17 Appendix
Page 6
17.2.Accuracyofthethermocouplemeasurements
Themeasurementinaccuraciesthereafteraregivenasmaximumvalues:typicalvaluesare2to3
timesless.
Themeasurementaccuracyintemperatureisthe sumofseveralpossiblesourcesofinaccuracy:
Pl:accuracyofstandardisation
Ps:coldweldaccuracy
Pm:accuracyofthemeasurementoftheequivalentvoltage
Pd:accuracyofthemeasurementoffsets
Thetotalaccuracyisthen:Pt=Pl+Ps+Pm+Pd
Fortherecorder:
Pl= 0.25 Cforallthethermocouples
Ps= 1.25 Cforallthethermocouples
Pd= 0.15%oftheoffset
Pm=giveninthetables
Measurementaccuracy:Pm
ThemeasurementaccuracyPmdependsonthevoltagerangeusedbytheappliance. The
measurementerrorindegreeswillthenbethemeasurementerrorinvoltagedividedbythe slopein
V/ Cofthethermocouple.Foreachthermocouple,anillustrativevalueofthe slopeisgivenata
giventemperature. This slopevalueisrelevantforthethermocoupleandallowsyoutocalculatethe
temperatureerror.Ifyouwanttohaveevenfurtheraccuracy,youhavetoreadthe slopeinthe
thermocouplereferencetables(becauseitchangeswiththetemperature).
EXAMPLEOFACCURACYCALCULATION
Ameasurementismadewiththerange50 Ccentredon25 CwithaJthermocouplewithoutcold
weldcompensation.
Pt=Pl+Ps+Pm+Pd
Pl= 0.25 C(accuracyofstandardisation)
Ps= 0 C(nocoldweldcompensation)
Pd= 0.04 C(+ 0.15%ofthetemperature,papermedium)
Pm= 0.20 C(extractedfromthetableatrange50 C)
Max.totalaccuracy:
Pt=0.25+0.04+0.20= 0.49 C