMonitoring water pressure in and out of a tank.Pore pressure monitoring on land fills and tailing dams.Structural monitoring of strain and/or load.Any other application that requires a monitoring of pressure, strain, load or water depth.Basic Working PrinciplePressureFigure from:http://www.canterbury.gov.uk/buildpage.php?id=705Basic Working PrinciplePressureBore holes are drilled into sensor to allow pressure into main chamber. Usually passing through a filter in order to rid the system of particles.Fluids or gases then push on the diaphramPressures on the diaphragm cause changes on the tension & frequency of the wire.Wire is excited by the electromagnetic coilsChanges in these parameters are then transmitted through the coils to a read out device or a datalogger to save measurement detailsSample Configuration 1Pressure in fluid tank•A vibrating wire piezometer is inserted into a tank.•Calibration is typically not required depending on model •Once inserted into tank a measurement is taken. Giving the user the pressure at the bottom of the tank.•Any changes in fluid level will result in a new measurement shown by the sensor.Basic Working PrincipleStrainFigure from:http://cee.engr.ucdavis.edu/faculty/chai/Research/Benicia%20Martinez/vibrating-wire-strain-gage.jpgBasic Working PrincipleStrainConnect across the axis of interest•Usually involves soldering of the sensor to the structureStrains to the load or structure will cause the resistive element inside the sensor to expand or contract.Measuring the total resistance of the element will tell the amount of strain the structure or load.Sample Configuration 2Strain•Solder sensor to desired axis of measurement on bridge•Connect sensor to a voltage source as well as a data logger to keep track of the measurements and data•When load is under stress and experiences a strain the sensor will interpret that with a change in resistance and thus a change in measurement will occur.Major SpecificationsPressure: different models range from 0 – 1000+ psi.Pressure accuracy: ±0.1% of full scale outputTemperature: Operating range -40o C to 230o CExtremes not available in a single modelResolution: 0.025%FSFilter: 50-micron sintered stainless steel•Some models also have ceramic filtersMass: anywhere from .10kg to 1.5kgMajor SpecificationsDiaphragm displacement: < .001 cm3Linearity: < 0.5% FSSensitivity: 1*10^5 MpaThermal Drift: < 0.1% F.S. / °CInput signal, sinusoidal: 150 to 170 mV rmsOutput signal, sinusoidal: 10 to 30 mV rmsChoosing a sensorWhat type of material is your vibrating wire senor going to be located in?Some environmental factors require the that sensor have a non-corrosive exteriorHigher pressure applications require a stronger exterior Sensor data must be transmitted to a source via a cable. Choosing the cable sheath is also important, different applications call for different requirements.Choosing a sensorHow are you going to extract the data given by the sensor?Handheld devices are available to read out the current dataData loggers are mini computers that are programmable and can be used to read, process, and save data from the vibrating wire sensors. These are typically used if you want to monitor a system for an extended period of time.LimitationsHigh rate of change in pressures (depending on make and model)Casing – different applications require different housingVarious models don’t come with a thermistor for temperature acquisition Cheaper models cover smaller pressure spectrum7.5 MPa is highest pressure I’ve foundThermal operating range – higher temps usually require more expensive modelsRetailors and CostsGeokon: $395 - ~$1300Gauge TechniqueRoctestSlope Indicator (VWP series):
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