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When the module is operated in conjunction with a Sentry controller, the alarm relay setup (See section 5.3) should be set to “Sentry”, allowing the Sentry controller to manage alarm relay action rather than the 5100-XX-IT Gas Sensor Module. 1.4.2 MODBUS OPERATION An RS-485 Modbus RTU serial interface allows direct connection to standard PLCs and DCSs. The Module Address Switch (section 4.5) allows the user to select up to 15 different Modbus addresses. Also, an additional 254 Modbus addresses a