Analytical chemistry offers several versatile measurement techniques and an even larger number of application areas. Over the years there has been an impressive growth in application areas and this growth is showing an ever increasing trend. However, the applications of analytical techniques are not limited to laboratory measurements only. The techniques have seen a parallel growth in process monitoring applications in industrial sectors in pace with ever increasing consumer demands.
The basic concepts and operational principles are the same for laboratory as well as process control and monitoring instruments. The need for monitoring of industrial process streams arose because of its ability to provide real time results for taking instant decisions to control processes and prevent economic losses and maintain consistent product quality.
Laboratory instruments are the fore-fathers of industrial process control and monitoring instruments. Common process control and monitoring parameters include pH, temperature, humidity, conductivity, viscosity, absorbance and composition. Laboratory instruments in addition can provide a wealth of information on material properties.
Laboratory instruments are versatile and can be used for making observations on samples in different matrices such as solids, liquids and gases. It is possible to pre- treat samples by filtration or extraction to isolate the analyte(s) to be determined and such pre-treatment procedures can provide results of highest resolution and reliability. Laboratory instruments have high degree of sophistication and can be fitted with a range of accessories to widen the scope of applications. The instruments show a high degree of sensitivity to changes in analyte concentration as they are not subjected to harsh operating conditions as faced by process instruments.
Due to their high sophistication it becomes necessary to provide specialized training to operators for placing reliance on the results.
Process Monitoring Instruments
In contrast to laboratory instruments process instruments are designed to be monitor a single parameter in a process stream and display the reading in real-time or at periodic intervals in convenient analog or digital units. A log of such observations can be maintained automatically for subsequent detailed analysis.
A basic requirement for such instruments is that their sensors should be able to withstand harsh conditions such as high temperatures or pressures, humidity variations, viscosity of materials and high levels of suspended particulate impurities. Such instruments are expected to perform unattended for 24 hours a day for days, weeks or even months without the need for preventive maintenance. The calibration should be valid for such long periods and auto calibration at pre- defined intervals should be possible.
Some process instruments have inbuilt features or sample pre-treatment and filtration but it is advisable to monitor such facilities as failure to do so can lead to problems.
Process monitoring instruments are generally limited to on–line process measurement of a single parameter and add on accessories are generally not needed. In case of absorbance measurements the observations are limited to single wavelength monitoring and fibre optic probes can help interface of the probe to a remote spectrometer. The sensors of process instruments should be rugged enough to withstand the harsh operating conditions.
Process monitoring instruments due to their ability to operate unattended and with little or no maintenance do not require specialized training and even partially skilled work force can handle such instruments.