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There are hundreds of models of thermostats on the market today both digital and analogical, some without decimal point. 

 

 

 

 

And some with decimal point, but the majority of them don't have sufficient accuracy for the purpose of incubation of egg, and hence I will stick out my neck and say that thermostats are now obsolete for the incubator and i don't use them other than for controlling the temperature of my brooding cages and maybe as a cheep backup in case the main controler fails in the incubator

 


What you need is a Process controller that has PID, What is PID ? you might ask

Proportional, Integral, Derivative

 The best way to explain it is as follows

Controlling the heating of a tank.  For simple control, you have two temperature limit sensors (one low and one high)  switch the heater on, the low temperature limit sensor turns on the heater and then turn the heater off when the temperature rises to the high temperature limit sensor.  This is similar to most home air conditioning & heating thermostats. and the temperature is up and down like a yoyo within  1º or 2ºthis means minimum 0.5º above and below what we require, Not good enough. 

In contrast, the PID controller would receive as input the actual temperature and control a valve that regulates the flow of gas to the heater.  The PID controller automatically finds the correct (constant) flow of gas to the heater that keeps the temperature steady at the set point.  Instead of the temperature bouncing back and forth between two points, the temperature is held steady.  If the set point is lowered, then the PID controller automatically reduces the amount of gas flowing to the heater.  If the set point is raised, then the PID controller automatically increases the amount of gas flowing to the heater.  Likewise the PID controller would automatically compensate for hot, sunny days (when it is hotter outside the heater) and for cold, cloudy days. Ahh that sounds better and it works too

Another brief example:-

 Driving along in your car at a steady 30kph when you come to a hill you have to press the accelarator pedal in order to maintain the speed, once over the hill the car starts to speed up and we have to lift off the accelarator in order return to the speed required, we are functioning as a PID controler.

 Applying this to an incubator means a rock steady temperature control that i have yet to see on a normal thermostat, all you need to do is look at the top of the range incubators in nearly all manufacturers and they use them and the best bit is there is very little difference in the price