Question
I'm looking for a recommendation on a humidity sensor for some long term grape storage rooms. After talking with a few people I'm told the humidity sensors for this duty will have to be something special. The combination of high humidity and low temperature environments is tough duty for a sensor, along with being able to withstand the sulfur dioxide atmosphere. (R.R.)
Answer
Good quality humidity sensors cost at least $500. Two companies with good equipment are Vaisala <http://www.vaisala.com/en/products/humidity/Pages/default.aspx> and Omega Engineering <http://www.omega.com/>, but there are others. Be sure to buy the calibration kit so you can periodically check the instrument. SO2 is a problem. I doubt any sensor will stand up to this, but you can ask the company reps about this. You will probably need to locate the sensor so you can remove it or seal it from the storage air during fumigation. You may also be able to set the sensor up so that a time clock controlled peristaltic pump brings storage air to the unit at programmed times. The pump and piping system will affect your RH reading so you would need to control/measure humidity on the basis of dew point temperature. –Jim Thompson