Originally Posted by mattd2
What is the benifit of the SCR over a SSR?
they are not exactly comparable like that. SSRs can be made out of SCRs, or also MOSFETs or some other types of solid state switches.
most zero crossing SSRs are made out of a pair(s) of SCRs (silicon controlled rectifiers, a type of thyristor). they are zero crossing because of the fact that SCRs dont stop conducting until the current falls below a threshold level, like when the AC waveform crosses zero. SCRs are used in pairs because they only conduct current in one direction, so two are needed to conduct AC.
non-zero crossing SSRs normally have MOSFETs doing the switching, as their state is not dependant on the amount of current flowing thru it, and can turn on or off at any given time.