I recall the use of light globe filaments used to detect air flow. Current is passed thru the filament and the resistance is measured. >From memory the results are repeatable and the can be calibrated to give reasonable measurements. Justin On 28 August 2016 at 12:52, James Cameron wrote: > Thanks for the replies on liquid level sensing. > > Another aspect of the problem is detecting fan failure, which can be > done by measuring current or a rotation sensor, but doesn't actually > tell if the fan is moving air. Blocked intake makes fan spin faster; > it is not moving as much mass, but the same could happen if the > chimney is working well from the heat of the day. > > I'm interested in comments on anemometers, air flow sensors, mass flow > sensors, or pressure sensors relative to ambient. > > The space to work within is a few yards of 3" diameter plastic pipe. > > I'm fine with drilling it, because if I change my mind I can plug it > with kapton tape or silicone caulk. > > The environment can be excessively dirty or wet. Occasionally an > insect gets into the system, lays eggs, and a few days later a swarm > will try to leave. Occasionally the dew point is just right for > condensation in the pipe. > > The fan (at the moment) is a 90mm 12V DC rated at 59 CFM, 3.8 watts, > 0.32 amps. The corners get cut off and foam padding added to fit it > into 100mm nominal (4") plumbing pipe. Wish for circular fans. ;-) > > -- > James Cameron > http://quozl.netrek.org/ > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .