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Instrumentation Engineer: Next steps for Professional Development

There are a variety of certification courses that an instrumentation engineer can take to improve their career. Here are a few options:

• 
  Certified Control Systems Technician (CCST) - offered by the ISA (International Society of Automation) - This certification demonstrates an individual's knowledge and understanding of the principles of control systems and the ability to apply that knowledge in the workplace.
  
• Professional Engineer (PE) - offered by the National Council of Examiners for Engineering and Surveying (NCEES) - This certification demonstrates an individual's knowledge and understanding of the principles of engineering, and the ability to apply that knowledge in the workplace.
• Certified Measurement & Control Technician (CMCT) - offered by ISA - This certification demonstrates an individual's knowledge and understanding of measurement and control systems, as well as the ability to apply that knowledge in the workplace.
• Six Sigma Green Belt or Black Belt - offered by multiple organizations - Six Sigma is a data-driven approach to improving process efficiency and quality. Green Belt and Black Belt certifications demonstrate an individual's understanding of the Six Sigma methodology and the ability to apply it in the workplace.
• Advanced Process Control Engineer (APC) - offered by the ISA - This certification demonstrates an individual's knowledge and understanding of advanced process control techniques, as well as the ability to apply that knowledge in the workplace.

It's important to note that most of this certifications require both a certain level of experience and completing a specific exam, as well as having a valid engineering degree/diploma .Additionally, you should research the certification requirements and ensure that it aligns with your career goals and the specific industry you're in or want to be in.

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Career improvement ideas for Instrumentation Engineers working in Construction Companies

 Are these your questions in mind??

"Navigating Your Career as an Instrumentation Engineer: Opportunities and Strategies for Success"

or

"From Construction to Control: Charting a Successful Path for Instrumentation Engineers"

or

"Career Advancement for Instrumentation Engineers: Tips, Strategies and Opportunities"

or

"Instrumentation Engineer: 10 years' experience, what's next?"

Then this post is for you.

If you're an instrumentation engineer with 10 years of experience working in a construction company, there are a few different career paths you could consider, depending on your interests and goals. Here are a few suggestions:

Transition into a role in an engineering company: You could leverage your experience working in construction to transition into a role in an engineering company, where you would be responsible for designing and implementing instrumentation systems for process control and automation.

Specialize in a specific area of instrumentation: Consider focusing your efforts on mastering a particular area of instrumentation, such as process control, advanced control systems, or industrial automation. This could help you differentiate yourself in the job market and open up new opportunities.

Project management: With your experience, you could step into a role that manage projects that are related to your domain. As you already have the experience of working in different projects and having a understanding of the construction and production process it can help you to manage projects more efficiently.

Look for roles in the construction industry: While you may be interested in transitioning out of the construction industry, there may still be opportunities for you to use your skills and experience in this field. For example, you could look for roles as an instrumentation engineer or manager in a construction company or in a position that requires experience in process control and automation.

Training and Certification: You could also consider seeking out training and certification in areas that are in demand in your field, such as industrial automation, safety systems, and energy management. This will demonstrate your commitment to professional development and will help you to stay current with the latest trends and technologies in your field.

It's important to remember that every career path will have its own set of challenges and opportunities, so it's important to do your research and carefully consider which path is the best fit for you. It may also be helpful to talk to people who are currently working in the roles you're interested in to get a better understanding of what to expect.

So for Navigating Your Career as an Instrumentation Engineer: Opportunities and Strategies for Success here are the tips:

• Understanding the different career paths available to instrumentation engineers, including roles in engineering companies, construction companies, and specialized areas such as process control and automation.
• Tips for transitioning from a construction company to an engineering company or other specialized role in the field of instrumentation.
• Strategies for developing specialized knowledge and skills in areas such as process control, industrial automation, and energy management to stand out in the job market.
• The importance of continuing education and training, and suggestions for relevant certifications and training programs.
• Case studies or profiles of successful instrumentation engineers who have navigated unique career paths in the field.
• Sharing the challenges and opportunities of being an Instrumentation Engineer
• The importance of networking and connecting with professionals in the field to learn about new opportunities and stay informed about industry trends.

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Turbidity meters

Very often it is necessary to measure the amount of solids suspended in fluids. In this case the turbidity is measured as the function of the amount of suspensions in fluids. Fig. 7.10 schematically explains an operational principle of a transmission-type turbidity meter. A constant-candlepower lamp 1 provides a lightbeam which passes through the lens 2, glass windows 3, and a sample cell 4.

