Radar Interview Questions & Answers

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Radar Interview Questions

    1. Question 1. What Are The Basic Factors With Which The Tv System Must Deal For Successful Transmission And Reception Of Picture?

      Answer :

      • Gross structure
      • Image continuity
      • No of scanning lines
      • Flicker
      • Fine structure
      • Total degradation

    2. Question 2. What Is Vertical Scanning?

      Answer :

      It is the movement of electron beam spot in the vertical direction.

    3. Question 3. What Is Raster?

      Answer :

      Raster is the scan pattern in which an area is scanned from side lines from top to bottom.

    4. Question 4. What Is Scanning?

      Answer :

      Scanning is the process by which an electron beam spots a mode to move across a rectangular area so as to cover it completely.

    5. Question 5. What Is Horizontal Scanning?

      Answer :

      The movement of electron beam spot from left to right and back so as to start a new line in same direction is termed as horizontal scanning.

    6. Question 6. What Is Video Signal?

      Answer :

      The time varying electrical signal voltage obtained from the TV camera tube circuit representing the special distribution of brightness of the image is called video signal.

    7. Question 7. What Are The Uses Of Radar?

      Answer :

      Detection and Search Radar: Radar is basically used in detection purpose in military and coastal surveillance which help the people in detecting the harmful objects coming towards them.

      Missile guidance system: Nowadays, this radar has become quite popular in missile guidance as it helps the people in knowing where to launch the missile or where to land it etc.

      Air Traffic control: In foreign countries, the traffic is being controlled through the use of radar.

      Weather Forecasting: This is quiet helpful in weather forecasting as it helps in detecting the temperature of climate or when will the rainfall occurs.

    8. Question 8. What Is Doppler Effect?

      Answer :

      The sudden change in pitch of a car horn as a car passes by (source motion) or in the pitch of a boom box on the sidewalk as you drive by in your car (observer motion) was first explained in 1842 by Christian Doppler. His Doppler Effect is the shift in frequency and wavelength of waves which results from a source moving with respect to the medium, a receiver moving with respect to the medium, or even a moving medium.

      Although first discovered for sound waves, the Doppler effect holds true for all types of waves including light (and other electromagnetic waves). The Doppler Effect for light waves is usually described in terms of colors rather than frequency. A red shift occurs when the source and observer are moving away from each other, and a blue shift occurs when the source and observer are moving towards each other. The red shift of light from remote galaxies is proof that the universe is expanding.

    9. Question 9. What Are The Factors That Affect Radar Performance?

      Answer :

      The performance of a radar system can be judged by the following:

      1. The maximum range at which it can see a target of a specified size.
      2. The accuracy of its measurement of target location in range and angle.
      3. Its ability to distinguish one target from another.
      4. Its ability to detect the desired target echo when masked by large clutter echoes, unintentional interfering signals from other “friendly” transmitters, or intentional radiation from hostile jamming (if a military radar).
      5. Its ability to recognize the type of target.
      6. Its availability reliability, and maintainability.

    10. Question 10. Why Flicker Is Not Removed By Progressive Scanning?

      Answer :

      Flicker can be removed by doubling the speed of progressive scanning, but doubling the speed will double the band-width, which is not desirable.

    11. Question 11. Why Is Retrace Blanked?

      Answer :

      Retrace his blanked because of the retrace is visible on the screen, it will cause distortion in the picture.

    12. Question 12. What Is Kell Factor (k)?

      Answer :

      The kell factor (k) or the resolution factor gives the effective number of horizontal scanning lines can be scanned because of practical limitation. The value of kell factor lies between 0.65 to 0.75.

    13. Question 13. What Is Importance Of Back Porch?

      Answer :

      Back porch absorbs ringing oscillations due to fly-back. In the absence of the back porch, these oscillations would have distorted the video signal.

    14. Question 14. Which Principles Are Used For Optical Electrical Conversion?

      Answer :

      Two basic principles are used for optical electrical conversion. They are based on photo electric effect.

      The two principles are: 

      1. Photoemission.
      2. Photo conduction.

    15. Question 15. List 4 Merits Of Digital Tv Receivers?

      Answer :

      Reduced ghosts. Reduced of 50 HZ flicker. High resolution pictures. Slow motion action.

    16. Question 16. Write Short Notes On Video Disc System?

      Answer :

      The video disc is essential a gramophone record with pictures on it. The first video disc was the laser optical and second video disc system is based on the capacitance principle.

