Page 145 - Gas Detection Systems Training Manual

Sensor Roles and Modbus
The SEC 3120 allows three major modes or roles of operation regarding attached sensors;
1. Single Sensor Role- In this role, the SEC 3120 works much more like the SEC 3100 and 3100MB16, monitoring and reporting on only one attached sensor to its sensor one connector while ignoring any other attached sensors. The effect is a single sensor, single network ID, and total exclusive control of the units relays, screen and LEDs.
Modbus Effects- since the 3120 (head) operates as if it only has a single sensor attached;
o The address ALL sensor region (42001 - 42099) will be ignored and generate exception messages if addressed by a master. No reads or writes will be allowed.
o Sensor region one will only be readable and writeable (42101 - 42199).
o Sensor regions two through eight (42201 - 42899) will be ignored and if accessed will generate exception messages to the master.
o Unit region nine (42901 - 42999) will function normally as described in this document, unaffected by sensor role.
2. Identical Sensor Role- In this role, ALL sensors attached (more than one) must have identical gas types, detection types and gas ranges. The purpose of this role is to provide redundancy and reliability to sensitive detection operations where relays should not be activated unless at least two sensors are in agreement as to the actual gas concentration levels independently measured. The relays are controlled in a logical "AND" operation for alarm levels, while faults continue to operate the fault relay in a logical "OR" configuration- meaning ANY sensor with a fault will cause the fault relay to energize.
Modbus Effects- since the 3120 (head) operates as if it has identical sensors attached;
o o o o o
The address ALL sensor region (42001 - 42099) will be allowed to apply thresholds/set points and calibration values to ALL sensors to streamline setup and configuration.
All sensor regions in accordance with the number of reported maximum attached sensors (see unit register 42922) are independently readable and writeable (42101 - 42899).
A change written in threshold/set point registers in any given sensor region will result in that value being copied to the other corresponding sensor parameter.
Writes to Zone ID (42x11) must be identical in all sensors regions, and in fact, the final region written (typically 42211) will set the final value for all sensors.
Unit region nine (42901 - 42999) will function normally as described in this document, unaffected by sensor role.
SEC 3120 16-bit Modbus
For Version 1.2 and above December 2012 P/N 1580282, Rev. 1, 20121228
Manual Page 44 Of 46 Sensor Electronics Corporation