Introduction
Although the "long wave" preheating system with calrod elements for predrying the PCBs to evaporate the solvent from the flux is one of the best systems, it has its drawbacks when a mix of boards with different heat demands have to be soldered. Also the demand for the preheating of fluxes which need higher temperatures, or the thermal requirements for certain SMDs may ask for a system that will respond faster than the calrod elements. On the other hand one must prevent thermal amadge to (conventional) components due to a too high temperature.
The attached sheet will give information about what to expect from different types of preheating systems.