Electronic module for controlling the energy in a Vapour Phase Soldering machine

As known, there are three parameters for controlling the thermal profile in vapour phase soldering machine; the paper refers to one of them - the electric energy from the AC mains introduced in the system in order to bring the thermal agent to the boiling point and to obtain the appropriate vapours density. The idea was to control the power dissipated in the heating element, one power resistor, by controlling the state of a switch instead of switching more power resistors. For 100% power dissipation the switch will be always ON, while for a lower power the switch will be closed from time to time by a microcontroller. During switching AC mains noise is produced that is dependant of the AC sinus at the actual switching point. To bring noise at its lowest value the switching should occur at 0 volt amplitude. This happens when sinus is ¿zero crossing¿ which is accomplished by using a zero-cross power opto-triac. The feedback is closed by a current transformer and an analog-to-digital convertor, constituted by the built-in feature of the microcontroller. The whole algorithm of control resides in a master microcontroller supervising all three parameters, which communicates with the electronic modules on SPI bus.