Page 9 - untitled

Brinsea – The Incubation Specialists Incubation Handbook Brinsea – The Incubation Specialists Incubation Handbook

4.2. Measuring Humidity and Weight Loss Hygrometers are electronic or mechanical devices that measure humidity by a physical change of a substance. Hair
hygrometers have a dial indicator connected to a fine filament of a material that changes length according to the
The humidity in an incubator may be measured using two methods: Wet Bulb Thermometer or Hygrometer. In both humidity and moves the dial indicator across a graduated scale. Electronic hygrometers measure the change in
cases air flow is required so these devices do not give accurate results in still air machines. electrical resistance of a small chip of moisture sensitive material and tend to be more accurate than mechanical
hygrometers. The Brinsea Humidity Management Module uses this type of sensor to display the humidity and to
The Wet Bulb Thermometer uses two thermometers, one of which has a moist cotton wick covering its bulb. The control a pump system to add water to maintain the desired humidity.
other end of the wick is placed in a water reservoir. Water evaporates from the wick and this cools the thermometer
bulb slightly. The lower the humidity of the air around the wet bulb the greater the rate of evaporation and the greater Warning: cheap, inaccurate hygrometers can be worse than having no hygrometer. The ideal humidity level for the
the cooling effect. egg, which can be effected by variation in shell thickness and porosity, is always best monitored by checking the egg
weight loss.
Relative humidity (always expressed as a percentage) is related to the difference between the dry and wet bulb
thermometer readings. Do not confuse wet bulb temperatures (which are sometimes quoted in books) with Weight Loss Calculations
percentage relative humidity. The following table gives the wet bulb temperatures which relate to percentage relative
humidity. (The figures assume a dry bulb incubation temperature of 37.5ºC / 99.5ºF.)

If the weight of an egg was not measured when it was laid it may be estimated using the formula:

RH level (%) WB Temp °F WB Temp ºC Fresh Laid Weight (g) = Length (cm) x Breadth (cm) x Breadth (cm) x 0.548

20 69.1 20.6 Using the fresh laid weight and the weight loss percentage recommended for the species the daily weight loss may
25 71.6 22 be calculated:
30 74.1 23.4
35 76.5 24.7 Daily Weight Loss = Fresh Laid Weight x Desired % Loss to pip
40 78.8 26 Number of Days to Pip
45 80.8 27.1
50 82.9 28.3 Some breeders prefer to use change of Egg Density as the measure of water loss from the egg:
55 84.9 29.4
60 86.7 30.4 Egg Volume = Length (cm) x Breadth (cm) x Breadth (cm) x 0.51
65 88.5 31.4
70 90.1 32.3 Egg Density (g/cm3) = Egg Weight (g)
75 91.9 33.3 Egg Volume (cm3)
80 93.6 34.2
85 95 35 Estimated Daily Change in Egg Density:
90 96.6 35.9
95 98.1 36.7 Daily Change = Egg Density at Time (T1) – Egg Density at Time (T2)
100 99.5 37.5 Time (T2) - Time (T1)

If the incubation temperature is different, compensate by adjusting the wet bulb temperature accordingly. For
example: if using the incubator at 36ºC with a wet bulb temperature of 26ºC, calculate the RH level using the 27ºC
wet bulb temperature: = 46%. Note that the wet bulb thermometer will read the same as the ordinary
(dry bulb) thermometer either at 100% RH or, more probably, when the wick dries out.

16 17