A fluid with solid suspensions to be measured flows through the sample cell. The light beam is scattered by solids in suspensions. The degree of scattering depends on the amount of solids, and hence on the turbidity of the fluid. This scattering effect is called the Tyndall effect. The light beam with reduced intensity falls on the photo cell 5 (usually photosensors), which converts the measured light intensity to an electrical signal inversely proportional to the turbidity of the fluid (or the amount of suspended solids). The scale of a device 6 for measurement of this electrical output signal is calibrated in ppm of solids suspended in fluid. Since the photosensor is temperature sensitive, a heater and thermostat are employed to maintain its temperature at a constant value. By matching the length of the light path to the level of turbidity, we can vary ranges of turbidity to be measured.

The formation of deposits on the windows of the sample cell reduces the accuracy of turbidity measurements, so frequent maintenance of these windows is required.

Article Source:: Dr. Alexander Badalyan, University of South Australia

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Flame ionisation detectors (analysers)

Another type of a gas detector is widely used not only in the gas chromatography, but as a separate gas analyser as well. At present it is the most sensitive gas detector used in gas chromatography. Its operational principle is based on the measurement of ion current which is developed in a flame where the ionisation of organic compounds takes place. This detector is sensitive to organic compounds, whereas it does not give response for inorganic gases.

Figure 7.9 shows a schematic view of a flame ionisation detector. A carrier gas 1 (usually nitrogen) from the outlet of a separating column of a gas chromatograph is mixed with hydrogen 2, and this mixture is burned in the atmosphere of air 3 in the detector jet 4. Since even small amounts of compressor oil could effect the results of measurements, molecular sieves or a diffusion disc 5 are used to eliminate the oil from the supplied air. An ignitor coil 6 is used to ignite the nitrogen-hydrogen-air mixture leaving the jet. When this gas mixture burns very few ions are developed. A collector of ions 7 is placed above the jet close to the flame. In order to maintain ion flow from the jet to the collector the latter is kept at some positive electric potential (75-150 V) above the normally grounded jet. Thus produced the background ion current passes through the conductors via the insulated feed-through 8 to an amplifier. Then the background current is balanced (brought to zero). Now, when an organic compound leaves the separating column of the gas chromatograph, enters and burned in the jet, large amount of ions are formed in the flame. This increases the ion current (up to 10^-12 A), which is amplified in an amplifier. The compound burned in the flame. Thus we can evaluate the amount of the organic component in the analysed gas mixture.value of this current is proportional to the amount of the organic.

Figure 7.9. Schematic of a flame ionisation detector (analyser).

For simple molecules the detector response is proportional to the carbon content in the compound, whereas in the case of other compounds the response is not easy predictable. These detectors are not as temperature sensitive as thermal conductivity detectors. As we mentioned above, these detectors can be used for continuously measurements of the total hydrocarbon content in the gas mixture. In this case they are called hydrocarbon analysers.


Article Source:: Dr. Alexander Badalyan, University of South Australia

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Thermal conductivity gas analysers

One of the simplest and earliest method for measurement of composition of binary gas mixtures is a method which uses thermal conductivity properties of gases. By passing the gas to be analysed over an electrically heated filament, and thus cooling the filament to an extent that is dependent on the thermal conductivity of the gas under measurement, we can determine the gas composition. The only drawback of this method is that it can be employed only to binary gas mixtures, since this analyser measures the total sample thermal conductivity, and cannot, therefore, distinguish what composition change causes the conductivity variation. However, this technique is widely used in gas chromatography for detection of the constituents of a separated gas mixture. Although they respond to most types of gas samples, thermal conductivity detectors are much less sensitive than flame-ionisation detectors.

Table 7.1 gives values of thermal conductivities of several gases (from Huskins D.J. Quality measuring instruments in on-line process analysis, Ellis Horwood Ltd., NY, 1982, p. 199). In this table k is thermal conductivity of a gas.

Table 7.1. Thermal conductivities of some gases.

