In the span of 60 to 70 years, Analysis has been one of the important aspect in any industrial application whether it is related to chemical, pharmaceutical, fertilizers, refineries, oil exploration fields, coal extraction units, and many more. Any process outcomes with certain amount of fixed desired products along with unexpected or undesired products. Any solution/fluid/service comprising of multiple components in it has to be identified, measured and displayed. This phenomena of identifying, measuring and displaying the results of a solution/service/fluid by taking a sample of it from the process, is called Analytical instrumentation. When we talk about analytical instrumentation, it is very important to emphasize on the analytical aspects to which we instrumentation engineers come across; especially some very famous and evergreen running applications of analysis. They are primarily classified as Analysers, Chromatographs, Detectors and Spectrometers.
Analysers are based on multiple principles of working. The most widely used principles till today’s date are Infrared (IR) based, Ultraviolet (UV) based and Electrochemical based. These analysers are used for sensing & measuring gases like, Oxides of nitrogen like Nitric oxide (NO), Nitrogen dioxide (NO2), Nitrous oxide (N2O), Nitrogen (N2), Carbon monoxide (CO), Sulphur dioxide (SO2), Oxygen (O2), Ammonia (NH3), Hydrogen sulphide (H2S), Natural gas. Other industrial parameters like pH analyser, Turbidity analyser, ORP (Oxidation-reduction potential) analyser also come under the roof of analytical instrumentation. All the above mentioned fluids are measured by different-different principles based analysers mentioned previously.
Gas chromatograph:
A chromatograph is an instrument assembly/setup that takes the sample process gas, separates all the components present in it, identifies those separated components individually, measures their quantity/concentration/amount present in the sample gas and displays the results of all those separated components individually on a chart recorder, digital displays, etc. The typical result of a chromatograph is called chromatogram. Chromatographs are of two types. They are gas chromatographs and liquid chromatographs. Both these chromatographs are used in laboratories as well in process fields. In till date cycle of 50 years, chromatographs have been evolved from a big bulky fridge type assembly to compact state of art field mounting types. The difference between gas chromatographs and liquid chromatograph is that in gas chromatograph for separation of sample gas components, carrier used is a gas, mostly helium, hydrogen or nitrogen. In gas chromatograph, the carrier gas carries the sample gas that has to be analysed, through the column containing non-volatile liquid with high boiling temperature and based on the sample gas components solubility in this liquid column, the components start getting delayed with a different rates in terms of coming down through the column because of each component’s own solubility characteristics. This way, the separation of components of the sample gas takes place. When the column is packed with solid media like silica gel, alumina etc., separation occurs based on adsorption of components. In liquid chromatographs, the carrier is solvent with high pressure carrying the sample liquid and interacting with solid adsorbed material in the column, and based on the way & angle of sample liquid components interaction with solid adsorbed material which is generally silica or polymer granules, their passing velocity through this medium changes and hence they get down through the column on different intervals of time and hence they are measured & displayed accordingly. This way the chromatography i.e. the separation occurs in liquid chromatograph. Photo-multiplier tube, Flame ionisation detectors, thermal conductivity detector, are the popular detectors used in today’s common industrial as well as laboratorial applications. They are used in combination with analysis system. The analysis system, which can be a GC or any of the analyser types mentioned above, gives its output as an input to these detectors.
Spectrometers:
Spectrometers are another important pillar of analytical field of instrumentation. Spectrometer also sometimes used as combined package along with a GC. Spectrometers have been gone through nice amount of evolution in last 50 years and have been developed so tremendously that they are world widely used in both commercial as well as industrial applications. Spectrometer is an instrument (assembly/setup) that works on the principle of light absorption, reflection, scattering and fluorescence, by the sample media (gas/liquid/solid). The graphical output comes from spectrometer is called spectrum. Spectrum is also termed to be as range in which variation of physical characteristics of the sample under test is observed and studied. The most widely used spectrometer types are the optical spectrometer which is based on principle of light absorption/emission/reflection, mass spectrometer which is based on principle of mass to charge ratio of atoms/molecules and nuclear magnetic resonance (NMR) spectrometer which works on principle of external magnetic field influence on atoms. Spectrometers are also separation, identification and then measurement based analysis systems similar to chromatograph. Two prime advantages of spectrometers over GCs are the less response time and higher output resolution. Another famous milestone in this field is called Raman spectrometer. Raman spectrometer is based on the light scattering technique and was named after our great physicist Mr C V Raman. All the spectrometers are selected as per their certain areas of application like based on the nature (state) of sample under test, response time required, accuracy & repeatability needed, installation location, digital communication requirements, manual and auto-calibration & sampling requirements and last but not the least, cost availability to run the setup.
