Typical heaters are made very simple with a resistance that generates heat but can be complex to control. For example, see the design picture for a temperature controlled fan. There has to be a sensing element which needs to send an input to the control processor or element which in turns needs to regulate the power to be sent to the heater. This adds complexity to the design of the software to the control as well it adds complexity to the circuit board and all the peripherals. And then there is cost.
A simpler design of a heater uses an effect that can simplify the design. In this case, the material offers all the control element and the heating element all in one. These materials are electrically conductive plastic that is conductive at a specific temperature and resistive at a higher temperature. Call the temperature that it changes its property – “set temperature”.
Below the “set temperature” the plastic is conductive and allows the current to flow, this causes the material to heat.
As the material heats, it starts becoming insulated and then stops conducting and this lowers the current flow through the plastic. As the material cools, it again allows the current to flow and thus heats it up again.
This makes for a simple heater.
There are two issues with this simple logic – First, the plastic needs to be made specifically for one temperature. Second, the temperature control is not precise. It is estimated that it can be +/- 7C. However, this makes for such a simple design that it is used in several applications.
he one that is used at home is a water pipe heater that prevents the water from freezing in the water pipes on a cold day. Below, or close to the freezing temperature, the heater does allow the current to flow and above the freezing temperature it does NOT allow the current to flow. This makes for such a good simple wire that is self-regulated.
It will be good to think about other complex processes that can be reduced to simplicity if one can tolerate the flexibility or inaccuracy.