STORY 2: "Heat value is like a water"

To make it easier to understand, we will classify soldering irons into two types: "Temperature saturation type" and "Temperature control type".

This seems to difficult to understand. What is the difference between these two types?

First, I'll talk about the "Temperature saturation type". The maximum amount of current flows through this type of soldering iron; In other words, it is always "ON".

I see! Then, the iron temperature must increase without limit. I don't want such hazardous soldering iron.

Ha-ha-ha (Laughing). Now, look at this graph.

When the temperature saturation type soldering iron is energized, the iron temperature will increase to a certain temperature and then will not increase any more. This temperature is called the "saturation temperature", which is the specified operating temperature of the soldering iron.

You mean the iron temperature will not increase without limit. Why?