On-line Analysis versus Laboratory Analysis

For a laboratory analysis the sample will be pre-conditioned and the analyser will operate under ideal circumstances as stable temperature, constant pressure, clear filtered product, no flow etc.

Under these conditions the analysis can be defined as an absolute analysis methode; the analysis result is correct if the analyser will be regulary calibrated with predefined standards.

For on-line measuring equipment the situation is different. On-line analysers have to deal with a lot of varying process conditions as temperature, pressure, composition, color, flow, contamination...etc.. and properties as product coating on surfaces, presence of fixed particles and so on. These influences makes that an on-line analyser can never be used as an absolute measuring method. For that reason the measuring result of the analyser must be compared with a laboratory method. The laboratory method is also the reference for the on-line analyser.

During the calibration procedure of the on-line analyser the instrument 'learns' how to measure the concentration of the product, including the disturbing influences as mentioned above.

Because of the calibration procedure of an on-line analyser you can conclude that it is not the measuring principle of the applied analyser that determines the suitability of the analyser in a specific application, but much more the ability of the analyser to handle the problems caused by the earlier mentioned disturbing influences in its application.