Dear Mr. Vishnia

Re: Wet/dry Humidity Meter

We received 2 Humidity Meters manufactured by Mr. David Vishnia of D.M.P. Engineering to be used in an egg incubator.

These humidity meters are ”wet” thermometers – thermometer with a cotton fiver around its tip, absorbed with water. The water vaporization around the tip of the thermometer causes the temperature to drop relative to the percentage of the humidity inside the incubator.

Usually, an identical “dry” thermometer is being used beside the “wet” thermometer, so the difference between the two temperatures could be measured. This temperatures’ difference is typical for any humidity rate in any temperature environment.
Standard International charts enable to evaluate this datum to the relative humidity.

 David Vishnia’s innovative idea’s are as follows:

1. In the incubators built by D.M.P. Engineering, the heat is evenly and constantly spread throughout the incubator, so one can give up the “dry” thermometer and use only one thermometer – the “wet” one.
In addition, Mr. Vishnia uses a very accurate Calibrate Thermometer  (± 0.1 ºC (with a low heat capacity, which achieves its thermal balance in few seconds.

 2. Above the red temperature scale is blue scale showing pre-calculated Standard International charts of relative humidity at various temperatures. This saves time and efforts for the user.

In the professional literature, such thermometers could be accurate ± 2% relative humidity, which is the same accuracy for digital thermometers based on electric capacity.
While checking at the incubating temperature range (35-39 ºC), I realized that the temperature reading at the calibrate scale in a “wet” thermometer only, could be changed in 1.5% ±. For example, if the humidity scale would calibrate for a temperature of 37 ºC,
This, approximately, would be the accurate reading around all incubating temperature at the above range. At the worst case, the deviation would be only 3.5% ±.
This is a very high accuracy and it gives optimized humidity adjustment in the incubator for ideal weight loss in the eggs and therefore optimum hatching.
However, I could not check to what extent does the inside incubator air blowing influence on the humidity meter.
One should care that the air blowing speed would not be less than 3 meters per a second on the thermometer, otherwise the temperature measured in the “wet” humidity meter would be higher than expected. As a result of this, a higher temperature than the real one would be measured.

Well done! Congratulations!