anyone recommend a good capacitive proximity sensor

[TF and the wire]

I'm looking at fitting a sensor in ducting that carried airborne paper dust to signal when there is a blockage. I'll locate it just before the usual place where it blocks up. I would like to avoid an optical device, as it would require regular cleaning, I'm thinking of a capacitive type that would give an output when the paper dust covers the sensing tip.

The last time I used thesewould bei the 80's an I seem to remember that they didn't work very well. Have they improved?

 

[JD6400]

Depends on what you are after , are you after make on blockage or break on blockage also 2 wire or 5 wire and the option of hold off or on timer , and what voltage range ?
We use most of the above on grain handling gear from several different suppliers , I can look out where we get it from if you can give a few more details

 

[Jamzie]

To be fair there are more fundamental issues with the product medium to be resolved before worrying about the switch voltage or contacts. The switch is specified against the product and granular size. Endress & Hauser have a good web site which will take you through the process although I would always recommend speaking to an engineer before buying. Not cheap, bough one in December that cost over £1k although they can be much cheaper depending on specification. Mobrey is another 'good' make.

 

[Bobster]

With it being paper dust, does the inside of the blow line fall under any Ex restrictions?

 

[ElectroChem]

Might be an idea to look at agricultural suppliers, we use 5 wire prox sensors for pellet feeders, being designed for farms they're robust and can come with adjustable sensitivity and delay settings. The ones we use are 240V powered and then a relay contact so no NPN/PNP hassles, I imagine ELV versions exist.

 

[SheffSimon]

Depending on the duct size, Endress and Hauser Soliphant FTE30 paddle type switches are very reliable we have found. They give a NO/NC volt free contact, and are suitable for ATEX zone 20 installation.

 

[thepurple1]

you could fit an air pressure sensor to give either 0-10volt or 4-20mA signal

 

[TF and the wire]

Thanks for the recommendations so far. Voltage range doesn't really matter, I'll adapt it to suit. I would avoid a two wire as these usually present indicator problems. I've seen the paddle type before where a rotating paddle stops when the area around it becomes blocked. I would prefer a simple small sensor that I can fix to the ducting easily and will give a change of signal when it is surrounded by paper dust.

 

[Knobhead]

Read #4. what you would prefer my not come in to the final decision.