Phototube

Source: Wikipedia, the free encyclopedia.
Two different types of phototubes

A phototube or photoelectric cell is a type of

photoconductive cells. Phototubes were previously more widely used but are now replaced in many applications by solid state photodetectors. The photomultiplier tube
is one of the most sensitive light detectors, and is still widely used in physics research.

Operating principles

Phototubes operate according to the

The light wavelength range over which the device is sensitive depends on the material used for the photoemissive cathode. A caesium-antimony cathode gives a device that is very sensitive in the violet to ultra-violet region with sensitivity falling off to blindness to red light. Caesium on oxidised silver gives a cathode that is most sensitive to infra-red to red light, falling off towards blue, where the sensitivity is low but not zero.[2]

Vacuum devices have a near constant anode current for a given level of illumination relative to anode voltage. Gas-filled devices are more sensitive, but the frequency response to modulated illumination falls off at lower frequencies compared to the vacuum devices. The frequency response of vacuum devices is generally limited by the transit time of the electrons from cathode to anode.

Applications

One major application of the phototube was the reading of optical sound tracks for projected films. Phototubes were used in a variety of light-sensing applications[3] until some were superseded by photoresistors and photodiodes.

References

  1. ^ J.B. Calvert (2002-01-16). "Electronics 30 - Phototubes". University of Denver. Archived from the original on 2006-01-15.
  2. ^ Mullard Technical Handbook Volume 4 Section 4:Photoemissive Cells (1960 Edition)
  3. ^ Bruno, O (2001). "Phototube sensor for monitoring the quality of current collection on overhead electrified railways". Journal of Rail and Rapid Transit. 215 (3): 231–241. Retrieved 11 May 2023.