Temperature Sensors for Linux

This comes from DigiTemp user Robert Graham, instructions on how to measure humidity using the wet bulb method.

I know there is a humidity sensor out there but for those of you who like to build things you can make a wet/dry bulb hygrometer similar in operation to a sling Psychrometers used to calibrate humidity sensors.

Using two DS18S20 one old fan from your junk pile and some white plastic PVC pipe. I made mine out of 5 PVC couplings and a 5-6 reducer seal at one end for the water reservoir.

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For the wick for the wet bulb, I used a new cottonshoelace. You do not have to have the fan but you will get very fast response if you do.

I have a chart showing the relation ship between the temperature of the drybulb and the temperature of the wet bulb.

......Relative Humidity Table.......
Dry Bulb
Temperature ........Wet Bulb reads °C lower than Dry Bulb
°C      1  2  3  4  5  6  7  8  9  10 12 14 16 18 20
 2 >>>> 84 68 52 37 22 8
 4 >>>> 85 70 56 42 29 26 3
 6 >>>> 86 73 60 47 34 22 11
 8 >>>> 87 75 63 51 39 28 18 7
10 >>>> 88 76 65 54 44 33 23 14 4
12 >>>> 89 78 67 57 47 38 29 20 11 3
14 >>>> 89 79 69 60 51 42 33 25 17 9
16 >>>> 90 80 71 62 54 45 37 29 22 14
18 >>>> 91 81 73 64 56 48 41 33 26 19 6
20 >>>> 91 82 74 66 58 51 44 37 30 24 11
22 >>>> 91 83 75 68 60 53 46 40 34 27 16 5
24 >>>> 92 84 76 69 62 55 49 43 37 31 20 9
26 >>>> 92 85 77 70 64 57 51 45 39 34 23 14 4
28 >>>> 92 85 78 72 65 59 53 47 42 37 26 17 8
30 >>>> 93 86 79 73 67 61 55 49 44 39 29 20 12 4
32 >>>> 93 86 80 74 68 62 56 51 46 41 32 23 15 8  1
34 >>>> 93 87 81 75 69 63 58 53 48 43 34 26 18 11 5
36 >>>> 93 87 81 75 70 64 59 54 50 45 36 28 21 14 8
38 >>>> 94 88 82 76 71 65 60 56 51 47 38 31 23 17 11
40 >>>> 94 88 82 77 72 66 62 57 52 48 40 33 26 19 13
42 >>>> 94 88 83 77 72 67 63 58 54 50 42 34 28 21 16
44 >>>> 94 89 82 78 73 68 64 59 55 51 43 36 29 23 18

For example @20° C if there is a 1 degree difference that would = 91% relative humidity @20° C if there is a 10 deg difference that would = 24% relative humidity.

This design was based on one I have seen at some green houses, it is rugged and can get fertilizer on it and keeps working. When both sensor read the same you need to add water.