Sampling:
All the instruments mentioned above whether it will be a analyser, chromatograph or the spectrometer, all require a sample from the main process gas/liquid/solid which is to be examined for further analysis i.e. separation, identification, measurement and display. Sampling is found to be very simple and mechanical procedure in laboratory and commercial applications, but in process fields, where process upsetting parameters like low pressure, very high temperature, toxic or corrosive fluids and hazardous areas are involved, sampling becomes little tricky and costly. Hence, for the same, considerable sampling systems/assembly are set up for extracting the sample successfully. In recent developments, automatic sampling systems are also running successfully across the globe. Frequency has to be feeded once and then based on feeded frequency/time interval and other authorisational checks, the sampling system automatically and periodically take the sample and hands over to analyser machine to performs the analysis. A typical sampling system consists of sample inlet valves, pressure reduction valves in case the sample is with high pressure like CNG (Compressed natural gas) applications, a suction pump in case the sample is with low pressure or under vacuum, set of filters, analysis chamber/unit, oven for raising the temperature as required, sample waste return/drain/vent valves. The micro-controller responsible for performing the programmed equations ad generating results, LED/LCD display for displaying the results are also part of sampling system panel together representing as a complete analyser system assembled inside a wall mounted panel assembly. There will be cable entries for power and signal cables incoming/outgoing and entries for sample tubing coming from process pipelines, stacks, etc. Sample injection system is another famous term coined for above mentioned aspect, as the sample has to be extracted/taken from the process and then properly injected into the analysis system while maintaining all the intermediate isolations between process and the analysis-sampling assembly, especially in continuous running analyser systems.
Installation:
Installation has been the revolutionary challenge for analytical field of instrumentation, as all the analysers, spectrometers were meant to be used only in laboratories or any relevant environment. But, as the demand of process and operation in field raised the necessities, technological developments were made to bring these analysers, detectors, spectrometers in field. Originally, all these instruments were supposed to be kept in big shelters with air ventilation systems and lot of maintenance and attention costs were engaged. Again, due to competitive markets, compact design trends, the OEMs worked really hard to bring this bulky mini truck size instruments to a shape of normal control valves and even up to a size of typical pressure transmitter. These designs were termed as field mounted designs i.e., insitu designs. That means they can be directly inserted into the process pipeline or stacks and there is no need for a sampling system. Also, these direct mounted transmitter cum analysers are having displays for readings along with their Analog signals outputs that will be 4-20 mA or 1-5 VDC signal as well as they provide support for serial communication like RS232/485. However, considering vast field of applications, all the installation practices mentioned above are followed. They may be basically direct online mounting or offline mounting through a sampling system in nearby vicinity of 3 to 5 metres or even far located in some shelter or in air conditioned rooms as per permissible parametric conditions. Industrial gas chromatographs, spectrometers, detectors used in process fields are generally kept considering the hazardous areas associated in field. Air conditioned shelter or at least a typical sun shade canopy is provided as roof to these instruments located in field.
Hope the above article might be helpful to you for getting brief information & overview about analytical instruments and their role in overall Instrumentation engineering field. For additional more specific technical information on this topic and sub-topics related & relevant to it, please feel free to write us at [email protected] .Your all doubts & queries will be answered. Also, necessary articles or even training sessions can be arranged & provided for the same, if required by you.
Have a Happy Learning…!
