1. TELEVISION CAMERA TUBES
TOPIC
TELEVISION CAMERA TUBES
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

2. OUTLINE OF LECTURE CAMERA TUBES BASIC PRINCIPLE TYPES OF CAMERA TUBES
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

3. TELEVISION CAMERA TUBES
An electron tube use a light-sensitive material/receptor that converts an optical image into an electrical television video signal.
The tube is used in a television camera to generate a train of electrical pulses representing the light intensities present in an optical image focused on the tube.
Each point of this image is interrogated in its proper turn by the beam in tube , and an electrical signal corresponding to the amount of light at that point of the optical image is generated by the tube. This signal represents the video or picture portion of a television signal.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

4. BASIC PRINCIPLE Photoconductive effect Photoemission effect
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

5. Photoemission principle
Certain metals emit electrons when light falls on their surface.
These emitted electrons are called photoelectrons and the emitting surface a photocathode.
Light consists of small bundles of energy called photons.
When light incident on a photocathode ,the photons give away their energy to the outer valence electrons to allow them to overcome the potential energy barrier at the surface.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

6. The number of electrons which can overcome the potential barrier and get emitted ,depend on the light.
Alkali metal are used as photocathode because they have very low work function.
Cesium silver / bismuth silver cesium oxides are preferred as cathode surface because they are sensitive to incandescent light and have spectral response very close to the human eye.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

7. Photoconductive principle
In some metal , when light photon fall on it then its conductivity / resistivity change.
Semiconductor metals like selenium, tellurium and lead with their oxide have this property known as photoconductivity.
The variation of resistance at each point across the surface of the material is utilized to develop a varying signal by scanning it uniformly with an electron beam.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

8. Types of Camera Tubes Image Orthicon tube Vidicon Plumbicon
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

9. Image Orthicon tube
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

10. Principle : Photoemissive It has three section: Image section
Image Orthicon tube
Principle : Photoemissive
It has three section:
Image section
Scanning section
Electron gun –cum-multiplier section
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

11. Image section
Glass plate : coated with Silver-antimony serve as photocathode
Lens assembly : light from the scene to be televised is focused on the photocathode surface by lens system
Photocathode surface is semitransparent and light rays penetrate it to reach its inner surface where electron emission takes place .
Target plate : when electron emit from cathode ,it can not store charge being a conductor .
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

12. For this reason the electron image is made to move towards the target plate located at short distance from it.
The target plate is made of a very thin sheet of glass and can store charge received by it. This is maintained at about 400v more +ve w.r.t photocathode
When electron move from cathode to target plate there is chance that it may repel each other ,this can result in distortion of the information available as charge image.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

13. To prevent this divergence effect an axial magnetic field generated by focus is employed
This magnetic field impart helical motion to electrons and focus them on target plate .
The image side of target plate has coating of cesium that emit secondary electron.these secondary electron is collected by wire mesh which is located at front of target plate .
The +ve charge appeared on target plate is proportional to light intensity distribution on photocathode
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

14. Scanning section Fine electron beam Focus ,alignment coil
Deflection coil
1. Horizontal deflection
2. Vertical deflection
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

15. Electron gun assembly and multiplier
Multistage electron multiplier
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

16. Vidicon Principle : Photoconductive It has three section:
Target section
Scanning section
Electron gun
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

17. Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

18. Target section Glass plate Lens assembly Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

19. Scanning section Fine electron beam Focus ,alignment coil
Deflection coil
1. Horizontal deflection
2. Vertical deflection
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

20. Electron gun assembly Electron gun Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

21. Principle of operation
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

22. Application of vidicon
Close circuit TV system
Earlier type of vidicon were used only where there was no fast movement , because of inherent lag
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

23. Plumbicon Camera Tube lower image lag.
It has fast response and produce high quality pictures at low light level.
It has small size and light weight and has low power operating characteristics .
It is similar to vidicon tube except small change in target plate
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

24. Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

25. Target plate n-type layer sno2 p type layer PbO Scanning beam Light
Glass face plate
p type layer PbO
Scanning beam
Light
Intrinsic layer
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

26. Plan of a colour television camera showing generation of colour signals and Y matrix for obtaining the luminance (brightness) signal.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

27. Figure shows a simple block schematic of a colour TV camera
Figure shows a simple block schematic of a colour TV camera. It essentially consists of three camera tubes in which each tube receives selectively filtered primary colours. Each camera tube develops a signal voltage proportional to the respective colour intensity received by it.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

28. Light from the scene is processed by the objective lens system.
The image formed by the lens is split into three images by means of glass prisms.
These prisms are designed as diachroic mirrors.
A diachroic mirror passes one wavelength and rejects other wavelengths (colours of light).
Thus red, green, and blue colour images are formed.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

29. The rays from each of the light splitters also pass through colour filters called trimming filters.
These filters provide highly precise primary colour images which are converted into video signals by image-orthicon or vidicon
camera tubes.
Thus the three colour signals are generated. These are called Red (R), Green (G) and Blue (B) signals.
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society

30. THANKS
Akshay Jilowa GPCG Jalandhar
Punjab EDUSAT Society