Thermostat Demonstration
The simplest thermostat control scheme is a threshold temperature with a “hysteresis” window so that the switching isn’t too frequent.
A thermocouple is in an enclosure with a heater. The thermostat measures the enclosure with the thermocouple and then sends a signal to a switch that turns a heater on and off. That switch is connected to the energy source that will warm the enclosure.
![Schematic](./figures_static/lab/thermostat-schematic.png)
If the thermostat turned on and off at the same temperature, the system would switch very frequently. Instead, there is a window around the desired temperature and the system behaves as below for the switching behavior.
![Hysteresis Graph](./figures_static/lab/thermostat-hysteresis.png)
Thermocouple
The voltage across a thermocouple varies as the temperature varies. A common thermocouple, type K, varies 41 microvolts for each degree Centigrade. Using a sensitive amplifier we can increase this small voltage up to a few volts that can be read by a microcomputer.