ANALYZERS INSTRUMENTATION QUESTIONS AND ANSWERS

ANALYZERS INSTRUMENTATION QUESTIONS AND ANSWERS

E Stands for question suitable for Engineer.

S Stands for question suitable for Supervisor.

T Stands for question suitable for Technicians.

1. What is the definition of the Analyzers? Why it is being used in industry? (S/T)
Answer:
It is an instrument used to analysis the gas, liquid or solid to detect the  component of interest for improve productivity, checking the quality of the product and the component released to air or water, which can effect the human
life as well as environment pollution.
2. What is the on line Analyzer and why it is required? (S/T)
Answer:
Online Analyzer is analysis the gas, liquid or solid at situ to avoid transportation delays, interference with integrity of the sample. Now a days for improve productivity, maintaining the stringent quality of the product and the component released to air or water, which can effect the human life as well as environment pollution, on line analysis has become must.
3. What are major factor effect the reliability and accuracy of any on line Analyzer? (S/T)
Answer:
The factors affect the reliability and accuracy of any on line Analyzer is temperature, flow and pressure. Further, it may please be looked into that sample is free from any dirt or condensation.
4. What is GC? (S/T)
Answer:
It is physical method of separation that is based on differences in solubility (or adsorption) of the substance between a mobile and a stationary phase. It is elution method, the sample is vaporized as a narrow plug, injected into a carrier gas (a mobile phase) and forced to flow through a small diameter tube containing the stationary liquid phase.
5. How many types of Detector of GC you are aware? (S/E)
Answer: They are Thermal Conductivity Detector (TCD) and Flame Ionization Detector (FID), these are popular for their
simplicity and ruggedness. However some other types are Flame Ionization Detector, Orifice Capillary Detector, Photo Ionization Detector, Electron Capture Detector.
6. What is oven temperature generally maintained for a GC? (T)
Answer:
It depends on the specification and selection of the column, which is generally
70˚C to 100˚C.
7. What are the principles of operation of FPD and TCD type GC? (E/S)
Answer:
FPD: It is Flame Photometric. It detects the element specific to flame emission spectrometer.
TCD: The sensing filament and reference filament is heated electrically in the presence of carrier gas i.e. Hydrogen or Helium due to variation in the concentration of sample thermal conduction of the filament changes. This null
voltage change is detected by the bridge.
8. What are the different parts of a GC? (S/T)
Answer:
These are Analyzer, oven, detector, computer, sample handling unit etc.
9. What is the carrier gas and fuel gas are being used for GC? (T)
Answer:
Carrier gas is Helium or Hydrogen with Nitrogen gases. Fuel gas is Hydrogen.
10. What do you know about column and why the same is being used? (E/S)
Answer:  It is capillary SS or Teflon tube of very smaller diameter (1/8”) packed with  chemical compound used for separation, getting stationary phase and faster yield of process sample.
11. Why regeneration of the column is required? (T)
Answer: Some time column gets dirt and the action of packed compound gets exhausted. It
is purged with Nitrogen at constant temperature.
12. What are FT, CT, RT, and TT? (E/S)
Answer: FT is Function Table CT is Component Table RT is Retention time TT is trend Table
13. What are the different  types of outputs available in standard GC to interface with DCS or any third party system? (E)
Answer: These are 4-20 mA DC, 0-5 VDC, RS 232, RS 485, RS 422.
14. How many types of pressure regulators you are aware? (T)
Answer:
Pressure regulator is a critical component of any analyzer. Mainly high and low pressure regulators are there. It can be of Single stage or double stage. Further it has got different type based on the connection to cylinders DIN 1,
DIN 6, DIN 5, DIN 8.
15. Why some cases the sample lines is steam traced? (S/T)
Answer: Some cases the sample lines is steam traced to remove condensation and to keep the process component in it’s original state.
16. What are span gas and zero gas shall be used to calibrate an analyzer of 0- 1000 PPM H2S? (T)
Answer: Span gas will be 800 PPM± 1% and balance nitrogen. Zero gas will be pure nitrogen or air.
