IEC 61207-3 pdf download – Gas analyzers – Expression of performance – Part 3: Paramagnetic oxygen analyzers
4Procedures for specification
4.1General
The procedures are detailed in IEC 61207-1.This covers:
operation and storage requirements;
specification of ranges of measurement and output signals;- limits of uncertainties;
– recommended reference values and rated ranges of influence quantities (see IEC 60654-1).In this part of lEC 61207, requirements for essential ancillary units and services are given.
Additional characteristics for specification of performance and important aspects of
performance relevant to paramagnetic analyzers are detailed.
4.2Specification of essential ancillary units and services4.2.1Sampling system
The sampling system shall be specified to supply the sample within the rated range ofinfluence quantities of the analyzer.
Simple elements of the sampling system may be included in the analyzer. Sample flowmeters, sample flow regulation, bypass flow meters, bypass flow regulations, sample filtersare often part of the analyzer.
lf certain system elements are included in the analyzer the rated range of influence quantitieswill be less severe compared to an analyzer without any sampling system.
The sampling system will add a delay in addition to the response time of the analyzer.Hence,the sample system response time should be specified.
The chemical composition of the sample stream shall be considered in the system specification.Special precautions need to be taken for flammable samples, toxic samples or corrosive
samples.
Some materials are permeable to oxygen (for example, silicones) and the measurement
uncertainties that may be introduced by them should be considered and avoided if necessary.For systems measuring very high concentrations of oxygen, the sampling system componentsshould be clean for oxygen service to prevent any dangerous reactions with flammable
contaminants.
4.2.2Services4.2.2.1General
Paramagnetic oxygen analyzers will require facilities for calibration after installation. Bottledcalibration gases and pressure regulation facilities are generally required.Quincke analyzerswill additionally require facilities for supplying the reference gas.
NOTE Nitrogen is usually employed for zero calibration. The span gas will usually be a known concentration ofoxygen in nitrogen typically about 80 % of the measuring range. Air contains between 20,64 % and 20,95 % Oz byvolume due to varying humidity. Dry air or instrument air at 20,95 % 0e can therefore be used for span calibrations.lf the oxygen level of the sample gas is high, then 100 % O2 is usually used as the span gas.
4.2.2.2 Rated range of calibration and reference gas pressure
Calibration and reference gas pressure shall be within the rated range of sample pressure for the analyzer, to prevent possible damage to the paramagnetic sensor.
4.2.2.3
Rated range of calibration and reference gas flow
Calibration and reference gas flow shall be within the rated range of sample flow for theanalyzer. For minimum uncertainties, the calibration gas flow should be set the same as thesample flow. Excessively high calibration and reference gas flows can damage the
paramagnetic sensor, particularly from a large pressure impulse,which may occur if the flowoutlet becomes blocked and then quickly released.
4.3Additional characteristics related to specification of performance
4.3.1 The following additional characteristics to those detailed in IEC 61207-1 may berequired to be specified to define the performance of a paramagnetic analyzer or its suitabilityfor a particular application.Depending on the analyzer design details or application, some ofthese additional terms may be omitted.
4.3.2 Hazardous classification of the area in which the analyzer is to be located. Generalpurpose analyzers will not be suitable for location in hazardous areas.
4.3.3 Flammable gases or vapours should only be sampled by analyzers which arespecified as suitable and should be vented from the analyzer in a safe manner.
4.3.4 lf the sample gas is toxic, this should be specified, as special maintenance ins-tructions may be required to ensure leak-free operation. Installation of the analyzer shall alsotake into account how the sample gas is vented, retumed to process, or otherwise dealt with.
4.3.5 The orientation of the analyzer should be considered. In fixed installations,analyzersshould be positioned in an upright manner so that any uncertainties due to tilt are minimized.For installations that move (for example, ships), the rated range of tilt should be specified.
4.3.6 The vibration sensitivity of the analyzer should be considered.For applications wherethe vibration levels are outside the rated range of the analyzer, anti-vibration mountings arerecommended.
4.3.7 The response time of the analyzer and its sampling system should be considered.The response time specified for the analyzer will usually be considerably less than thesampling system, but is dependent on the sampling system design.
NOTESome paramagnetic analyzers are designed with adjustable sample flow and bypass flow sample systems.4.4lmportant aspects related to specification of performance
4.4.1General
Although covered in lEC 61207-1, the following aspects are particularly relevant toparamagnetic analyzers.
4.4.2Rated range of ambient temperature
The performance of an analyzer is normally ambient temperature-dependent and will have adefined operating range of temperatures within which it will operate within its specification.
IEC 61207-3 pdf download – Gas analyzers – Expression of performance – Part 3: Paramagnetic oxygen analyzers
