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Optical smoke chambers

sjb741

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Am working on a (non-safety crtical, 2nd line of defence) industrial smoke sensor project. We are using an RE46C200 chip and we are at last seeing nice results. However these rely upon a smoke chamber taken from an existing domestic detector.

Basically these chambers have to
  • Permit the passage of smoke
  • Very thoroughly exclude ambient light
  • 'Swallow' reflections
  • Arrange things so that the IR detector cannot 'see' the emitter. That means the detector can only receive illumination by means of IR light scattered by the smoke
We sourced very 'similar looking' chamber on Alibaba (;)). It is far harder to use though and results are disappointing - the detector seems to see the emitter regardless of smoke.

Both detectors are 3cm diameter and have very similar external-light baffles.

In the 'good' chamber, the emitter is a 5mm LED and is offset away from the circumference of the chamber . It also has firm clips to hold the LED and both emitter and detector have only small apertures (for IR light) in the plastic moulding. The central chamber baffle is fixed.

The 'bad' chamber has several small differences
  • Seems designed for a 3mm IR LED emitter (5mm does not fit)
  • Lack of emitter clip
  • Emitter protudes into the diameter of the chamber
  • Rotatable central baffle (no sure which way is correct). This includes a way to screw into the chamber without disrupting the light path.
  • No light-path restriction at detector side, just 'wide open'
  • A couple of myterious slots (to the outside) and clips at the detector side. I am wondering if there should be a small insert here.
Does anyone out there either know where we can source a chamber like the first, or any other ideas?
 

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