Page 106 - Gas Detection Systems Training Manual

Communication Parameters
Protocol: Modbus RTU slave.
Baud rates: 1200, 2400, 4800, 9600, 19200 bps field selectable, Word length 8.
Parity: Odd, Even, None, field selectable.
Stop Bits: 1 or 2, field selectable.
Electrical Interface:
o RS 485, multi-drop 2-wire positive/negative (using A/B nomenclature). o Transmit and Receive: Half Duplex.
o Useable speed will depend on cable length.
Modbus addressable: 1-247 (up to 254 if ONLY SEC 3120 units on a single bus).
Modbus Sensor Read Only Registers
Gas concentration (expressed as an integer scaled up by factor) representing the units of measurement for that specific sensor s current gas type (PPM, % LEL, %V/V, etc.)
Operating Status (normal, calibrating, self test, start up, in an alarm (low, mid high) or fault
Gas category Type (toxic, hydrocarbons, oxygen, etc.)
Sensor firmware version
Sensor serial number
Alarm relay mode (trip above or below threshold, audible or normal action)
Modbus address (Network ID)
Sensor Range and Gas Factor
Sensor Status and Error code, as well as Cell Test Warn code
ASCII Gas name and Gas Units Name
Modbus Sensor Read/Write Registers
Alarm thresholds (low, mid and high set points)
Zone ID (Network Zone ID)
Execute Self Test
Modbus 3120 Unit Read Only Registers
Unit Operation Status
Unit Fault Relay Reason Code
Unit Serial Number
Maximum Number of Sensors That Can Be Attached
Unit Clock- Read Current Time
Unit Type
Unit Firmware Version Info
SEC 3120 16-bit Modbus Manual Page 5 Of 46 Sensor Electronics Corporation For Version 1.2 and above December 2012 P/N 1580282, Rev. 1, 20121228