(1) When selecting a process gas analysis instrument, it is necessary to fully understand the characteristics of the process medium of the analyzed object, the technical performance of the selected instrument and other restrictive conditions.
(2) The technical performance and economic effects of the instrument should be fully evaluated, so that it can play its due role in ensuring product quality and production safety, increasing economic benefits, and reducing environmental pollution.
(3) The technical requirements of the selected analytical instrument detector should be able to meet the operating temperature, pressure and material properties of the analyzed medium, especially the requirements of all background components and contents.
(4) The technical indicators such as selectivity, scope of application, accuracy, range, minimum detection volume, and stability of the instrument must meet the requirements of the process flow, and should be reliable in performance and easy to operate and maintain.
(5) Analytical instruments used in corrosive media or installed in flammable, explosive, or hazardous locations shall meet relevant conditions or meet the requirements for use after necessary measures are taken.
(6) The linear range and response time of analytical instruments used in the control system must meet the requirements of the control system.
- Sampling requirements
(1) The samples taken from the sampling point should be representative, and should not cause changes in composition and content after passing through the sampling system.
The sampling port should be set in a place easily accessible to maintenance personnel, and the temperature, pressure and lag time of the sample should be taken into consideration.
The sampling port cannot be selected in the low-velocity area where the fluid is laminar and the vortex area and dead angle downstream of the throttle.
(2) The gas sample should avoid liquid mixing, and the liquid sample should avoid entraining gas. If the process pipeline wall is easy to adhere to dirt, the sampling probe should be inserted into the center of the pipeline. When the sample contains solid particles, a filter must be installed at the sampling place and a back-flush interface must be provided.
(3) According to the sampling process, the sampling system should have corresponding functions such as pressure reduction and steady flow, condensate discharge, overpressure venting, negative pressure suction, fault alarm or high temperature resistance.
(4) If condensation occurs during the sampling process, heat preservation and heat tracing measures must be taken, but overheating should avoid changes in the sample composition.
(5) The sampling pipeline should be as short as possible to minimize the lag time. The lag time of the sample delivery system should generally not exceed 60s. The diameter of the sampling tube is generally φ6×1mm, but the maximum diameter of the sampling tube should not be greater than φ14×2mm.
(6) The sampling tube is generally made of stainless steel. If the sample contains components that corrode the stainless steel tube, other suitable materials such as polyvinyl chloride and polytetrafluoroethylene can be used. Seamless steel pipes can also be used for non-corrosive dry samples. In addition, anti-blocking measures should be taken for the sample guide pipeline.
- Pretreatment device
(1) Pretreatment devices generally include condensers, coolers, vaporizers, filters or purifiers, as well as treatment devices using chemical or physical methods to ensure the selectivity of analytical instruments. Its composition should be determined according to the specific sample conditions and the technical requirements of the analytical instrument. Generally, it should be configured by an analytical instrument factory.
(2) After passing through the pretreatment device, the sample should be clean, representative, free of harmful components, and meet the technical requirements of the analytical instrument detector for the sample.
(3) After passing through the pretreatment device, the concentration or composition of the component to be tested should not be affected.
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