dust detection

[clarke]

i need to detect when dust is present in an exhaust stack and was wondering if anyone knows of any probes or sensors that could be used. I have heard of using triboelectric sensors but these are exspensive and seem to be abit ott for what i want. I have tried using a differnetial pressure switch to monitor any change in pressure between clean and dirty side of the filter when we get a ripped filter bag but there wasnt any significant change in pressure so therefore it didnt work, but i am willing to listen to any suggestions.

 

[IRstuff]

What level of dust are you trying to detect? Most smoke detectors use devices that essentially detect dust

http://www.protectowire.com/products/aspirated_smoke_detection.htm

Also:

http://www.environmental-expert.com...ucttype=2&idcategory=788&idmainpage=0&level=0

Also, dust reduces optical transmission, so measuring changes in optical transmission might work as well.

TTFN

FAQ731-376

 

[BJC]

Gooogle up "opacity meters", They come in sizes for smoke stacks to exhaust pipes for diesel trucks. Most use a light source that shines through the dust/smoke.

 

[itsmoked]

A common problem. A great solution is specular reflection, just like fog horns work, and they need to be accurate.

A light is flashed and if more than X amount of back-scatter is detected by a sensor next to the lamp, then there is fog = run horn.

You can use this same method in a stack. You set up the light, and a receiver next to it, and then run a permanent purge air into the barrel of the instrument to prevent any contamination of the sensors.

Someone must make this.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[IRstuff]

see:

http://www.rand.org/pubs/monograph_reports/MR974/MR974.AppA.html

TTFN

FAQ731-376

 

[Comcokid]

There are systems that detect when a standard HVAC filter is dirty and needs changing. These use pressure sensors that measure full-scale pressure difference of only a few inches of mercury. Your exhaust stack system is not quite the same, but when you tried differential pressure, did you try a sensor with a very small full scale range?

 

[clarke]

Thanks comokid the filter typically runs at 13millibars obviously this changes between clean and dirty but for the purpose of what i was doing i used a 0 to 15mbar guage and then set the switch to sense if the pressure dropped below 13mbar. There was no cange of pressure shown on this gauge when the bag was split(cut a hole in the bag with a knife) and the switch didnt pick it up either, the switch was a dwyer series 1910 with a dwyer magnehelic gauge. Dont know if you have any ideas why it didnt work but would appreciate any input.