Television Camera Tube Viva Questions
Television Camera Tube Viva Questions, Viva Questions on Television Camera Tube, TV Camera Tube Viva Questions, Plumbicon Camera Tube Viva Questions, Image Orthicon Camera Tube Viva Questions, Vidicon Camera Tube Viva Questions, Engineering Viva Questions, Television Camera Tube Viva Questions
Short-answer Questions
Q.1. What is a charge image?
Ans. Charge image is a variation of charge from point to point on the surface of the target of a camera tube proportionate to the intensity of light varying from pixel to pixel in a picture.
Q.2. Why is the sensitivity of image orthicon the highest?
Ans. Image orthicon multiplies the number of electrons by secondary emission.
Q.3. Why does vidicon give rise to severe image lag (X-ray effect)?
Ans. Severe image lag in vidicon is due to slow migration of electrons from the target plate when bright light is incident on it.
Q.4. Why is plumbicon’s spectral response poor for red colour?
Ans. Plumbicon uses lead oxide as a target whose surface reflects red light.
Q.5. How does saticon improve the spectral response for red?
Ans. The tellurium used in the target has a high sensitivity for a red light.
Q.6. What is the improvement caused by newvicon camera tube?
Ans. Newvicon has the highest sensitivity of all photoconduction type camera tubes and has a good response in the infrared region.
Q.7. What is a potential well? How is a charge image formed in CCD?
Ans. A potential well is a charge stored in a MOS capacitor formed in a photodiode. The greater the intensity of the incident light falling on the photodiode, the greater is the charge stored in the potential well. Thus each potential well is the replica of light intensity on the corresponding pixel in the picture.
Q.8. How is a charge image scanned in a solid-state camera?
Ans. During the vertical blanking period, the charge stored in MOS capacitors is transferred to vertical shift registers. During the horizontal blanking period, vertical registers in a row transfer their charges to the next lower row. The lowest row’s charge comes to the horizontal shift registers.
Thus during each H-blanking, rows of charges come to the H-shift register in sequence, one after the other every 64 µs. The horizontal trace transfers the charges of each row to a load resistor in sequence. When all the rows have been emptied, the next vertical blanking starts the process again.
Q.9. What are the advantages of a solid-state camera tube over vidicon?
Ans. Advantages of solid-state TV camera are:
- Light weight, small size, highly portable.
- Low voltages.
- No geometric distortion.
- High resolution.
- No image lag.
- Digital output resulting in all the advantages of digital processing of signals.
Q.10. Why cannot photoconduction tubes be used as night vision cameras?
Ans. Photoconduction tubes require visible light for operation. They are not sensitive to heat and hence the set up, if used, will involve a high cost.
Q.11. What are the advantages of the Vidicon Camera Tube?
Ans. Advantages of Vidicon Camera Tube:
- Light and hence portable.
- Signal to noise ratio better than image orthicon.
- No ghost image, no halo.
- Resolution is better than image orthicon.
- Spectral response is close to that of the eyes.
- Sensitivity can he adjusted by changing the target voltage as per illumination of the scene.
- No gamma correction is needed.
Q.12. What are the disadvantages of Vidicon Camera Tube?
Ans. Disadvantages of Vidicon Camera Tube:
- Sensitivity, although quite good, is less than that of the image orthicon.
- Image lag is severe. In extreme cases, even burn-in of the image may occur.
- Dark current (20 nA) is high as compared to other camera tubes.
Q.13. What are the applications of Vidicon Camera Tube?
Ans. Applications of Vidicon: Vidicon camera tube is widely used for outdoor recording, domestic recording, and industrial recording.
Q.14. What are the advantages of the Plumbicon Camera Tube?
Ans. Advantages of Plumbicon camera tube:
- Sensitivity is 400 pA per lumen which is more than that of Vidicon (125 pA per lumen).
- Signal to noise ratio is 47 dB which is more than that of Vidicon (45 dB).
- Image lag negligible.
- Absence of ghost image.
- Dark current about 1 nA, much less than that of Vidicon (20 nA).
- Resolution 50% at 400 lines (5 MHz bandwidth).
- Linearity in conversion of light variation into video.
- Size much smaller than image orthicon.
Q.15. What are the disadvantages of Plumbicon Camera Tube?
Ans. Disadvantages of Plumbicon camera tube:
- Sensitivity is less than that of image orthicon.
- Halo occurs and therefore an antihalo disc has to be used.
- Spectral response is poor in red. Red light is reflected from the target and hence it does not contribute fully to the signal output.
- Size is bigger than Vidicon.
- Gamma being unity, the tube requires gamma correction to offset the gamma effect in the picture tubes.
- Resolution is a bit worse than Vidicon due to scattering of light within the thicker target.
Q.16. What are the applications of Plumbicon Camera Tube?
Ans. Applications of Plumbicon Camera Tube: It is used in the studio as well as outdoor shooting. It is specially stilted to color TV due to the absence of image lag.