Experience with a humidity sensor?

Question

I'm working on an Arduino project logging humidity, temperature and air pressure in a sewer for 30 days at a time. The environment is very hostile, 99 - 100% humidity and full of sulphuric acid. (The acid comes from hydrogen sulphide combining with the humidity). The prototype works fine and I'm about to make the final version of the hardware for deployment into the sewer.

I'm using a HYT 221 humidity sensor and while it is supposed to be chemical resistant I have the funny feeling it is not going to last the desired month in the sewer. I suspect that the housing I'm going to use (Jiffy box) will allow moisture in, even with an o-ring around the sensor. I also need to have the air pressure sensor exposed and that has no filter or protection.

Has anyone else had any experience exposing sensors to hostile environments and not having them die?

mcb1 · Answer

I also need to have the air pressure sensor exposed and that has no filter or protection.

You could house the air pressure sensor inside a sealed pressurised container with a 'bladder'. Any changes in the air density will exert force onto the bladder and raise the pressure inside which the sensor can measure. It should be relatively easy to calibrate, and keeps it from the toxic environment. For the electronics, I suggest housing them inside a rubber or latex balloon (used for RC What Kind of Balloons Do You Use to Protect RC Electronics? ) or similar then inside a sealed container, with only the connections external. If possible apply positive pressure into the sealed container, avoid using double insulated wire at the external junction, as the air will leak down the outer sheath. I'm afraid your humidity sensor needs to be exposed, so pick something designed for chemical environments, or throw it away after 30 days. Let us know what you designed and how it copes. Mark

Former Member · Answer

Hi, 'Conformal Coating' (best and costly, but the cost is going down somewhat) or try e ncapsulating (soft potting ) insides of jiffy box or specific components, depending on your budget. Keep in mind the addition of capacitance/impedance, so recalibration maybe necessary after post potting/coating of board (check the material's permittivity, E). Pretest and mask whatever you do not want to be protected (i.e. adjustable pot screws, mounting holes, etc) with conformal coating or potting before sending it out. If you are doing it yourself, very messy and wear a good breathing mask.