Inline Or In Situ Analysis

In inline or in situ systems, the sample is not transported from the sampling point to the analyzer because the analyzer is at the sampling point. Probe-type analyzers have been used for a long time. One of the newer probes is the fiber-optic probe (FOP), which uses fiber-optic waveguides to return process-modified light from the probe to the spectrum analyzer usually located in a control room (see Figure 3.12.1). No transfer time or sample waste occurs because the measurement is made on the moving process material.

Another advantage of inline analyzers is that they can be multiplexed; that is, installed at many points in the process. The analyzer's controller oversees the frequency of analysis at each point and directs switching between them.

However, inline systems usually use a window through which light is transmitted and reflected, and this window can cause measurement errors. Process liquids can make the window dirty and cause measurement errors. In addition, the extreme temperatures and safety considerations at the sampling point may not allow for installation of the sensitive electronics that inline systems generally require.

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