    17. Question 17. Why Do Blind Speeds Occur?

      Answer :

      Blind speeds occur because of the samples nature of the pulse radar wave form. Thus it is sampling that is the cause of ambiguities or aliasing in the measurement of the Doppler frequency.

    18. Question 18. What Do You Mean By Longitudinal Video Recording?

      Answer :

      A method in which video signals are recorded on at least several tracks along the length of the tape.

    19. Question 19. What Are The Two Types Of Video Disc System?

      Answer :

      Laser or optical disc system. Capacitance disc system.

    20. Question 20. What Is The Function Of Tv Camera Tube? What Are The Major Problem Occurring During The Conversion Of Optical To Electrical Signal In Tv Camera?

      Answer :

      • Heart of a TV camera is a camera tube.
      • Camera tube –converts optical information into electrical signal.
      • Amplitude proportional to brightness.
      • Optical image is focused by a lens assembly to a rectangular glass face –plate.
      • Transparent conductive coating at the inner side of the glass faces plate.
      • On which is laid a thin layer of photo conductive material having a very high resistance when no light falls on it.
      • Resistance decreases when the intensity increases.
      • Electron beam –used to pick up the picture information available on the target plate in terms of varying resistance.

      Beam is formed by an electron gun:

      • Deflection coils are fed separately from two oscillators-continuously generates saw tooth wave forms having different desired frequency uses magnetic deflection.
      • Deflection by first coil-horizontal motion of beams and then brings quickly to left side to commence the trace of next line.
      • Deflection by second coil-Vertical motion and its quick retrace back to the top to start the process allover again.
      • Encounters different resistance across the target plate.
      • Result in a flow of current which varies in magnitude during scanning.

      We get the true information of the scene:

      • Scanning converts the in antenna formation existing in space and time coordinates into time variation only –called a video signal.
      • Video signal is amplified-amplitude modulated with channel picture carrier frequency.

      The major problems during this conversion are:

      • Poor sensitivity.
      • Poor resolution.
      • Higher noise level.
      • Improper spectral response.
      • Instability.
      • Poor contrast range.
      • Difficulties in processing the output signal.

    21. Question 21. Explain How The Image Orthicon Develops Video Signal When Light From Any Scene Is Focused On Its Face Plate?

      Answer :

      It was first produced in the year 1945 and because of its superior performance it’s soon replaced all earlier tv camera tube like image dissector, iconoscope   and orthicon. 

      It has the following qualities: 

      • It has high photo graphic sensitivity. 
      • It provides a very dependable service. 
      • It provides an excellent response over a wide. 

      Range of illumination level varying from bright sunlight to dark shadow. As a result of this, image orthicon remained in popular TV studio use for a long period but it is now being replaced by plumb icon.

      Principle of working:

      • A lens system focuses light from the scene on to a translucent photo cathode.
      • Electrons gate emitted from the various points on photocathode surface in proportion to the illumination .
      • These photo electrons travel to a thin glass target causing secondary emission from it.
      • These secondary electrons get collected by a fine mesh placed close to the glass target plate as shown fig.
      • This causes electron deficiency distribution or positive charge distribution on the photo cathode.
      • This positive charge distribution originally on the front surface of the target plate leaks through thin plate to the back surface.
      • A low velocity scanning beam from an electron at the other end of the image orthicon tube scans the back surface of the target plate following a predetermined scanning pattern.
      • The electroned is slowed down to a non zero velocity as it approaches the target.

      From a dark element ,the scanning electron beam is returned  unaffected .However ,at light element(positively  charge element),the scanning beam is deprived of some of its electrons to netralise the positive charge so that the returning electrons to neutralize the positive charge so that the returning electron beam contains lesser electron .This varying density  returning beam  is fed to an electron multiplier.

    22. Question 22. What Is The Principle Of Operation Of Guided Wave Radar?

      Answer :

      • Radar level measurement technology can be broken down into two different categories; Pulsed and Frequency Modulated Continuous Wave (FMCW).
      • An advantage with Pulsed Technology is that it requires less processing power. Therefore most two-wire gauges use this technology.
      • An advantage with FMCW is that higher accuracy can be achieved but more processing power is required and therefore FMCW-radars are typically four-wire.
      • In Pulsed transmitters the level measurement is a function of the time taken from the radar signal to travel to the surface and back.
      • In FMCW gauges the transmitter constantly emits a swept frequency and the distance is calculated by the difference in frequency of emitted and received signal.