17. What is pH? What are domain for neutral, acidic and alkaline nature of a liquid? (S/T)
Answer: pH is negative logarithm of the hydrogen irons (Proton) activity. Neutral is 7.0 above 7 it is Alkaline and bellow 7.0 it is acidic.
18. Wow the pH of a liquid can be measured? (E/S)
Answer: It can be measured by Litmus Paper or electronically through glass electrode.
19. What the standard solutions are available used for the pH analyzer calibration? (E/S)
Answer: 4, 7, 9 are the standard buffer solution generally available to check pH analyzer.
20. Why auto temperature compensation is must for an online pH analyzer? What type of temperature elements is being used for the same? (E)
Answer: pH varies as per Nernst Equation with the change in temperature. Pt 100 RTD (Resistance Temperature Detector) is used as basic temperature element.

21. What is ORP? (E)
Answer: It is Oxidation-Reduction Potential. It is use to infer the concentration of oxidizing or reducing species.
22. What equipment to be used in a sampling system of an extractive type system where the process pressures at draft region? (S)
Answer: Vacuum Pump or ejector.
23. What are the engineering units for flow (as indicated in Rota-meter), pressure (as indicated in Pressure Gauge),  emperature (as indicated in Temperature gauge)? (S/T)
Answer: Flow Gallons per Minuets or SCFH Standard cubic foot per hour, Pressure Kg / Cm2, Psig Temperature Deg ˚C, Deg ˚F
24. Why a PRV is used in a sampling system? (T)
Answer: PRV is Pressure Regulating Valves, it is used to have constant pressure at analyzer end.
25. Define Specific Gravity, Density and what are principle to measure it? (E)
Answer: Density is quantity of matter per unit volume. Specific Gravity is ratio between the density of a process material to that of water or air at specified condition. It can be measure by Vibrating Densitometer, Radiation Densitometer.
26. How many types of Oxygen analyzer have you worked? (E)
Answer: Oxygen analyzers are of Paramagnetic deflection type, calcium stabilized Zirconium Oxide probe type, and Catalytic Combustion type. However Zirconium Oxide probe is the most popular.
27. What is Nernstian equation? (E)
Answer: E (mV) = 0.0496 T (log10 PO / P1) ± C (mV) E = Probe output voltage 0.0496 is Faraday’s gas constant
T is Absolute Temperature (OK) PO is Partial gas reference gas i.e. air P1 is partial pressure sample gas C is Cell constant
28. What are the advantages of in-situ type of Oxygen analyzer over extractive type? (E)
Answer: Insitu analyzer give instant measurement of oxygen at flue gas, which is critical for any auto combustion control loop. Whereas extractive type oxygen analyser has got sample transportation lag, inaccuracy due to moisture and other component. Hence, insitu oxygen analyser is more reliable.
29. What is the normal operating temperature of Zirconia type Oxygen Analyzers? (S/T)
Answer: Normal operating temperature is 700 to 800 OC.
30. What is the reference gas used for Zirconia type Oxygen Analyzers and what is the % contain of the O2 in the same? (T)
Answer: Air and % contain of the O2 contain is 20.9%.
31. How many wires and tubes are connected to typical Zirconia type Oxygen probes head? (S)
Answer: Two wire for cell o/p mV, two wire for cell temperature Thermocouple (K type) and Two wire for power supply to heater. Two tubes of ¼” OD are connected to head for reference gas / air and one for sending zero calibration gases of 1% oxygen.
32. What is the operating principle of portable oxygen analyzer? (E/S)
Answer: It is microfuel (catalytic combustion) cell which change it’s resistance as per concentration of the oxygen presents in the air. Further it is connected to Whetstone Bridge and shows the % of oxygen.
