Science Buddies: "Ask an Expert"

Hi there

Am designing a simple chicken egg incubator for home use, I have a 3A Solid state relay. 4 70Watt lamps as my heat source, a K type thermocouple,and a PID temperature regulator, am find it a challenge connecting these to work properly.
Lately I have tiried hacking the PID so as to connect the SSR to it but the PID wont regulate the temperature as set to it.
can some one help me out there. circuit diagrams or schematics are also welcome.
I got the information from: //www.growyourownfood.com.au/poultry/chickensix.htm

Thermocouples are difficult use to sense temperatures in the range that an egg incubator needs to operate in.
Thermocouples operate on having a sensing junction and a reference junction. The small voltage created by the temperature difference between the sensing junction and the reference junction is INDEPENDENT of the temperature of the reference junction. This means you have to independently know the temperature of the reference junction. If your appliaction was sensing temperatures in the 1000-4000 degree F range, using a room/ambient air temperature junction that was 60-100 degrees (40 degree unknown) wouldn't introduce a significant error in the measurement. This means you need to know what the temperature of your reference junction is if you need an accurate absolute temperature measurement with thermocouples.

This is why the article you referenced used an RTD. Resistance temperature devices don't require an independent reference. Their resistance is a function of absolute temperature.