Analog Output/3 Alarms; Overview - Emerson NGA2000 Instruction Manual

Model NGA2000 I/O Modules

2-1 OVERVIEW

See Section 1 for information that applies to
all I/O Modules.
The Analog Output with 3 Alarms I/O Module
uses up to three of the SPDT relay outputs.
These outputs are configured as common,
normally open and normally closed.
Each of these alarms trips a relay to alert the
user that some variable is outside of the de-
sired range. Alarms can be set to trigger on
high/low, high/high, low/low or just single high
or low setpoints.
Alarm deadband is also a software program-
mable item with an upper limit of 20% of
fullscale.
There are four alarm categories: Gas Concen-
tration, Warning or Failure, Status and Valid-
ity.
Gas Concentration
Gas concentration can be expressed as a
percentage of the current range or as an ab-
solute value. Alarms can be set to alert the
user of low concentration, high concentration
and percent of range values.
Warning or Failure
Warning indicates one or more software con-
figured limits on any network variable (other
than gas concentration) has been exceeded.
Examples of these secondary variables are
flow rate and internal voltage. A software re-
Rosemount Analytical Inc. A Division of Emerson Process Management
SECTION 2

ANALOG OUTPUT/3 ALARMS

Instruction Manual
set or other resolved software failure would
also be reported.
Failure indicates an unrecoverable hardware
or software failure (i.e., some component is
not responding to network communications or
a safety related failure such as lack of purge
air in a Flame Ionization Detection Analyzer
Module has been noted).
In the event of a Warning or Failure alarm,
gas concentration values displayed on the
Operator Interface or present on output lines
are accurate.
Status
Status can describe either Maintenance or
Calibration Mode.
Maintenance - a user enters the menu sys-
tem; this can be sued to alert the system of
unauthorized entry.
Calibration Mode - alerts the user that the
Analyzer Module is being calibrated.
Gas concentration values are accurate.
Validity
Validity describes a condition in which gas
concentration values present on the Operator
Interface or output lines should be considered
invalid. The Analyzer Module alerts the sys-
tem that an error in gas concentration is pre-
sent.
See Figure 2-1 for a flowchart depicting menu
screens related to this I/O Module.
Analog Output/3 Alarms
748275-F
September 2003
2-1