Instruction manual

Instruction Manual
760006-A
September 2001
Rosemount Analytical Inc. A Division of Emerson Process Management Description and Specifications 1-1
Model NGA 2000 Platform
SECTION 1
DESCRIPTION AND SPECIFICATIONS
1-1 THE NGA 2000 CONCEPT - INTRODUCTION
NGA 2000 stands for "Next Generation Ana-
lyzer". It describes a new concept in gas Ana-
lyzer design. The basis for this concept is the
division of the traditional Analyzer functions into
modular parts, connected by a digital communi-
cation link called LON.
Traditional Analyzers contain the "physics" - the
mechanism for detecting the gas in question -
and a means of controlling the operation of and
getting data from the physics. This normally
consists of a display with associated controls on
the front of the box, and "I/O" (input/output)
consisting of an analog or sometimes RS232
output, together with some relay contacts, on
the back. Power is supplied by an AC connec-
tion to the wall plug. Each Analyzer in a system
has to contain all of these components.
In the NGA 2000 concept, the physics is sepa-
rated from everything else into an "Analyzer
module", and a single "Control module" or
"Platform" (so called) contains the control, dis-
play, I/O and power supply components.
Communication between the Analyzer module
and the Control module is by means of a so-
phisticated digital communication system made
by the Echelon Corporation, called LON-
WORKS™ or LON™. There are many subtle-
ties involved in such systems, but the NGA
2000 and the LON hide almost all of these from
the user. A great deal of the sophistication of
the NGA 2000 concept is involved in making the
communication system extremely simple to use
and in removing the complexity that, for exam-
ple, your MIS administrator has to deal with
while managing the LAN (Local Area Network)
you probably have to use at work!
A typical NGA 2000 system then consists of a
number of different types of Analyzer modules
connected to a single Platform, with some se-
lection of I/O provided according to the particu-
lar needs of the user. Control of the entire
system takes place through the single Platform,
and any I/O to the system goes through it. (It is
also possible for a computer to talk directly to
the Analyzer modules without the need of a
Platform, but that is outside the scope of this
document.)
1-2 THE DIGITAL COMMUNICATIONS SYSTEM –
INTRODUCTION
The NGA 2000 uses a proprietary digital com-
munication system made by Echelon Corpora-
tion, called LONWORKS™ or LON™ for short.
It is a sophisticated system that deals with most
of the subtleties required without user interven-
tion or knowledge, but there are certain aspects
of it of which you should be aware.
The LON sends data in packets called "Vari-
ables". These are named, so that, for example,
the main output of an Analyzer is contained in a
variable called "PVA". Its range is contained in
a variable called "CRANGE". These variables
are emitted by the source and read by other
modules on the network that are interested in
them.
I/O Modules contain input variables of the same
name, and when the I/O is "bound" to an Ana-
lyzer module, the contents of the Analyzer's
PVA are automatically communicated to the
I/O's PVA, so that it now knows what the Ana-
lyzer's reading is. It can convert it to a 4-20mA
signal, or whatever it is configured to do. Obvi-
ously it is important that the I/O Module knows
which Analyzer to listen to!
The way we tell the I/O Module which Analyzer
it should pay attention to is to "bind" it to that
Analyzer. This process selects an Analyzer,
selects an I/O Module, and ties them together
so that the set of Analyzer variables is bound to
the equivalent set of I/O variables, and the two
act as if they are one unit. The process itself is
described below, and it is much easier in V2.3
than in V2.2 and earlier versions. It is the only
thing you have to do to configure the LON.