What's the spectral sensitivity of a pyroelectric vidicon tube? - Page 1
Forum section: electronics / general

author: Ben321
author_rank: Frequent Contributor
timestamp: December 30, 2020, 05:01:19 am
content: Some older cameras (including thermal cameras) used vidicon tubes. Most of these were sensitive to visible light, but a pyroelectric version was created that was sensitive to LWIR instead. Does anybody know what the spectral sensitivity curve of this type f thermal imager is? It's so old of a technology, that I can't even find datasheets for it by using Google search.

author: Fraser
author_rank: Super Contributor
timestamp: December 30, 2020, 11:13:10 am
content: Datasheets for the EEV Pevicon tubes are to be found at the URL below thanks to forum member Bill_Whttp://fire-tics.co.uk/4428.htmhttp://fire-tics.co.uk/datasheets/P8092_datasheet.pdfhttp://fire-tics.co.uk/datasheets/P8226_datasheet.pdfFraser

author: Fraser
author_rank: Super Contributor
timestamp: December 30, 2020, 12:49:22 pm
content: The Pevicon tube is to be found in several early portable fire fighting thermal cameras.Examples are the EEV P4428, ARGUS 1 and the original ISG Talisman MK1 fire fighting cameras. These use technology that will be familiar to those older techs who have worked on Vidicon based CCTV and broadcast cameras. A significant difference is the requirement for a chopper wheel in front of the Vidicon Tube faceplate if the need for movement in the thermal scene is incompatible with the application. A Pevicon only produces an output on scene content change so a camera that does not incorporate a chopper wheel must be panned or the observed target must be in motion. The P4428, Argus 1 and Talisman MK1 all incorporate a chopper wheel but in the P4428 it can be disabled if desired.Do not be fooled by the relatively old technology of the Vidicon camera tube. Whilst it cannot truly compete with modern imaging arrays in terms of image quality, it is never the less a very useful imaging sensor. Look at the various versions of the P8226 Pevicon tube details in its datasheet .... that tube has an impressive band coverage capability that is set by the target material. When modern broadband imaging arrays had yet to be invented, these Pevicon and advanced Vidicon tubes were nothing short of miraculous in terms of offering affordable broad band imaging to the scientific community. If well cared for they have a decent life span as wellThey may be thermionic vacuum tube technology but to me that is just another form of sensor rather than something to be discounted purely due to its age.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: December 30, 2020, 01:05:45 pm
content: Some of us are discovering the capabilities of affordable SWIR Vidicon based cameras from companies like Electrophysics and Hamamatsu .......https://www.eevblog.com/forum/thermal-imaging/swir-electrophysics-micronviewer-7290a-user-manual/From speaking to Electrophysics, it is clear that the 7290A NIR/SWIR camera was very popular within the scientific community but sadly had to be discontinued when Hamamatsu ceased production of the specialist Vidicon tube that is at the heart of these cameras. Had the tubes and deflection coil assemblies remained in production, the cameras would have continued to be manufactured. Electrophysics/Sofradir are still supporting the 7290A cameras that remain in use as users wish to continue using these relatively simple and affordable imaging systems. The alternatives are very expensive modern semiconductor FPA cameras. A popular use of the 7290A was laser beam imaging fir beam quality and alignment purposes. For such a task, the 7290A is an excellent choice. It can be operated without a lens and the laser beam applied to the Vidicon tubes target faceplate vis a suitable ND filter. This provides excellent beam quality monitoring without concern over the effect of a lens structure between the beam and the target.The popularity of these ‘old’ cameras is aptly demonstrated by the high prices that good examples fetch on the secondary market. £1000 is not unusual. Even heavily used examples can achieve surprisingly high prices if they still work. Abused units will often have exterior damage and burn marks on the Vidicon tube target from exposure to powerful laser beams without adequate ND filter protection. Even burnt target units that can still present an accurate image without too much lag are still useable for laser beam alignment.Fraser

author: Ben321
author_rank: Frequent Contributor
timestamp: December 31, 2020, 03:03:05 am
content: Quote from: Fraser on December 30, 2020, 12:49:22 pmThat's strange. Why does it require motion? I always thought a pe-vidicon tube was the same as a normal vidicon, except for the photosensitive material being sensitive to LWIR instead of visible light.

author: Ben321
author_rank: Frequent Contributor
timestamp: December 31, 2020, 03:10:46 am
content: Quote from: Fraser on December 30, 2020, 01:05:45 pmWhy did Hamamatsu discontinue making the tubes? Is there a chance that some other company will take up where they left off, and make them again (although under a different brand name, to avoid violating Hamamatsu's trademark)? Maybe a company that caters to making components for technology suitable for the hobbyist market? Almost any R&D company or university that needs one probably already has one, with a few remaining to the hobbyist market on eBay. If these were to be made and sold again by some new company, then the intended market would probably be the hobbyist market. I just hope that ends up happening.

