BA307E, BA327E, BA308E & BA328E intrinsically safe ... - Ex-Baltic

64.2 Remote indicationThe indicators may be driven via an intrinsicallysafe interface from a 4/20mA safe area signal toprovide a remote display within a hazardous area.The type of intrinsically safe interface is not critical,either a Zener barrier or a galvanic isolator may beused, providing that Ui, Li and Pi of the indicatorare not exceeded and the voltage capability of the4/20mA signal is sufficient to drive the indicatorplus the interface.When a high integrity earth connection is alreadyavailable, a Zener barrier is usually the leastexpensive option. If an earth connection is notavailable or isolation is required, a galvanic isolatoris the correct choice.If one side of the 4/20mA current loop may beearthed, a single channel Zener barrier providesthe lowest cost protection. If the 4/20mA signal isnot isolated, then two Zener barriers, a twochannel Zener barrier or a galvanic isolator mustbe used.Fig 3 shows the alternative circuits which may beused.Fig 3 Alternative circuits for remote indicationin a hazardous area