A thermal conductivity gas analyser consists of three major parts, namely, measuring cell, regulated power supply and Wheatstone bridge, and a case temperature control. Fig. 7.7 shows a schematic of a four-element thermal conductivity cell. This cell presents a relatively large mass of metal (stainless steel with high thermal conductivity coefficient) to provide a stable heat sink. Flow passages and cavities are drilled in this metal for gas flow and for placement of heat-source-sensing elements, namely, hot wire filaments. These filaments may be made of platinum, platinum alloy materials, or tungsten. The filaments are used in pairs, two filaments are placed in the stream of the sample gas, and two others - in the stream of a reference gas. Increasing the number of filaments (up to eight) will increase the sensitivity of the analyser. Temperatures of these filaments are varied from 200 to 400 Deg C.

The second element of the thermal conductivity gas analyser is a regulated power supply and Wheatstone bridge (see Fig. 7.8). The Wheatstone bridge uses a high-quality regulated power supply, which delivers current between 100 and 300 mA dc. The stability of the analyser depends mostly on the accuracy of a power supply voltage regulation. Electrical terminals of filaments from thermal conductivity cell are connected to the sides of the Wheatstone bridge, filaments which are placed in the sample stream being connected to opposite sides of the bridge, the same refers to the filaments placed in the reference gas stream.

In order to increase stability of the measuring thermal conductivity cell one need to be able to maintain a constant temperature environment in it. For this purpose several types of case temperature control systems utilising on/off thermal switches are used.

Figure 7.7. Four-element thermal conductivity cell.

The four-element thermal conductivity cell is connected to the Wheatstone bridge (see Fig. 7.8). A sample of a gas or a binary gas mixture (flow controlled from 50 to 200 cm3) to be analysed is passed through the measuring cell and across the filaments 1 and 2, placed in the cavities of this cell. A reference gas (usually single component gas representing the major component of the gas mixture under investigation) passes across reference filaments 3 and 4. The flow of the reference gas is controlled from 40 to 100 cm3. The reference gas is used to provide better stability due to variations of temperature and barometric pressure. A current from the regulated power supply 5 is measured by an ampermeter 7, and this current heats the filaments. The surface temperature of filaments increases. When analysing gas passes across the filaments 1 and 2 this heat energy is conducted away from the filaments. The higher the thermal conductivity of the gas under measurement (comparing to that of the reference gas) the more heat energy is removed from the measuring filaments 1 and 2 than from the reference filaments 3 and 4. Therefore, temperature of the measuring filaments will be lower than temperature of the reference filaments, and an electrical resistance of the measuring filaments will be lower that that of the reference ones. This will cause an unbalanced condition of the Wheatstone bridge (current flows through the ampermeter 6), the degree of this unbalance being dependent on the composition of the gas under measurement. To bring the bridge to a new balanced condition a slide resistor 8 is used. The scale 9 of this resistor is calibrated in the units of gas composition.

Figure 7.8. Wheatstone bridge with a thermal conductivity cell.


Development of an equation for output voltage of TCD:
(from Bentley J. P. Principles of Measurement Systems, Longman, 1995, p. 338-340):

Vab is a measure of a gas concentration. Convective heat transfer coefficient U between filament and moving gas is a function of gas thermal conductivity, k , and the average gas velocity. If gas velocity is maintained constant, then.

 The value of a constant self-heating current is determined as follows:

(7.9)

where,   I - total bridge current, A.

The steady-state heat balance equation:

where

Since terms involving
are negligible, then

Substitute (7.14) into (7.10):

where,

 (7.17)

if  then :

(7.18)

Resistances of filaments in measuring cells are equal to:

(7.19)

Resistances of filaments in reference cells are equal to:

(7.20)

(7.21)

For a typical system:

, and , equation (7.21) can be rewritten as follows:

(7.22)

Below is thermal conductivity of a gas mixture:

(7.23)

(7.24)

where, the function of velocity of gas stream can be determined as follows:

(7.25)

Here we used the following parameters:

The resistance measurements tends to drift with time because of vaporisation of a platinum filament and because of reactions between the filament and the gas under measurement. To reduce this drift glass coatings of the filament are used, but this will reduce the response of the analyser. Sample gas temperature may vary from 1.7 to 43 Deg C, ambient temperature - from -1 to 38 Deg C. For binary gas mixtures an accuracy of thermal conductivity gas analysers is equal +/-2% of full scale.

Article Source:: Dr. Alexander Badalyan, University of South Australia

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pH meters (hydrogen ion concentration)

Acids and bases are significant in food and chemical industries, water and sewage treatment, biology, medicine, etc. Therefore, we need to be able to measure concentration and strength of acid and base solutions. Instrumentation has been developed to measure pH of solutions using special selective electrodes that can develop an electromotive force, which is proportional to the hydrogen ion concentration in the solution where these electrodes are immersed.

