Page 345 - 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