User guide

4
IM 11M06D03-01E-A
I. INTRODUCTION
TherearetwotypesofsinglechannelcalibrationunitsofferedbyYokogawa.Thesecalibrationunitsareusedwith
the ZR402G Single Channel Oxygen Analyzer, to perform calibration of either ZR22G or ZO21D (obsolete) Oxygen
Probes.
TheAC1AutomaticCalibrationUnitutilizeselectricalsolenoidsthatarewiredtoandactuatedbytheZR402G.Once
activatedbytheZR402G,thecalibrationgasesowtotheZR22withouttheuseropeningvalvesoradjustingow
rates.TheMC1ManualCalibrationUnitisnotelectronicallycontrolledbytheZR402G.Duringcalibrationmode,the
usermustopenvalvesandadjusttheowratesofthecalibrationgases.BoththeMC1andtheAC1provideasingle
point of control for the calibration system.
II. OVERVIEW
2.1 CALIBRATION PRINCIPLES
ThissectionsetsforththeprinciplesofmeasurementwithaZirconiaoxygenanalyzerbeforedetailingcalibration.
Asolidelectrolyte,suchasZirconia,allowstheconductivityofoxygenionsathightemperatures.Therefore,whena
Zirconia-plated element with platinum electrodes on both sides is heated up in contact with gases having different
partial-oxygen pressures on each side, the element shows the action of the concentration cell. In other words, the
electrode in contact with a gas with a higher partial-oxygen pressure acts as a negative electrode. As the gas comes
in contact with the Zirconia element in this negative electrode, oxygen molecules in the gas acquire electrons and
become ions. Moving in the Zirconia element, they eventually arrive at the positive electrode on the opposite side.
There,theelectronsarereleasedandtheionsreturntotheoxygenmolecules.
Thisreactionisindicatedasfollows:
Negative electrode: O2 + 4e 2 O 2-
Positive electrode: 2 O 2- O2 + 4 e
TheelectromotiveforceE(mV)betweenthetwoelectrodes,generatedbythereaction,isgovernedbyNernst’sequa-
tionasfollows:
E = -RT/nF ln PX/PA........................................Equation (1)
Where, R:Gasconstant
T: Absolutetemperature
n: 4
F: Faraday’sconstant
Px: OxygenconcentrationinagasincontactwiththepositiveZirconiaelectrode(%)
Pa: OxygenconcentrationinagasincontactwiththenegativeZirconiaelectrode(%)
 AssumingtheZirconiaelementisheatedupto750˚C,thenweobtainequation(1)above.
E = -50.74 log (Px/Pa) ................................. Equation (2)