simple and accurate determination of overall shop relative humidity

[Bob Blarney]

Over time, many mechanical or electronic hygrometers become inaccurate, or there may be areas in your shop where the humidity is higher or lower than the overall environmental humidity.  Here's a way to get an accurate overall value.

 

1.  Obtain an accurate thermometer, a shopvac, a jar of water, and a small piece of cloth.

2.  Leave a jar of water to stand in the shop so that it equilibrates with the ambient temperature.

3.  Measure and note the temperature of the air

4.  Wet the cloth in the jar, and then place it over the thermometer's sensing area (bulb or probe).

5.  Place the covered thermometer at  the mouth of the shop vac intake hose, turn on the shop vac and note the lowest observed temperature.

6.  Determine the difference between the dry and wet temperatures.

7.  Consult published humidity tables such as:   https://www.pharmaguideline.com/2013/09/principle-of-hygrometer-and-its-use-in-manufacturing.html

Edited June 6, 2018 by Bob Blarney

[jud]

Or find a wet and dry thermometer, wet the wet bulb and giver her a spin, do every 4 hours and log it. That is what was done in the Navy in the early 60's but those instruments they disappeared from the bridge and quarterdeck. You have came up with a good substitute for those Wet and Dry Thermometers we used years ago, same principal, so the results should be good. See there are some avable today that aren't very expensive, those like we used I did not see during my quick search but they were expensive instruments and would still be expensive to make today.

jud   

. 

[Bob Blarney]

4 hours ago, jud said:

Or find a wet and dry thermometer, wet the wet bulb and giver her a spin, do every 4 hours and log it. That is what was done in the Navy in the early 60's but those instruments they disappeared from the bridge and quarterdeck. You have came up with a good substitute for those Wet and Dry Thermometers we used years ago, same principal, so the results should be good. See there are some avable today that aren't very expensive, those like we used I did not see during my quick search but they were expensive instruments and would still be expensive to make today.

jud   

. 

A good quality psychrometer is indeed difficult to find these days.   For this purpose, I use a lab-grade digital thermometer, but a traditional alcohol (or mercury) thermometer works well too.