    23. Question 23. Are Radar Gauges Safe?

      Answer :

      Yes. The emitted signal is less than three percent of maximum leakage allowed from a microwave oven. Radar waves are of no greater intensity than the constant radio, cellular and other communication waves that surround us every day.

      Furthermore the transmitter is normally placed in a metallic tank that acts as a Faraday’s cage and therefore the radar waves are isolated within the tank.

    24. Question 24. What Is The Difference In Frequency Between Pulsed Technology Guided Wave Radar And Non Contacting Radar?

      Answer :

      With Guided Wave Radar the pulsed microwave are guided down the tank by the probe, making it less sensitive to disturbances than free propagating microwaves.

      Pulsed Non Contacting Radar uses a carrier frequency, e.g. 6 Hz or 26 Hz, to carry the microwaves which are radiated into the tank with an antenna.

    25. Question 25. Why Should We Use Radar Technology?

      Answer :

      The radar signal is virtually unaffected by the tank content and tank atmosphere, temperature or pressure. The measurement is not influenced by changing material characteristics such as density, dielectric properties and viscosity.

      Since there are no moving parts the transmitters are virtually maintenance free. All of the characteristics above make radar a very useful and fast growing level measurement technology.

    26. Question 26. How Does The Frequency Of The Radar Affect The Measurement?

      Answer :

      A higher frequency provides a more concentrated narrow beam which can be useful in applications where there are obstacles present in the tank such as many-ways, agitators or heating coils.

      The downside of high frequency is that the measurement is more affected by vapers, dust and product build up on the antenna, Low frequency radar which has a longer wavelength and wider beam angle, tends to cope better with steam, dust, condensation, contamination and turbulent surfaces.

    27. Question 27. In What Way Does The Dielectric Constant (dc) Of The Media Affect The Measurement?

      Answer :

      • Electromagnetic energy is emitted from all radar devices. When the emitted signal reaches a point where there is a change in DC, usually the media surface, some of the signal is reflected back to the transmitter.
      • The amount of energy that is reflected back to the transmitter is proportional to the DC of the media. A rule-of-thumb is that the value of the dielectric constant represents the percentage of energy that is reflected.
      • Thus a DC of eight means that eight percent of the emitted energy is reflected back to the transmitter. Fundamentally media with a higher DC provide stronger return signals and are therefore easier to measure.

    28. Question 28. Does Radar Work On Foam?

      Answer :

      • The effects of foam on a radar measurement can be difficult to predict. In some applications the foam may dampen out the signal completely while other types of foam may be transparent to the transmitter.
      • The thickness, density and the dielectric constant are factors that need to be considered when evaluating an application with foam.
      • On dry foam the microwaves typically passes through and detects the liquid surface below. On medium type foam the signal can be absorbed or scattered and the results are therefore hard to predict.
      • If the foam is wet the microwaves are often reflected from the foam surface and thereby the foam surface level is measured.
      • The frequency at which the radar operates also affects how foam is measured. Low frequency radar (5 GHz) in general penetrates foam to a larger extent than high frequency (20 GHz) radar.
      • Guided Wave Radar is in general better suited to measure on applications where foam is present, since the radar uses a lower frequency pulse.

    29. Question 29. Are There Any Restrictions On What Still-pipe Material Can Be Used?

      Answer :

      Any type of conductive material can be used as long as it is compatible with the process media.

      If the material is not conductive it will be transparent to the radar-beams and therefore it will have no effect.

    30. Question 30. Will Two Or More Radar Units In One Vessel Conflict With Each Other?

      Answer :

      The signals from two or more transmitters in one tank will not blend and therefore the radar units will not conflict with each other.

      If it concerns two or more 3300s the rules for nearby objects would apply to the probes as they do to other metallic objects nearby. For that reason the probes need to be installed a certain distance away from each other.

    31. Question 31. Will Radio Noise Or Other Interference Cause Problems?

      Answer :

      The transmitters use a specific narrow frequency and are therefore not prone to disturbances from other sources.

      It is very uncommon with disturbances and it is rare that the disturbance source operates at precisely the same frequency as the transmitter.

      Furthermore, the transmitters are often installed in metallic tanks that provide a Faraday’s cage which prevents electromagnetic disturbances from the outside to enter the tank. With Guided Wave Radar, if disturbances are present in tank the coaxial probe are recommended, since the radar signal travels inside of the pipe undisturbed by the interference sources on the outside.

