So even if you use one phase and the same phase this timing needs to be correct

No, you're mistaken here; if you look at the graph, you'll notice the first transmission is *at* the zero crossing. The 2nd after 2.778 ms, and the 3rd after 5.556 ms. The next *zero crossing* happens after 8.33 ms (or 10 ms in the case of 50 Hz), but this is irrelevant as no transmission happens at this time. Anyway, trust me, the TW523 does work happily on 50 HZ.

Regards,

Anand.