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Registered Member #799
Joined: Wed May 23 2007, 05:24PM
Location: Barrie. Ontario, Canada
Posts: 25
Hi all,
I am trying to build an electronic dew sensor for some device that can not tolerate water condensation. I have found one simple design that uses a resistive dew sensor element , an Op-amp as a comparator and an Opto coupler. Yo can find this design under the website:
However the resistive element is hard to find and I have found a store which carries the capacitive sensor.
My question is how would the circuit change if I use a capacitive element.I have already done a search on the net and did not find anything for the capacitive version.
Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
If you wanted to use the capacative sensor, you need to excite it with an AC waveform and put a capacitor in series with it to act as a potential divider. You can then rectify / integrate this signal and compare it with a reference.
I didn't know that VCRs had dew sensors in them - every day is a school day!
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Condensation sensors (white/green/grey wafer in VHS VCRs) are not humidity sensors.
btw capacitive sensors are typically more sensitive, but have limited range (<95% non-condensing RH).
What is the intended application? Honeywell at one point made HVAC and instrumentation sensors. I forget who is licensed to sell their product line these days.
Registered Member #799
Joined: Wed May 23 2007, 05:24PM
Location: Barrie. Ontario, Canada
Posts: 25
The application needs a condensation sensor, not a humidity sensor. I have to find a broken VCR to take apart!! Some Thermoeleric cooler for a spectrometer is producing water condensations. The idea is to shut it off when this happens and produce some kind of warning signal.
I think Sulaiman's and data stream's ideas probably were to route to go.
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
Some people use a safe gas layer to prevent water condensation (Canned Air (non-cfc), Helium, or welding Argon). Perhaps something similar to the setup for CCD optics in telescopes may prove useful (encase all but the sensor window in epoxy.)
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
If you need a true humistor there is one in an atmospheric radiosonde you can get them on eBay very cheaply. There's also a thermistor, a capacitive anemometer and a water-activated battery.
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Dew sensor
