Instrumentation Lab. Experiment#1 calibration (report)
- 1. Jordan University of Science and Technology Faculty of Engineering Department of Mechanical Engineering Instrumentation and Dynamic Systems Lab Experiment #1: Calibration
- 2. Introduction: Instrumentsystemscanbe classifiedmainlyinto Mechanical andElectrical systems.The formerisrarelyused,simple,andlessaccurate whilethe latteriswidelyused,more accurate and give digital outputsignals.These instrumentsare probable tohave errorsor become lessaccurate as a resultof continuoususage whichcausesthe partsto wearor be fatigued,thustheymustbe periodicallycheckedandfixedtokeepwithinan acceptedrange and to inhibiterroraccumulation. Zero-offset,range errorandreadingdeviationare three commonerrors thatoccur to instrumentdevices,calibrationisamajor processtotake care of these typesof errors.It’sa processof comparingthe readingsof a specificinstrument witheitherastandardor a more accurate device. Inthisexperimentthree differentsystems are calibratednamely;negativepressure,deadweighttesterandvoltmetersystems. Hysteresisphenomenonisthe deviationinreadingswhenmeasurementsare taken increasinglyandthendecreasingly,itshouldbe givenagreatimportance because many explanationscanbe executedusingthisphenomenon,suchasthe lossof energyinthe magneticcurve. Equipments and instruments: 1- Negative Pressure System: A vacuumcompressorlike the one usedina refrigeratorisusedandis attachedto a mercury manometerbya valve to control the vacuum pressure,apressure gage ismountedonthe valve suctionto measure the negative pressure value and compare itsreadings withthe manometersoitcan be calibrated. 2- Dead weighttester system: In thissystemapistonisconfinedinsidea chamberfilledof oil andconnectedtoa pressure gage tomeasure the oil pressure inside. Accuratelymeasuredweights are put above the pistontoapplya pressure inside the oil whichismeasuredbythe gage.The two valuesare comparedandthe pressure gage is calibrated. 3- Voltmeter: Analogmeters(mechanical) anddigital meters (electrical)are usedtomeasure bothDC andAC signalsbutwithlattertype being more accurate, soa multimeterisusedtocalibrate ananalogmeter.A DC power supplyisusedto give a DC signal while the ACsignal isgeneratedusingafunction generator.
- 3. AC FunctionGenerator DC PowerSupply Data Analysis: 1- Negative Pressure Table 1: Actual and gage readings of the mercury level in the manometer versus the corresponding gage level increasingly. Table 2: Actual and gage readings of the mercury level in the manometer versus the corresponding gage level decreasingly. 2- Dead Weight (Positive Pressure) 0 5 10 15 20 25 30 35 0 10 20 30 40 GagePressure(cm) Manometer Pressure (cm) Figure 1: Hysteresis in Negative Pressure System Incrasingly Decreasingly Actual Manometer (cm) Gage reading(cm) Pressure Gage Actual Manometer (cm) Gage reading Pressure Gage (cm) 3 4 30 31 6 7 27 28 9 10 24 25 12 14 21 23 15 16 18 19 18 20 15 16 21 23 12 14 24 26 9 9 27 28 6 4 30 31 3 1 Actual Weights (psi) Gage Dial (psi) Actual Weights (psi) Gage Dial (psi) 20 22 200 181 40 37 180 172 60 55 160 155
- 4. 0 20 40 60 80 100 120 140 160 180 200 0 50 100 150 200 250 GageDial(psi) Actual Weight (psi) Figure 2: Hysteresis in Positive Pressure System Decreasingly Increasingly 80 73 140 132 100 90 120 112 120 112 100 95 140 131 80 72 160 150 60 58 180 172 40 40 200 181 20 22 Table 3: Actual and gage pressure readings of the dead weight instrument increasingly. Table 4: Actual and gage pressure readings of the dead weight instrument decreasingly 3- Voltmeter DC Scale Actual Digital (volt) Gage Analog (volt) 1 0.95 2 1.93 3 2.92 4 3.90 5 4.93 6 5.96 7 6.91 8 7.91 9 8.99 10 9.94 Table 5: Actual and gage readings of the DC analog & digital meter increasingly. Error = | 𝐴𝑐𝑡𝑢𝑎𝑙 −𝐴𝑝𝑝𝑟𝑜𝑥𝑖𝑚𝑎𝑡𝑒 𝐴𝑐𝑡𝑢𝑎𝑙 | ∗
- 5. 100% = | 4−3.9 4 | ∗ 100% = 2.5% AC Scale: Actual Digital (volt) Gage Analog (volt) 1 0.89 2 1.84 3 2.79 4 3.84 5 4.83 6 5.85 7 6.87 8 7.8 9 ــــــ 10 ــــــ Table 6: Actual and gage readings of the DC analog & digital meters decreasingly. Error = | 𝐴𝑐𝑡𝑢𝑎𝑙 −𝐴𝑝𝑝𝑟𝑜𝑥𝑖𝑚𝑎𝑡𝑒 𝐴𝑐𝑡𝑢𝑎𝑙 | ∗ 100% = | 3−2.79 3 | ∗ 100% = 7%
- 6. Discussionof Results: 1- Negative Pressure System: Tables1 and 2 showthat there are differencesbetweenthe valuesof vacuumpressure measuredbythe gage and the manometer.The gage resultsina large percentage errorat low pressure valuesanditfallsasthe vacuumpressure isincreased.Thusthe pressure gage should be calibratedtogive more accurate data. Hysteresisiswell illustratedinfigure 1,whichshowsthatthe two loadingcurvesaren’tmatched completely.Thisphenomenonshouldbe studiedcarefullybecausemanyexplanationscanbe executeduponit. 2- Positive Pressure System(Dead WeightTester): Comparingthe measuredvaluesbythe pressure gage withthe weightsshowsthatthere are deviationsinthe gage readingsthanthe actual values asshownintables3 and 4 . The gage needstobe calibratedbecause the errorvaluesare highandreaches10% percentage error. As previouslynoticedinthe firstpart,bychangingthe loadingscheme hysteresisisrecordedas illustratedinfigure2. 3- Voltmeter: Tables5 and 6 showsthe measuredvoltage difference bythe analogvoltmetercomparedtothe digital meter.The analogmeterhasa zero-offsetandneedtobe calibratedalso.Itproduces largererrors whenACsignals are measuredreachingapercentage errorvalue of 7% whichisn’t acceptedforengineeringpurposes,thusitshouldbe fixedorreplaced. Conclusions: 1- Calibration could be performed by either a standard device or a more accurate one. 2- Hysteresis is an important phenomenon that an engineer should study carefully and use it in making explinations. 3- The pressure gages in parts 1 and 2 should be calibrated. 4- The analog ammeter in part 3 should be fixed or replaced.