Sensor Electronics SEC Millenium Series Instruction And Operation Manual page 383

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;
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;
SEC 3120 16-bit Modbus Manual
For Version 1.2 and above
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.
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.
o All sensor regions in accordance with the number of reported
maximum attached sensors (see unit register 42922) are
independently readable and writeable (42101 - 42899).
o 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.
o 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.
o Unit region nine (42901 - 42999) will function normally as
described in this document, unaffected by sensor role.
Page 44 Of 46
December 2012
Sensor Electronics Corporation
P/N 1580282, Rev. 1, 20121228