Tachometers – An OverviewTachometer, What’s That?What Are the Different Types of Tachometers?Comparison Between Analog and Digital TachometersDigital TachometersClassification Based on Data Acquisition TechniqueClassification Based on Measurement TechniqueComparison Between Contact and Non Contact TachometersComparison Between Time and Frequency Based MeasurementTypical Specifications of a Non Contact Type TachometerTypical Specifications of a Contact Type TachometerBlock Diagram of a Digital TachometerOptical SensingMagnetic SensingSignal ConditioningMicrocontrollerDisplay UnitAnalog TachometersSlide 19Analog Measurement TechniquesHow To Choose a Tachometer?CalibrationTachometers – An Tachometers – An OverviewOverviewAliasgar KutiyanawalaUtah State UniversityAliasgar Kutiyanawala 2Tachometer, What’s That?Tachometer is used for measuring rotational speedCan be used to measure speed of a rotating shaftCan also be used to measure flow of liquid by attaching a wheel with inclined vanesAliasgar Kutiyanawala 3What Are the Different Types of Tachometers?Tachometers can be classified on the basis of data acquisition – contact or non contact typesThey can also be classified on the basis of the measurement technique – time based or frequency based technique of measurementThey can also be classified as analog or digital typeAliasgar Kutiyanawala 4Comparison Between Analog and Digital TachometersAnalog TachometerHas a needle and dial type of interfaceNo provision for storage of readingsCannot compute average, deviation, etcDigital TachometerHas a LCD or LED readoutMemory is provided for storageCan perform statistical functions like averaging, etcAliasgar Kutiyanawala 5Digital TachometersAliasgar Kutiyanawala 6Classification Based on Data Acquisition TechniqueContact type – The wheel of the tachometer needs to be brought into contact with the rotating objectNon Contact type – The measurement can be made without having to attach the tachometer to the rotating objectAliasgar Kutiyanawala 7Classification Based on Measurement TechniqueTime Measurement – The tachometer calculates speed by measuring the time interval between the incoming pulsesFrequency Measurement – The tachometer calculates speed by measuring the frequency of the incoming pulsesAliasgar Kutiyanawala 8Comparison Between Contact and Non Contact TachometersContact TypeThe tachometer has to be in physical contact with the rotating shaftPreferred where the tachometer is generally fixed to the machineGenerally, optical encoder / magnetic sensor is attached to shaft of tachometerNon Contact TypeThe tachometer does not need to be in physical contact with the rotating shaftPreferred where the tachometer needs to be mobileGenerally, laser is used or an optical disk id attached to rotating shaft and read by a IR beam or laserAliasgar Kutiyanawala 9Comparison Between Time and Frequency Based MeasurementTime BasedThe tachometer calculates speed by measuring the time interval between pulsesMore accurate for low speed measurementTime to take a reading is dependant on the speed and increases with decrease in speedThe resolution of the tachometer is independent of the speed of the measurementFrequency basedThe tachometer calculates speed by measuring the frequency of pulsesMore accurate for high speed measurementTime to take a reading is independent of speed of rotationThe resolution of the tachometer depends on the speed of the rotating shaftAliasgar Kutiyanawala 10Typical Specifications of a Non Contact Type TachometerDisplay 5 digits large LCDRange: 2.5 - 99,999 RPMDistance: 50 to 1,000 mm; 12 to 40 inches.Resolution: 0.1 RPM<1000 RPM (2.5 toG 9,999 RPM)GGGGGGGGGGGGGGG 1.0RPM >1000 RPMMeasurement angle: at less than 120 degrees.Range selection: AutoLaser Output Power: <1mW class IISampling Time: 1.0 seconds (over 60 RPM)Memory: Last value, Max Value, Min. ValueTime base: Quartz crystalCircuit: Exclusive one-chip LSI circuitBattery: 4 X 1.5V AAWeight: 300g/0.65lbSize: 190 X 72 X 37 mmAliasgar Kutiyanawala 11Typical Specifications of a Contact Type TachometerDisplay 5-digit LCD DisplayRange selection Automatic range selectionTime Base 4MHz Quartz CrystalSampling Time 1 second (>60 rpm); >1 second (10 to 60 rpm)Accuracy ± (0.1% of reading + 2 digits)Photo Tachometer Distance 2 to 12” (5 to 30cm)Operating Temperature 32 to 122oF (0 to 50oC)Operating Humidity 80% RH Max.Power supply 9V BatteryBattery Life 40 hours (approx.)Applicable standards EN 50081-1/1992 (EN 55022) EN 50082-1/1997 (EN 55024)Dimensions 461700: 4.9 x 2.0 x 1.3” (124 x 51 x 33mm)Weight 461700: 4.0 oz. (114g)Aliasgar Kutiyanawala 12Block Diagram of a Digital TachometerOptical / Magnetic SensorSignal ConditioningMicrocontrollerMemoryDisplayExternalPort (to controller)Aliasgar Kutiyanawala 13Optical SensingIt is used to generate pulses proportional to the speed of the rotating shaftCan be achieved by the following ways:Attaching a disk, which has an alternate black and white pattern, to the shaft and reading the pulses by a IR module pointed towards itUsing a slotted disk and a U shaped IR emitter detector pair to generate waveformsAliasgar Kutiyanawala 14Magnetic SensingHall effect sensors – These make use of the Hall effect to generate pulses proportional to the speed of the shaftPassive magnetic sensors – These make use of variable reluctance to generate pulsesAliasgar Kutiyanawala 15Signal ConditioningThe output of the sensors may be noisyThe output may have to be amplifiedIt has to be digitized. This is done by Schmitt triggering so as to bring voltage to TTL levelsAliasgar Kutiyanawala 16MicrocontrollerNot essential, but is generally the norm to have a microcontrollerCompute the speedCan store the readingsCan output values to a display unitGive out warning signal when speed reduces / increases beyond set marginsTransfer data to external controllerAliasgar Kutiyanawala 17Display UnitUsed to output the values to the operatorCan be used to view the stored valuesAliasgar Kutiyanawala 18Analog TachometersAliasgar Kutiyanawala 19Analog TachometersThese are generally the ones that display the speed of your carThe interface is needle and dial arrangementAliasgar Kutiyanawala 20Analog Measurement
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