33. Why H2S and Hydrocarbon atmospheric monitors with local as well as central alarm facility are being provided? What are the type of H2S and Hydrocarbon atmospheric sensors available in market? (E/S)
Answer:
In any refinery H2S and Hydrocarbon gases are present in large quantity specially in Crude, SRU and any distillation units, which are harmful for human life as well as equipment / plant. It’s presence shall immediately alert the CCR operator as well as local plant operator. Generally H2S sensors are solid state, adsorption, diffusion type. Hydrocarbon
sensors are Catalytic type.
34. What is RVP? Name one liquid we measure RVP? (S/T)
Answer: RVP (Reid vapor pressure) is the kinetic vapor pressure of a liquid at constant pressure as per ASTM D 323 58. RVP is measure for Light and heavy Naphtha.
35. Name two liquids we measure Distillation. (S)
Answer: We measure the boiling point Kerosene and Diesel.
36. What are types of CO nalyzers are there? Whether the same analyzer can measure CO & O2 in the same unit? (E)
Answer: Non-dispersive infrared (NDRI), Gas Chromatograph, Electro chemical cell and Catalytic Oxidation type detectors can measure CO. Same analyzer can measure O2 & CO by Ametek combined single unit. It use Zirconia probe for oxygen measurement and Catalytic thermostat for CO measurement.
37. What is the relationship between CO & O2 in a furnace / heater? (E)
Answer: Oxygen and Carbon Dioxide concentration is inversely proportional in any Furnace or Heater.
38. What is trimming of O2 in auto combustion loop? (E)
Answer: Optimized % of the Oxygen present in the flue gas of Chimney outlet gives the set point to the Air / Fuel ratio controller of a auto combustion control loop of a furnace or heater.
39. What is engineering unit for Conductivity & Resistivity ? (S/T)
Answer: Conductivity engineering unit will be Mho/cm or Siemens / Cm and the same for Resistivity Ohm/Cm.
40. Why Conductivity of a liquid is measured? What will be normal conductivity of a polisher outlet of a DM Plant? (E)
Answer: Conductivity is measure to get ionic concentration of electrolyte samples. Polisher outlet will be of very ultra pure of less conductivity. It will be in the range of 0 to 0.5 micro mho.
41. What is the difference between flow through and in-situ sensors? (E)
Answer: Flow through sensor is sample is drawn near analyzer with the help of proper sampling unit and the sensor is mounted after the same. In situ sensor is it mounted directed on the process pipe, vessel or duct. In general the in-situ
sensor shall be more rugged.
42. What is Turbidity and what is it’s unit? (E)
Answer: It is the suspended solid present in the water. It’s unit is NTU i.e. Nephelometric Turbidity Unit.
43. What is TDS? What is the relation between TDS and conductivity? (E)
Answer: TDS is total dissolved solid in the water. Practically it is observed that two units of TDS is equal to one unit conductivity.
44. How the Conductivity analyzer calibration can be done? (T/S)
Answer: It can be done through injecting a decade resistance box.
45. What is cell constant? What are the different values of cell constant? (E/S/T)
Answer: Cell constant is the ratio between the length of the probe and the area of cross section of the probe. It can be 0.1, 1.0, 10,
46. What shall be the probe material available in the market and what shall be chosen for acid application? (E/S)
Answer: generally cells are of glass, epoxy and stainless steel, whereas the probes are of platinum, nickel, titanium. Acid application SS316 / Ni electrode shall be chosen.
47. How can you detect the cooling water tube leakage in a condenser from Conductivity reading? (E)
Answer: If the conductivity reading overshoot high, it indicate that cooling water tube leakage has occurred.
48. What is viscosity? How it is related to pressure, flow and temperature? (E)
Answer: It is a property of a fluid which affect it’s behavior. It the consistency of resistance offered by the fluid for it’s deformation. It is related to temperature only.
49. What is dynamic and kinetic iscosity? What are the engineering units of the same? (E)
Answer: Dynamic viscosity is ratio of applied stress to resulting shear velocity. Whereas kinetic viscosity is absolute viscosity divided by density. Engineering unit dynamic viscosity is poise and the same for kinetic viscosity is stoke.
