Hello. I would like to sense the presense of a clear non-flammable liquid in a 5/16" x 30" tubular reservoir. I have no choice but to insert the sensor from the top of the tube in my application (not by the side). Does anyone know a small enough sensor or sensor design that will fit inside this tube (5/16" inner dimension)?
Thanks. Marcel
-- Use a self-heated thermistor. When not in contact with the liquid the heat capacity of its environment will be lower than when it's in contact with the liquid, giving you a sharply delineated region between contact and non-contact (presence and absence) of the fluid.
If you can use conductivity, make a sensor from mineral-insulated cable with a hermetic termination and electrodes at the wet end.
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
Depending on how clear the liquid is, you can use a fiber-optic detector. Normally the light goes down one fiber and is total internal reflected into the other. The liquids index is greater than air's so when the liquid hits the air side of the reflecting surface, the total internal reflection stops because the index change is too small for the angle.
-- -- kensmith@rahul.net forging knowledge
On a sunny day (26 May 2004 06:23:17 -0700) it happened snipped-for-privacy@aol.com (Marcel Gonzalez) wrote in :
2 electrodes. Or if the thing is metal, only one. Fluid need to be a bit conductive. Electrode via 1 M to + 5. Voltage will drop if in fluid. JP
Is that always true for all combinations of liquid and gas (plus vapor from the liquid, of course).
-- If you doubt it, why don't _you_ do the legwork needed to prove that it isn't true and then post your incontrovertible evidence?
Pretty much, unless you'r near the triple-point of the liquid in question.
There are reflective sensors with integrated photodiode / LED inside. I thingk the way they work is that when immersed in liquid the light "escapes" the housing, when out of the liquid total internal reflection occurs and thelight is sensed by the internal detector. From memory the sensing bit was about the same size as a 5mm LED - the ones I saw had a ferrule assembly for bulkhead/thread mounting. Try RS or Farnell if they sound useful. I think the specs mentioned refractive index of the fluid - I know they work for petrol.
rob
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