How Thermocontrol in The Egg Incubator and Hatcher Works

At least we can find two models of thermocontrol or thermostat in the egg incubator and hatcher. First model is wafer type and the second is more sophisticated one, digital thermostat.

Wafer Thermostat

Wafer thermostat expands its height following surrounding increasing temperature and pushes the mechanical microswitch to turn off electrical current passing it. The heater or incandescent bulbs wired to the switch then turned off and stop their emitting heat. As temperature decreases following the lost of emitted heat, thermostat height decreased and releases its pressure to microswitch to let it back to do the job passing current to heater or bulbs. The process then repeated and regulated temperature maintained.

Wafer thermostat is the simplest form of thermocontrol device. Despite of its simplicity and cheap price, this model is actually has a lot of drawbacks. The wafer thermostat body itself store the heat received and need time to release. The wait state of releasing this self contained heat causing the device is less sensitive to surrounding temperature changes and significant temperature fluctuations may occur. Accceptable value of fluctuation to hatch eggs sucessfully claimed with this device manufacturer is 1.5 degree Celsius. Bad news, in fact it’s often up to 3 degree Celsius.

Wafer thermostat and microswitch are mechanical devices. Thermostat stroke may change frequently and time after time operator should adjust to acceptable value. Mechanical contact also prone to fire spark and get burned. Badly adjusted thermostat stroke would shorten microswitch life.

The last drawback, wafer thermostat contains chemical fluid inside. Frequently up and down stroke may cause its body cracked and leak the fluid out contaminating surrounding and the device then fail to do the job.

Digital Thermocontrol

If we think to create or assemble it ourselves, it’s true to say that this type of device is sophisticated and complicated one. But as an user, it is not more complicated than wafer thermostat, even simpler to install. There are 3 groups of wire to install. First input cord for mains current, second output cord for heater and the last one is sensor cable and the attached sensor. That’s all.

Digital thermostat has temperature sensitive probe/sensor. Its sensitivity may vary from 0.1 up to 0.5 depends on its type. The sensor may sense temperature and changes its resistance or output voltage that can be interpreted as linear temperature change.

The varied voltage changes represent varied temperature changes. It then compared to given value determined by user by adjusting potentiometer or digital up and down button. Said that predetermided value is 380mV that represent 38 degree Celsius, the comparator IC then send a signal to microcontroller to stop current delivery to heater when it sense voltage near or equals to 380mV from the sensor. Just it. We don’t have to think a lot about it. The result is incredibly stable as it loop speed may up to 20MHz or 20 million times a second. The speed that impossible acquired by mechanical type thermostat.

Digital thermocontrol tend to use SSR or solid state relay so burned contact problem completely avoided.

One of its disadvantage is it price. But we pay for what we get, don’t we?