What we understand under the term of pH? How is it related to the concentration and strength of solutions?

It is known, that acids and bases produce conductive solutions, when dissolve in water, because charged ions are formed. Here are ionisation equations for hydrochloric acid and sodium hydroxide dissolved in water:

If we mix these two aqueous solutions, the acidic and basic properties of the solution will be lost, so the neutralisation reaction occurrs:

Water is formed as the result of this reaction. However, the resulting solution is still conductive, because of the presence of sodium and chloride ions. If the quantities of initial acid and base are equal, then this resultant solution will be neither alkaline, nor acid.

In the case of dissociation of pure water, ions of hydrogen and hydroxyl are formed:

Pure water is very weak regarding to dissociation. So, very small amount of water molecules break into ions. The symbol Û  in (7.4) indicates that the process consists of two reactions, namely, dissociation of molecules into ions and recombination of ions into molecules. 

Fig 7.6A : Dissociation and formation of hydronium.

For pure water the rates of these two reactions are equal, and we can write an equilibrium equation as follows:

where,

Since pure water is neutral, then according to (7.5) the activity of hydrogen and hydroxyl ions should be equal, ie, 10-7  mole/l. No matter what compounds form an aqueous solution, the product of activities of hydrogen and hydroxyl ions should always be equal to 10-14  mole/l at 25 °C.

With an addition of a strong acid (such as HCl) to pure water we add many hydrogen ions. As the result of this addition, the number of hydrogen ions will increase, let’s say to 10-2  mole/l, and the activity of hydroxyl ions then will be equal 10-12  mole/l. As we can see, the product of activities is still equal to 10-14  mole/l at 25 °C.

Since the use of ion activities in the form of a power representation is not convenient, a Danish biochemist S.P.L. Sørensen in 1909 proposed to use the expression of pH, which was originally derived from the phrase “power of hydrogen”. The pH is defined as a negative common logarithm (with the base of ten) of the hydrogen ion activity, as follows:

Therefore, the pH of pure water is equal to 7 at 25 °C. Acid solutions contain more hydrogen ions than hydroxyl ions, so the activity of hydrogen ions will be greater than 10-7 , that is, 10-6, 10-5, 10-4, 10-3, etc., with pH equal to 6, 5, 4, 3, etc., respectively. pH values for basic solutions will be 8, 9, 10, 11, etc., respectively.

Instrumentation for pH measurements use an electrometric method. A glass pH-responsive electrode immersed in a solution under measurement will vary electric potential (voltage) on the boundary between the electrode and solution as a function of pH of this solution. However, it is not possible to measure the potential between this electrode and solution only. Why? Because when we connect a measuring device, another potential is developed between the solution and a conductor which connects the measuring device and the solution, this new potential being also dependent on the pH of the solution. Therefore, we need to use one more electrode, the reference electrode, which potential is not dependent on the pH of the solution. In order to make the potential of the reference electrode not dependent on the pH of the solution, it should be filled with a saturated solution.

Figure 7.6. Schematic of a pH-meter with the glass and reference (calomel) electrodes.

Fig. 7.6 shows schematic of a pH-meter. A glass electrode 1 and a reference electrode 2 are immersed in a solution 3 under measurement. The potential difference between these two electrodes which is proportional to the pH of the solution is measured by a potentiometer 6. The glass electrode is filled with the solution 4 with a known value of pH. A silver-silver chloride electrode 5 is placed inside the glass electrode. The reference electrode presents a dielectric enclosure 2 filled with pure mercury 7. A low soluble mercury-mercury chloride 8 (calomel) is placed above mercury. The reference electrode is filled with a saturated solution 9 of KCl. A semipermeable membrane 10 is used to produce an electrical contact between KCl solution and the solution under measurement 3. Potassium chloride diffuses or leaks into the solution under measurement, so the concentration of KCl in the reference electrode is not changed. An electrical circuit consists of several elements connected in series, and an overall electromotive force is equal to the sum of these potentials, as follows:

where,

E_S - the overall electromotive force developed in the circuit, mV;
E₁ - potential between a silver-silver chloride electrode and the solution 4, mV;
E2 - potential between the solution 4 and an internal surface of the glass electrode, mV;
E3 - potential between mercury and calomel in the reference electrode, mV;
Ex - potential between an outside surface of the glass electrode and the solution under measurement, mV.

