The concept of a general purpose intrinsicallysafe system to multiplex several hazardous areaswitches over a single cable pair to the safearea was pioneered by Safety Technology in1982.The original S10 switch contact multiplexerretains its popularity, and has recently beenenhanced and introduced into the RTK range ofhazardous area products. The benefits to berealised in savings of cable pairs and zenerbarriers were soon apparent to a number ofmajor organisations, both in the construction ofnew plant and in the resulting effective increasein existing cable capacity to facilitate plantextensions.Neither of the systems described in thefollowing pages require any separate powersupplies to the hazardous area equipment, allpower requirements and data signals may becarried on a single cable pair.The encapsulated hazardous area units occupya particularly small volume, and are easilyhoused in compact panels or junction boxesappropriate to the installation. >

The S10/SA receiver unit gives relay changeover contacts and LED drive outputs foreach of the ten input circuits connected to the hazardous area transmitter. The system includes effective fault monitoring in which the normally energised monitor outputs are de-energised on data corruption. Introduced as the worlds first intrinsically safe switch multiplexer, the popularity of the simple and compact S10 system remains undiminished. The S10/HA transmitter accepts signals from switch contacts, and transmits their status to the safe area receiver on a single cable pair, which also carries the power...