Eaton KK650 Instruction Manual

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Eaton KK650 Instruction Manual Manual pdf 17 page image

INM MTL 130-0202 Rev 4135 CALIBRATION5.1 General notesProvided the katharometer does not become contaminated, instruments can be expectedto hold their calibration repeatability to better than 0.02% hydrogen for a lengthy period.Chlorine accuracy varies according to air and hydrogen concentrations. In the 90 to 100%range it is approximately 0.5% going out to about 1.5% at lower concentrations with highhydrogen. If the ratio of oxygen to nitrogen varies then a small error is introduced into thechlorine measurement. For every 1% oxygen variation the apparent chlorine concentration ischanged by 0.07% (higher oxygen gives higher chlorine).5.2 Gases requiredTo avoid the need to handle hazardous gases, calibration may be performed using benignsurrogate gases. The surrogate gases used are; 1.5 - 2% hydrogen in air (50% LEL mixture)as a substitute for hydrogen in chlorine, and 100% argon in place of chlorine.Another, even more convenient, way to calibrate the chlorine span of the analyser is touse the process sample gas - assuming its composition is reliably known from other formsof analysis. Configuration Screen 4 (see configuration diagram in section 3), allows boththe chlorine and hydrogen concentrations (see following Note) to be set for the gas usedfor calibration. For example, if the process sample analysis was 96% chlorine and 0.3%hydrogen, this is what would need to be entered in Configuration Screen 4.NOTEThe hydrogen concentration set in Configuration Screen 4 is to enable the analyser tocompensate for its presence when calibrating the chlorine span on process sample – it isNOT a part of calibrating the hydrogen span. The latter is performed using hydrogen inair and specifying the hydrogen concentration in Configuration Screen 3. The hydrogenconcentration set in Screen 4 must be zero if pure gases (i.e. 100% chlorine or 100%argon) are used to calibrate the chlorine span.The calibration process must be performed in the order of1. Zero calibration (air)2. Hydrogen span (2% hydrogen in air)3. Chlorine span (100% chlorine, or 100% argon or process gas if analysis is known)Air is the ‘zero’ gas, and is common to both surrogate and non-surrogate calibrationprocesses. It is possible to calibrate using both surrogate and non-surrogate gases. So it ispossible to zero on air, set the hydrogen span using hydrogen in air, and then set the chlorinespan using either pure chlorine or argon, or the process gas if its analysis is reliably knownand the hydrogen and chlorine concentrations are entered as described above. For bestaccuracy, pure chlorine should be used for setting the chlorine span.NOTEHydrogen in chlorine mixtures can only be generated on-the-spot because they are unstable.Outside of the laboratory the practical difficulties of making these mixtures rule them out ofbeing used.continued on next page