Limitations of On-Line Analysers

In spite of the inherent advantages of on-line sensors/monitors, their wide application is still limited
due to the following reasons :

1. On-line monitoring suffers from more problems than laboratory-based methods because to date, the majority of on-line monitoring technologies developed are direct adaptations of traditional, laboratory-based analytical methods which were not originally designed for field applications.

Instead they are required to operate in extreme and variable measurement environments. Consequently, these methods require frequent calibration and maintenance.

2. In addition the analysers are often influenced from cross responses due to matrix variations between the standards and samples analysed, as the measurement conditions are not controlled.

3. Changes in sample matrix affect on-line analysers making it difficult to obtain continuous, reliable measurement in the field.

4. There are also significant economic and logistic costs associated with maintaining remote equipment, as it is difficult for operators to detect problems such as sensor fouling.

5. The problems associated with conventional on-line analysers are due to the fact that univariate linear calibraton models derived from Gauss’s theory of least squares are employed to determine unknown concentrations. Therefore, the samples and standards must be measured with equal care, under the same measurement conditions, to obtain reproducible and accurate results. Since such consistent measurement conditions are rarely present in the field this affects the operating conditions required for reliable performance and causes a high degree of unreliability in the results from online instrumentation.

6. Due to this reason the users/regulatory authorities need to frequently validate their online results with laboratory based methods.

7. The cost associated with maintenance of these conventional instruments has also greatly limited
their wide spread application.

NOTE : The industry must take full preview of available technologies while product selection and above referred limitations have to be curtailed.