a intervalos

adv. on and off, at intervals

= at intervals
Ex: Usually a new bulletin will be issued at intervals, for example, monthly, weekly or daily = Normalmente, un nuevo boletín se publicará a intervalos, por ejemplo, mensualmente, semanalmente o diariamente.

= at + Adjetivo + intervals
Ex: A free-standing terminal is a computer in its own right, which processes and stores data about the transactions and which may also exchange data with a central computer at predetermined intervals, say at the end of a working day.