50. What is the UV type and IR type analyzers? (E)
Answer:
UV is Ultraviolet region of the electromagnetic spectrum is generally considered to cover wavelength of 200 to 400 nanometer (nm). IR infrared absorption is a technique that can be used for chemical analysis. The IR region of the electromagnetic spectrum is generally considered to cover wavelength of 0.6 to 1000 μm.

51. Why the CO can not be measured by UV type Analyzer? (E)
Answer: CO spectrum region does not fall in UV region.
52. What is the principle of measuring Silica? Why it is required to be measured? What is the engineering unit of the same? (E/S)
Answer:
Silica can be measured by colorimeter. If the stream will be used for any steam
turbine, the presence of Silica in the steam will reduce the longevity of the
Turbine blade. The engineering unit of the same is PPM or PPB.
53. What are the reagents are used for Silica analyzer of colorimeter type? (E)
Answer: The reagents are Sulfuric acid, ammonium molybdate, oxalic acid, ascorbic acid. Molybdoslilcic acid converts to blue by ascorbic acid. Oxalic acid prevents interference of phosphate.
54. Why the dissolved oxygen is being measured at deaerator O/L? (E)
Answer: The function of any Deaerator is to remove the dissolved oxygen contain in DM water by injecting steam as presence of oxygen help to corrode the steam generator tube. Hence the dissolved oxygen is being measured at deaerator O/L to measure the performance of the Deaerator.
55. Why sample cooler is being used? (S/T)
Answer: Most of the cases the sample (liquid or gases) are in hot phase, where as the detector is suitable at ambient or maximum 70 Deg C. Hence a miniature heat exchanged is used to cool down the sample temperature, which is called Sample cooler.
56. Why the chlorine is dosed in the cooling water or portable water? (E/S)
Answer: Chlorine is dosed to avoid biological and fungal growth in cooling water or portable water.
57. How the Chlorine is being dosed? (S/T)
Answer: Chlorine is dosed through to waterline through Chlorinator, where injector created vacuum and chlorine is drawn from the cylinder.
58. What are the sensors used for Na+ detection? What is the engineering unit for Na+ measurement? (E)
Answer: Measuring electrode is sodium ion responsive electrode and the reference one is calomel. The potential difference between the both is logarithmic with respect to change in sodium ion concentration. The engineering unit for Na+ measurement is μg / Kg.
59. What is the reagent for Na+ measurement and why the same is used? (E)
Answer: he reagent is Ammonia solution. Diethylamine solution (50%) shall be used for measuring concentration bellow 0.1 μg / Kg. It is used for pH balancing/ adjustment at the range of 10.7, which suit to measure sodium ion at the range of 0.5 micro gram per kg.
60. What is the measuring principle of Cl2?(S/T)
Answer: Chlorine can be measured by amperometric probe, which consist of a gas permeable membrane, a gold cathode and a silver anode. Further, the probe shall be filled with salt electrolyte.
61. Where do we measure the SOx & NOx and Why it is required? (E/S)
Answer:
Now a days air pollution is critical anywhere in the world. Hence continuos online Stack / chimney emission has become mandatory. We measure SO2 for SOX and NO / NO2 for Nox.
62. What is the principle of measuring the SOx & NOx? (E/S)
Answer: Infrared (IR) absorption (or reflection for solid) is used for measuring the SOx & NOx .
63. What is thermal conductivity Analyzer and which is the application? (E/S)
Answer: Catalytic-coating thermister beading get heated proportional to the concentration of sample and this change in resistance is sense by Wheatstone Bridge. It is used as Hydrogen Analyzer.
64. What is Air demand analyzer? What are the components are being measured in which principle? What are the different blocks of the same? (E)
Answer: It is an analyzer used to assist in the control of the combustion air to acid gas ratio in Calus Sulfur recovery plant. It is photometric analyzer of adsorption type. SO2 and H2S are being measured in this analyzer. It has got probe with heater, sampling oven (Sample shut off valve, Sulfur knock out unit, sample cell, sample drive
aspirator, zero & purge unit), Detector (Source, Chopper motor with wheel, opto isolator, PMT), Analyzer (RCS (Remote Control Station), LCS (Local Control Station), Temperature controller, Signal isolator cum converter unit).