    32. Question 32. Are There Any Restrictions On The Nozzle Height?

      Answer :

      Since the nozzle, and especially the lower end of the nozzle, can create interfering echoes it is recommended that the height of the nozzle is kept within certain values depending on the type of probe / antenna and type of transmitter that is used.

    33. Question 33. Are There Any Restrictions On The Nozzle Diameter?

      Answer :

      In conjunction with the above statement, the nozzle diameter also affects the measurement.

      Since a diameter nozzle that is too small will create disturbance echoes.

    34. Question 34. Are There Any Restrictions When Measuring In Stilling Pipes?

      Answer :

      Pipes should be an all-metal material. Non-metallic pipes or sections are not recommended for non-contacting radar.

      Plastic, Plexiglas, or other non-metal materials do not shield the radar from outside disturbances and offer minimal, if any, application benefit.

      Other requirements include:

      • Pipe should have a constant inside diameter
      • Pipe must be smooth on the inside (smooth pipe joints are acceptable, but may reduce accuracy)
      • Avoid deposits, rust, gaps and slots
      • One hole above the product surface
      • Minimum whole diameter is 0.25 in. (6 mm)
      • Whole diameter (Ø) should not exceed 10% of the pipe diameter (D)
      • Minimum distance between holes is 6 in. (150 mm) (1)
      • Holes should be drilled on one side and de-burred
      • Ball valve or other full valves must be completely open

      Failure to follow these requirements may affect the reliability of the level measurement.

    35. Question 35. What Is Purpose Of Exotic Materials?

      Answer :

      In some applications with high temperatures, or in highly corrosive environment, the probes or antennas need to be made out of exotic materials that can be stand the material stress.

      Two different exotic materials as standards: Alloy 400 C-276

    36. Question 36. What Is Eddl & Dd’s? And How Do They Affect Configuration Tools And Host Systems?

      Answer :

      • Basic configuration can easily be done either with Rosemount Radar Master, a Rosemount 375 Field Communicator, the AMS™ Suite, DeltaV® or any other DD (Device Description) compatible host system.
      • For advanced configuration features and extensive diagnostics, Radar Master, or an alternative host that supports enhanced EDDL (such as the AMS Device Manager) is required.
      • Rosemount Radar Master is shipped with every transmitter but it is also possible to download Radar Master or other DD’s on Rosemount.com Radar Master is a user-friendly, Windows based software package that provides easy configuration and service for both FOUDATION™ fieldbus and HART®.
      • A wizard guides the user to enter the required parameters for a basic configuration. “Measure & learn” functionality is accessed through Radar master. It enables automatic suggestion of level threshold values, thereby making tough applications easy to configure.
      • Radar Master also includes an echo curve with movie feature, off-line configuration, logging and extensive on-line help. The Enhanced EDDL capabilities of the Rosemount Radars also make it possible to view the echo curve from a field communicator or AMS, and to initiate the Measure-and-Learn functionality in the transmitter.

    37. Question 37. How Will Coating Affect The Measurement?

      Answer :

      If coating forms on the probe the measured signal will be weaker. If the media itself has a high dielectric constant some coating is not much concern but if it is a low DC media coating can be a problem.

      If a twin probe or a coaxial probe is used the coating can cause bridging between the two leads and this will create false echoes that can lead the transmitter to interpret a bridge as the actual level.

      Single lead is recommended in coating applications. Coating can cause an accuracy influence. Maximum error due to coating is 1-10% depending on probe type, dielectric constant, coating thickness and coating height above product surface.

    38. Question 38. What Are The Special Considerations For Interface Measurement?

      Answer :

      For interface measurement a few criteria have to be fulfilled:

      • The dielectric of the upper product must be known and should not vary.
      • Upper product dielectric < Lower product dielectric.
      • Difference between dielectrics depends on the upper product thickness, but a guideline is > 10(3300) > 6(5300).
      • Thickness of upper product > 10 cm (4 in.) for coax, rigid twin and rigid single probes and 20 cm (8 in) for flexible twin probes in order to be detected.
      • The max measuring range is limited by the upper product dielectric constant.
      • Coaxial, Twin probes or rigid single can be used.
      • Max upper product DC is 5 for twin lead probes and 10 for coaxial probe.

      Target applications include interfaces between oil/oil-like (DC < 3) and water/water-like liquids (DC > 20). Consult factory regarding other interface applications and when emulsion layer!

