The technique of intrinsic safety was originated in England for mine signalling, following a serious mine disaster in 1913. The first surface certificate was issued in 1936 and the first formal standard in 1945, but it was not until the 1960s that the technique came into its own for process measurement and control, with the development of the shunt-diode safety barrier based on the Zener diode.
This paper outlines the development of the technique and describes some typical applications of the shunt-diode barrier and its more recent companion, the isolating interface device. It also looks briefly at the new IS instruments being made possible by advances in low-power semiconductor technology.
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