65. Which plant Air demand analyzer is being used? What is the recommended set temperature of the probe heater? (S)
Answer: Air demand analyzer is used in the Sulfur Recovery Unit (SRU). The probe heater shall be maintained at 130 ˚C. That is melting point of Sulfur.
66. What is Bougier’s Law and Beer Lambart Law? Where it is used? (E)
Answer:
ams2001glos-Be18
I = Transmitted Radiation Intensity
IO Incident Radiation Intensity and τ is the pathlength
Log (t) = μ l (Where μ is Linear absorption coefficient and
l is thickness of absorber). Air Demand analyzer is based on this Principle.
67. Which plant we generally use moisture analyzers and what are types of moisture analyzer are generally available in the market? (S/E)
Answer: Moisture analyzer is used in the Instrument Air unit after air dryer. Two types are popular, they are Thin film
capacitance (Aluminum Oxide or Polymer) and Lithium Chloride Saturated salt due point sensor.
68. What is a grab sample point? (T)
Answer: It is sample points with all sample conditioner unit like sample cooler, Pressure regulating valve, temperature shut off valve, rota meter, pressure gauge, Temperature gauge.
69. What is auto sampler and what is the application of the same? (S/T)
Answer: It is Peristaltic Pump or Solenoid operated valves, which operated in some prefixed time interval to gathered sample (Liquid) in a container. It is being analysis at Lab.
70. What is an analyzer shelter? Why is the same required? (T)
Answer: It is PVC air conditioned room where all of the field analyzers are located mainly which are microprocessor based like Gas Chromatograph or other electronics analyzer control unit which are sensitive to high temperature.
71. In normal application when any analyzer is connected to DCS, it will be loop powered or self powered? (E)
Answer: It will be self-powered. Most of the cases Analyzer have it’s own power supply unit.
72. What is chopper motor? (T)
Answer: The motor connected to the chopper wheel of any UV detector is called chopper motor.
73. What  is a Drager tube and what is the application of the same? (E/S)
Answer: It is tube packed with chemical used to measure the concentration of H2S and SO2. PPM or % levels
of gas concentration are marked on the tube. Drager is a trade name.
74. What material shall be used for seawater application Monel, Inconnel, SS 316, CS? (E)
        Answer: Monel
75. What will be calibration gas span for a SO2 analyzer range of 0- 500 PPM? (S/T)
Answer: Span gas will be 400 ± 1% of SO2 and  balance Nitrogen. The zero gas will be Air or Nitrogen.
76. Why calibration and normal switch is provided for any analyzer? (S/T)
Answer: It is switch located in the field, which indicates the analyzer, is in normal operation or
calibration is in progress. It is required for panel operator guidance.
77.  What is a Z purged and X purged? (E)
Answer: Z purged is called the process, which reduced internal enclosure area division rating from Division 2 to non-hazardous area. Y Purged is called the process, which reduced internal enclosure area division rating from Division 1 to Division 2.
78. What is a normal accuracy of a SO2 and Oxygen analyzer? (S/E)
Answer: Normal Accuracy of SO2 analyzer is ± 2% Normal  Accuracy of Oxygen analyzer is ± 1%
79. What are IP and NEMA standards? ( E/S)
Answer: IP stands for Ingress Protection and NEMA is stand for National Electrical Manufacturer Association. These standards are used for the protection class against dirt, water jet, etc. of any enclosure.
80. What is cross sensitivity? (E)
Answer: In IR method of analysis cross sensitivity is the common problem. Cross sensitivity is that more than one  gaseous component absorbs the radiation at a selected wavelength, which affect the accuracy of measurement. Water vapor and Carbon dioxide are common component, which cause the cross sensitivity.
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