    39. Question 39. Can Guided Wave Radar Measure Emulsion Layers?

      Answer :

      Emulsion layers are in general hard to predict and there are three main types of layers:

      • DC of top layer and emulsion layer is similar (difference in dielectric constant < 10). In this case the interface level as reported by the transmitter will be the bottom of the emulsion layer.
      • DC of bottom layer and emulsion layer is similar (difference in dielectric constant between top layer and emulsion layer > 10). In this case the interface level as reported by the transmitter will be the top of the emulsion layer.
      • There is a linear transition in DC from the bottom to the top of the emulsion layer. In this case it is hard to predict where the reported interface level is. If the linear transition is over a long distance there is a risk that no interface echo is reflected back to the transmitter.
      • Since the reflecting pulse is created when there is a distinct change in DC. If a linear oil water interface is very thin (< 10 cm) the transmitter would probably give a good signal from the interface since the emulsion is so thin and the difference in dielectrics between oil and water is large.
      • It is difficult to say though where the transmitter will report the interface level. It can report the top of, the bottom of, or somewhere within, the emulsion layer.

    40. Question 40. Will The Guided Wave Radar See Sand In The Bottom Of A Vessel?

      Answer :

      No. Since the sand will be embedded in water which is a high dielectric media (DC~80) the transmitter will only see the water.

      The same is true for all media that are embedded in water.

    41. Question 41. Is There Any Inactive Part Of The Probe?

      Answer :

      The active measuring range is reduced by the upper and lower dead zones. The upper dead zone is the minimum distance from the reference point to the product surface.

      The measuring range is also reduced in the end of the probe by the lower dead zone.

      How large the upper and lower dead zones are depend on probe type and the dielectric constant of the measured media.

    42. Question 42. How Close To The Tank Wall Can The Probe Is Mounted?

      Answer :

      Like the nozzle the tank wall can also affect the measurement through disturbance echoes.

      The minimum distance to the tank wall is the same as the distance to any disturbing object that may be present in the tank.

      If there are obstacles present in the tank the coaxial probe is the best probe to use. If the tank wall is metallic and smooth the probe can be mounted closer to the wall.

    43. Question 43. What Pull Force Will Break A Flexible Single Lead Probe?

      Answer :

      • In solid application, media might cause down-pull forces on silo roofs. The silo roof must be able to withstand the probe collapse load or at least the maximum probe tensile load.
      • The tensile load depends on the silo size, material density, and the friction coefficient. Forces increase with the buried length, the silo and probe diameter.
      • In critical cases, such as for products with a risk for build-up, it is better to use a 0.24 in (6 mm) probe.
      • Depending on their position, forces on probes are generally two or ten times greater on probes with tie-down than on probes with ballast weights.

    44. Question 44. What Is The Principle Of Operation For Non Contacting Radar?

      Answer :

      • FMCW technology transmitter constantly emits a swept frequency signal and the distance is calculated by the difference in frequency between the emitted and received signal at any point in time.
      • One advantage with FMCW is that higher accuracy can be achieved.
      • The Pulsed Radar transmitter is free propagating radar. The level of the liquid is measured by short radar pulses which are transmitted from the antenna at the tank top towards the liquid.
      • When a radar pulse reaches a media with a different dielectric constant, part of the energy is reflected back to the transmitter.
      • The time difference between the transmitted and the reflected pulse is proportional to the distance, from which the level is calculated.

    45. Question 45. How Close To The Tank Wall Can The Non Contacting Transmitter Is Mounted?

      Answer :

      The minimum distance to the tank wall depends on which antenna is used. With a more concentrated beam (larger antenna), the closer to the tank wall the device can be mounted.

    46. Question 46. What Are The Special Considerations When Measuring Ammonia?

      Answer :

      Tanks with anhydrous ammonia have a heavy vapor above the surface that attenuates the signal from the radar transmitter. A higher pressure in the tank will cause a more attenuated signal.

      A special formula is therefore used to evaluate what the maximum measuring range is in anhydrous ammonia as a function of the pressure in the tank.

      For the 5600 the formula is:

      Max Measuring Range (m) = 20 / Pressure in Bar

      Note that, when measuring anhydrous (aqueous) ammonia, this formula does not apply. Hydrous ammonia has a high dielectric constant and therefore provides good reflection.

    47. Question 47. Why Do You Use Process Seal Antennas?

      Answer :

      To isolate electronics from process in tank such as vapour and corrosion. The Process Seal antenna has a PTFE window. It is an all PTFE antenna (all materials exposed to tank atmosphere are PTFE).

      Due to the smooth surface of the window and the non-sticky nature of PTFE it can be used on some hygienic applications.

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