This is a continuation of the previous two circuits. This circuit controls the temperature in a miniature oven that holds a stable dual voltage reference.
Temperature Measurement and Control
In colder seasons or locations this will maintain the temperature at a higher level. A mini fan in the equipment ensures external heat does not reach the oven, fan keeps the larger chassis cool.
This circuit may fail if the equipment is in very hot open locations, big heaters, hot machines or direct sunlight falls on equipment OR the Lab is not cooled to near normal ambient temperatures.