sentences:  The Pentex system, which evolved beyond TXE2, was exported to over 30 countries and was largely responsible for Plessey winning the Queen's Award for Exports in 1978.Because of their common control design, isolation (inability of the exchange to set up calls) of the entire exchange was always a possibility and very occasionally happened.This potential weakness had been at least partially recognised in the design of the exchange type, so the most critical common control units were split into three sections and each section was duplicated into an A-side and a B-side.