E1, E2 and E3 are not dependent on the pH of the solution under measurement, but vary with temperature. Ex depends on the pH of the solution under measurement and its temperature, and can be evaluated by the Nernst equation:

where,
R - the gas law constant, R = 8.31451 J/(mole*K);
T - absolute temperature of the solution under measurement, K;
F - Faraday’s number, F = 96485.309 C/mole, C - coulomb.

The overall electromotive force at a constant temperature is the function of the pH of solution only. However, one need to introduce a temperature compensation element (usually a suitable packaged resistor, thermistor, or resistance temperature detector), which is placed close to the glass electrode in the solution under measurement and connected to the electrical circuit for electromotive force measurement.

Article Source:: Dr. Alexander Badalyan, University of South Australia

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Electrolytic conductivity meters

An operational principle of electrolytic conductivity meters is based on the relationship between electrical conductivity and concentration of solutions.

The ability to conduct electricity is called electrical conductance, which is reciprocal of electrical resistance:

electrical conductance = 1/electrical resistance.

The unit for electrical conductance is Siemens: 1S = 1/Ohm.

Electrical conductivity is equal to electrical conductance of a volume of the material of unit length and area:

electrical conductivity = electrical conductance*length/area.

The unit for electrical conductivity is S/m. Few solutions exhibit electrical conductivities as great as 1 S/cm. So, the most commonly used units are mS/cm and mS/cm.

Electrolytic conductivity is usually defined as electrical conductance of a unit cube of solution as measured between opposite faces. It has the same units as electrical conductivity.

In conductive or electrolytic solutions positive ions (cations) move toward the cathode, and negative ions (anions) move toward the anode. Reduction and oxidation take place on the cathode and anode, respectively. Electrolytic conductivity of a solution mostly depends on the concentration and mobility of all ions in the solution. The latter depends on the ion size, charge, dielectric constant of the solvent, temperature and viscosity of the solution. Electrolytic conductivity of a mixture of solutions is proportional to the sum of relative concentration of each components and the mobility of ions. Therefore, conductivity meters are used for electrolytic conductivity measurements of one component solutions only. Fig. 7.4 shows typical conductivity curves for NaCl solution in water.


Electrolytic conductivity is usually measured by placing electrodes in contact with an electrolytic solution. In this case electrical conductance between electrodes is related to electrolytic conductivity of the solution. Since the conductivity cell has unchanged dimensions, so by measuring electrical conductance of the solution in this cell, and thus determining the cell constant, we can relate thus measured electrical conductance to the actual value of electrolytic conductivity.


Fig. 7.5 schematically shows an electrolytic conductivity meter, which employs an alternating current Wheatstone bridge in order to avoid polarisation of measuring electrodes. A conductivity cell is immersed in the solution 1. This cell consist of an insulating shield 2 made of either glass or epoxy, or polystyrene, or Teflon. Two metal electrodes 3 are placed inside this shield. These electrodes are made of either stainless steel or nickel, or platinum, or gold, or platinum-plated metals. The shield is perforated to provide good contact of solution with these electrodes. The operational principle of a Wheatstone bridge is described in 3.5. We measure an electrical resistivity (r) of the electrolytic solution between cell electrodes. An electrical resistivity is defined as an electrical resistance of a conductor of unit cross-sectional area and unit length, as follows: r=R*A/L, (Ohm*m), where, R is the electrical resistance of the conductor (Ohm), A is the cross-section area of the conductor (m2), and L is the length of the conductor (m).

Figure 7.4. Electrolytic conductivity of NaCl solutions. 

Since temperature of an electrolytic solution has influence on its electrolytic conductivity, therefore, we should be able to introduce temperature correction (compensation). For this purpose an electrode sensor filled with a reference liquid, which has a thermal coefficient of electrolytic conductivity approximately equal to that of the measuring solution, is employed. This sensor is immersed in the measuring electrolytic solution near the measuring conductivity cell, and through conductors is connected to the side of the bridge adjacent to that side of the bridge which is connected to the measuring conductivity cell. Since temperatures of the conductivity measuring cell and the sensor cell are equal, then variations of temperature of the electrolytic solution will not have influence on the results of electrolytic conductivity measurements.

Figure 7.5. Electrolytic conductivity meter.