author: _Wim_
author_rank: Super Contributor
timestamp: December 31, 2020, 06:35:22 am
content: Quote from: Ben321 on December 31, 2020, 03:10:46 amI do not think any other company will make them. Price would be way above hobbyist market level anyway to build a complete camera with it.I suspect that the solid state solution will continue to drop in price, so R&D companies & universities should not be long without an affordable SWIR solution. To drop down to hobbyist level or have Ebay flooded with 2nd hand SWIR camera's will take quite a while however I am afraid.Cheapest solution for NIR and a small part of the SWIR band is to use an industrial CMOS camera and install an IR long pass filter. By turning up the gain and exposure time lasers up to about 1200-1300µm can be visualized.

author: _Wim_
author_rank: Super Contributor
timestamp: December 31, 2020, 06:44:04 am
content: Quote from: Ben321 on December 31, 2020, 03:03:05 amIt is not because of the vidicon, but because of the pyroelectric photosensitive material.From wikipedia:Pyroelectricity (from the two Greek words pyr meaning fire, and electricity) is a property of certain crystals which are naturally electrically polarized and as a result contain large electric fields. Pyroelectricity can be described as the ability of certain materials to generate atemporaryvoltage when they are heated or cooled. The change in temperature modifies the positions of the atoms slightly within the crystal structure, such that the polarization of the material changes. This polarization change gives rise to a voltage across the crystal.If the temperature stays constant at its new value, the pyroelectric voltage gradually disappears due to leakage current.The leakage can be due to electrons moving through the crystal, ions moving through the air, or current leaking through a voltmeter attached across the crystal.So only a change in temperature generates a voltage. By having a chopper wheel a continuous change is created, allowing the camera to also take images of a steady state environment.

author: Fraser
author_rank: Super Contributor
timestamp: January 01, 2021, 01:15:46 pm
content: On the subject of Pyroelectric effect based imaging systems, it is worth mentioning the IRISYS produced their own Pyroelectric thermal imaging FPA’s for use in their People Counting and low resolution camera systems. The first FPA was only 16x16 pixels but the Redeye sensor array dis increase in size to 47x47 pixels over time. IRISYS still manufacture advanced people counting and tracking systems fir the retail market but stopped production of thermal imaging cameras when FLUKE (or its mother company) bought them.I own examples of the IRISYS people counting units and the thermal imaging cameras. I spoke with a tech from IRISYS regarding conversion of a thermal people counter to a thermal imaging camera. He explained that this was what they did to create the early 16x16 pixel cameras that they produced. The Pyroelectric FPA had a very useful feature when used as a people counter...... if an object in the field of view did not move, it faded away and was effectively hidden from the image processing stages. This meant that inanimate ‘clutter’ in the scene was effectively ignored through physics rather than requiring image processing or clever AI technology ! The Pyroelectric effect was useful fir a static thermal people counting and tracking sensor but made use of the technology fir a thermal camera less ideal. The answer was the same as that fir a Pevicon tube based camera..... change had to be introduced to the scene by artificial means. In the case of the early IRISYS low resolution thermal cameras it was a 50:50 ratio chopper that was rotated in front of the Pyroelectric FPA. The chopper ‘wheel’ introduced the change in the scene that the FPA needed in order to create a signal output fir targets in the scene that were not moving with respect to the FPA. The chopper ‘wheel’ was a very simple design driven by an inexpensive motor that is more commonly found in a CD player deck. The chopper ‘wheel’ was not as complex in design as that found in the Pevicon orcBST technology based cameras but it provided what was required fir the simple low resolution IRISYS cameras.For those who do not think they have seen an IRISYS Pyroelectric Redeye FPA based camera, think again. The FLUKE VT02 and VT04 ‘visual thermometers’ are actually IRISYS designed and built Redeye Pyroelectric FPA thermal imaging cameras. The Redeye 6A FPA used in them is a 32x32 pixel sensor and interpolation is commonly used to increase the apparent resolution at the display.I did a teardown of the VT02 prototype here.....https://www.eevblog.com/forum/thermal-imaging/fluke-vt02-thermal-camera-visual-thermometer-teardown/A teardown of the early generation IRISYS Pyroelectric camera is to be found here....https://www.eevblog.com/forum/thermal-imaging/thermal-camera-teardown-the-irisys-iri1011-by-fraser/Background on IRISYS and their cameras.......https://www.eevblog.com/forum/thermal-imaging/irisys-thermal-camera-history-models-iri4035-camera-unboxing-by-fraser/Fraser

author: Fraser
author_rank: Super Contributor
timestamp: January 01, 2021, 02:07:43 pm
content: Research into Pyroelectric thermal imaging sensor arrays continuesThere is even work on dual band Pyroelectric FPA’sSome interesting links.......https://www.spiedigitallibrary.org/conference-proceedings-of-spie/4077/0000/Theory-of-realizing-dual-band-thermal-imaging-with-pyroelectric-FPA/10.1117/12.385571.short?SSO=1https://www.ama-science.org/proceedings/download/ZGLmAj==https://uspto.report/patent/app/20190033139https://www.hamamatsu.com/resources/pdf/ssd/infrared_kird9001e.pdfFraser