There are many kinds of SCR modules, many applications, and many advantages. Even the heating method is not one. Choose a heating method you like to use.

1. Phase shift triggered heating SCR conduction Angle is adjusted, the voltage changes, so as to adjust the heating power;

2. Zero-crossing trigger heating is commonly referred to as solid-state relay. When heating, the voltage does not change, but it is actually a pulse on-off signal.

Generally speaking, phase shift trigger is selected, but phase shift trigger has interference with the frequency of the power grid, high power performance is more prominent, but the general industrial occasion does not matter, because according to practical experience, to no longer use the heater on the same side of the oscilloscope class of the power grid frequency requirements of high-precision instruments will not have anything.

Moreover, phase shifting heating is a dynamic voltage reduction, so it is good for extending the life of the heating element. Zero-crossing trigger is simple and stable, which can usually save a trigger board. The trigger signal of SCR is generally 0-5V or 1-5V pulse. 

The high-speed output control of the S7-200 is not recommended. The general practice is to choose the temperature control module, the first thermocouple or thermal resistance temperature signal into PLC, PID