Article Source:: Dr. Alexander Badalyan, University of South Australia

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On-line chromatographic analysis

As early as 1903-1906 a Russian botanist Mikhail Tsvet (Lecturer in the Warsaw University) performed experiments trying to separate pigments of plants. Using a solvent, petroleum ether, he washed the pigments through a vertical glass tube filled with a powder-like absorbent, calcium carbonate. As the result of this procedure, he obtained a series of coloured absorption bands. He first used a term ‘chromatography’ to describe this method. Word ‘chromatography’ consists of two words ‘chromatos’ (in Greek language means ‘colour’) and ‘grapho’ (in Greek language means ‘writing’), and means ‘colour writing’. By coincidence, the surname ‘Tsvet’ in Russian language means ‘colour’.



Chromatography methods are classified regarding to the types of moving and stationary phases according to Figure 7.1. (from Considine D. M. Process Instruments and Controls Handbook. McGraw-Hill Book Company, Sydney, 1985, p. 6.170).

Figure 7.1. Classification of chromatography methods. 

Physical absorption principles for separating of various components from a mixture of chemical substances form the basis of chromatography (see Fig. 7.2). A gas mixture 1 to be analysed is carried through a tube or column 2 by an inert carrier gas (nitrogen, helium) 3. The gas mixture and the carrier gas form the moving phase. The column is filled (packed) with materials 4, the stationary phase, which will absorb gases. Different components of the gas mixture are delayed for varying increments of time. After the column, the separated gases 5 pass through a gas detector (flame ionisation detector, or thermal conductivity detector) 6. This detector develops a signal 7, which then is transformed to the chromatogram 8. Using this chromatogram we can determine the type of a component and its quantity. In order to achieve better separation of components from various mixtures different types of packing materials should be chosen. The absorption of components by the stationary phase is highly dependent on the operational conditions. Therefore, temperature, flowrate and pressure of a carrier gas, sample valve timing, and detector sensitivity should be carefully controlled.

Chromatographs are widely used for composition measurements of gaseous and liquid mixtures. Usually they are complex laboratory equipment. Modern on-line chromatography systems for continuous, repetitive and fully automatic gas analysis have been developed, and in principle have all essential elements inherent to laboratory-type equipment. Fig. 7.3 schematically shows an operational principle of an on-line gas-chromatograph.

Figure 7.2. Schematic of a gas-chromatograph (gas-solid chromatography). 

A sample of a gas mixture 1 is withdrawn continuously from a process unit 2 and through a shutoff valve 3, filter 3a (for removing of particulate matter) and pressure regulator 4 (for reducing pressure to a lower constant value) circulates through a sample conditioning unit 5. After the sample conditioning unit the stream enters the process 6 through a shutoff valve 7 in the point of a lower pressure compared with the sample withdrawal point. The sample conditioning unit allows to calibrate the gas-chromatograph with the synthetic calibration blend from a container 8, through a pressure regulator 9, and to control flowrate. A carrier gas (nitrogen, helium) is supplied from a cylinder 10, and its pressure is controlled by a pressure regulator 11 and a pneumatic control section 12. An analyser 13 contains separating columns, flame ionisation and/or thermal conductivity detector(s) and a temperature control unit. A metering pump, which is placed in the sample conditioning unit, injects a small sample of an already conditioned gas mixture into the separating column, which is placed in the analyser. An electronic module 14 stores analytical programs in RAM and controls functions of the analyser. Analytical data are transferred from the electronic module to a data processor 15, where they are converted to analog signals. These signals are transmitted to a bar graph recorder16 and a number of trend recorders 17. A host computer 18 controls all actions of the chromatograph, receives results, alarm messages, stores application programs. A real-time chromatogram is printed on the printer 19. 

Here are several values of parameters of a chromatograph:

• temperature in the temperature control unit - 40 to 200 °C;
• accuracy of temperature control - ±0.2 °C;
• total length of separating columns - 10 m;
• diameter of separating columns - 3 mm;
• flowrate of a carrier gas - 40 to 160 cm³/min;
• volumes of samples of gas mixtures - 0.5, 1, 2, 4 cm³;
• volumes of samples of liquid mixtures - 0.004, 0.008, 0.032 cm³;
• pressure of a gas carrier - 400 kPa;
• output signal - 4 to 20 mA.

An output signal from a gas-chromatograph is usually used as an input signal for a controller, which changes either process temperature or pressure or flowrate, etc., to bring a product composition to the desired value.

Figure 7.3. On-line chromatographic system.

Article Source:: Dr. Alexander Badalyan, University of South Australia

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