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P4221 & P4228

The P4221 was the first firefighting camera built for UK Home Office to exploit the ability of thermal radiation (8 - 14 m) to penetrate smoke. Prior to this the EEV Pevicon tube was more of a laboratory curiosity. for scientific uses needing detection of 8 - 14m infrared
The P4228 production version was used mainly by NATO navies following the HMS Sheffield fire in the Falklands war. Civil deployment was quite limited with cameras seen as specialist equipment. The cameras came to public attention when used at the Putney gas explosion in London 1985. Although the main use to firefighters was to find a safe path or casulaties in thick smoke, the Putney conditions of cold dry weather were favourable for finding heat from buried casualties.


P4228 in training use with Royal Navy  P4228 in training use with Royal Navy

For the hobby user exploring these cameras Pan or Chop mode may be a mystery. The natural behaviour of the sensor material is that it only responds to changes in temperature. In Pan mode the user is required to move the camera to obtain an image.
Chop mode uses a rotating helix shutter rotating at video rate to provide a frame locked image change. By selecting inverted video on the 'chopper closed' image fields this provided an image where white=hot, but also inverted the tube background patterning. Later models of P4228, and also all later tube cameras, included a digital video field store to add the images and cancel out the tube background patterning.


Data Table for P4221 / P4228

   
Sensing Method Pyroelectric effect in TGS crystal material. Temperature changes from the scene cause charge to build up / decay on the inner face of the target material.
Sensor Type / Size EEV Pevicon P8092, 18mm circular target area
Lens Parameters 18mm f/0/7 giving 50 field of view. Fixed focus by moving tube/yoke assembly at build
Dynamic Range / Control 60C, automatic iris in lens
Display 38mm CRT with magnifier
Sensitivity (MDTD) <500mK, usually ~300mK in 'Pan' with a skilled operator
Power Source Internal carrier with 10 'AA' cells. Used LR6 alkaline, or optionally NiCd
Power System Battery regulated to 8.7V, camera ~4W (
Video Output BNC, produced in 60Hz / 525 line and 50Hz / 625 line variants
Image Processing Direct image or 'chopped'. Later builds of P4228 added a 1-field digital image store to give a constant image in chop mode
Manufacturer Status Built as 'EEV'. Obsolete, no longer serviced.
Number and Years Built Low 100's from 1981 - 1985
Export Status Not controlled
Publicity P4221 camera datasheet
Pevicon tube P8092 datasheet

Related Cameras

The P4200 was the first camera product from EEV, mainly as a vehicle to demonstrate Pevicon tubes. It was a contemporary product of the P4221 with a narrow field of view lens, manually focussed, for laboratory. It included access to a full set of tube adjustments and controls.
P4200 datasheet

The first trial with the fire service was 'hands-free', due to the camera weight. The camera appears to be a variation on the P4200

The P4222 was a contemporary product of the P4228 with a narrow field of view lens, manually focussed, for portable use. It included a crude temperature measuring/comparing function based on driving the video to black. An attempt was aslo made to use a 2/3" tube but resolution was not sufficient due to thermal conduction across the target material
P4222 datasheet

Hobby user information

Rechargeable batteries may be used in the 'AA' carrier, but the battery indicator is not accurate
These cameras are now very rare finds. The P4228 was supplied with a full service manual.


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Heritage TICs EEV P4221 & P4228 page 9 April 2019  All tradename © respective owners