Relative Humidity

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					            Measuring Relative Humidity
Relative Humidity is a measure of the amount of moisture in the air. It is normally expressed as a
percentage, however in fixed temperature instances such as incubators, it is sometimes simply
expressed as the ‘Wet Bulb Reading’ or the ‘Wet Bulb Depression’ .

Humidity is important in the incubation of eggs. Too little humidity, and the egg loses moisture
causing failure at hatching, or if severe, premature death of the embryo. Too much humidity and
the chicks can develop deformities and hatch with unhealed navels.


Relative Humidity can be simply measured in the classroom.


You need:

      Two Thermometers
      Bowl of water
      Length of shoelace (hollow type)
      Rubber Band
      Relative Humidity Chart


Method

      Thread the shoelace over the bulb of one thermometer and fix with the rubber band.

      Place the other end of the shoelace in the water bowl and notice the water travel up the
      shoelace to the bulb.

      The temperature of this ‘wet bulb’ thermometer will lower.

      When the temperature has stabilized, take your reading.

      Subtract this reading from the dry bulb
      temperature to obtain the Temperature
      Difference

      Use the Relative Humidity Chart to calculate
      the actual Relative Humidity.

      Take readings on different days and during
      different weather conditions and notice the                  Therm1
      differences in humidity.
                                                         Relative Humidity Chart
To Calculate Relative Humidity

Read the Dry Bulb Temperature along the vertical rows. Read the difference between Dry & Wet
Bulb temperatures along the top Column. The intersection of these two figures indicates the
Relative Humidity expressed as a Percentage.
                                                           Difference between Dry & Wet Bulbs – Degrees Celsius

                                                           1   2   3   4   5   6   7   8   9 10 11 12 13 14 15 16
                                                        10 88 77 65 54 44 34 24 14 5
                                                        11 88 77 66 56 46 36 26 17 8
                                                        12 89 78 68 57 48 38 29 20 11 3
                                                        13 89 79 69 59 49 40 31 23 14 6
                                                        14 90 79 70 60 51 42 33 25 17 9         2
         Air Temperature – Degrees Celsius (Dry Bulb)




                                                        15 90 80 71 61 52 44 36 27 20 12 5
                                                        16 90 81 71 62 54 46 37 30 22 15 8          1
                                                        17 90 81 72 64 55 47 39 32 24 17 10 4
                                                        18 91 82 73 65 56 49 41 34 27 20 13 7
                                                        19 91 82 74 65 58 50 43 35 29 22 15 9           3
                                                        20 91 83 74 66 59 51 44 37 30 24 18 12 6
                                                        21 91 83 75 67 60 52 46 39 32 26 20 14 8            3
                                                        22 96 83 76 68 61 54 47 40 36 30 22 16 11 5
                                                        23 96 84 76 69 62 55 48 42 36 30 24 18 13 8             3
                                                        24 96 84 77 69 62 56 49 43 37 31 26 21 15 10 5
                                                        25 96 84 77 70 63 57 50 44 38 33 27 22 17 12 7              3
                                                        26 96 85 78 71 64 58 51 46 40 34 29 24 19 14 9              5
                                                        27 96 85 78 71 65 59 52 47 41 36 30 25 21 16 11 7
                                                        28 96 85 79 72 65 59 53 48 42 37 32 27 22 18 13 9
                                                        29 96 86 79 72 66 60 54 49 43 38 33 28 24 19 15 11
                                                        30 96 86 79 73 67 61 55 50 44 39 34 30 25 21 17 13
                                                        31 96 86 80 73 67 62 56 51 45 41 36 31 27 22 18 14
                                                        32 97 86 80 74 68 62 57 52 46 42 37 32 28 24 20 16
                                                        33 97 86 80 74 69 63 58 52 47 43 38 34 29 25 21 17
                                                        34 97 86 81 75 69 64 58 53 48 44 39 35 30 26 23 19
                                                        35 97 87 81 75 70 64 59 54 49 44 40 36 32 28 24 20
                                                        36 97 87 81 76 70 65 60 55 50 45 41 37 33 29 25 21
                                                        37 97 87 82 76 70 65 60 55 51 46 42 38 34 30 26 23
                                                        38 97 88 82 76 71 66 61 56 51 47 43 39 35 31 27 24
                                                        39 97 88 82 77 71 66 61 57 52 48 44 40 36 32 28 25
                                                        40 97 88 82 77 72 67 62 57 53 48 44 40 37 33 29 26

				
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Description: Relative Humidity