Reference Manual
748384-C
September 2003
Rosemount Analytical Inc. A Division of Emerson Process Management
Introduction 1-7
NGA2000 Reference
1-3 ANALYZER MEASUREMENT RANGES
NGA analyzer modules have four ranges avail-
able. These ranges normally do not correspond
to any physical settings in the analyzer, they are
there for operator convenience. It is possible to
separately zero, span and linearize each range,
in which case you may well not get the same
reading on a given gas, if you change the op-
erational range. Some analyzers do change an
internal setting on a range change, though they
never do this dynamically based on the signal
within a range. If they do this, or if the filtering
time is set to a value greater than zero, there
will normally be a short term "glitch" as the ana-
lyzer reaches its new value.
The dynamic range of the analyzer on a single
range is normally quite great, and it is often only
necessary to change ranges if you are recording
the analog output of the I/O module. However
for traditional reasons some users like- to oper-
ate between 20% and 80% of a range, and thus
change ranges anyway, even though this makes
no actual difference to the analyzer's operation
or resolution.
It is possible to set the I/O module to produce
an output independently of the analyzer's cur-
rent range. You can make the I/O module stay
on a particular range, regardless of the ana-
lyzer, or you can make the analyzer stay on a
particular range and force the I/O to change its
ranges in response to a remote (digital line)
command. You can connect two or more I/O's
to a single analyzer, and make them respond to
different analyzer ranges, thus getting two si-
multaneous outputs, one for low range resolu-
tion, and the other for upset conditions.
If you make the I/O operate independently of the
analyzer, it will change its output range within
about 120 micro seconds of a remote command
(for an I/O with a 5 MHz clock, later I/O's with a
10 MHz clock respond within 80 micro sec-
onds). There is no "glitch" at all in this case,
since the analyzer is not affected by the range
change request.
If the I/O has to make the analyzer range
change, the total transaction may take up to half
a second, and there may be a glitch in this time.
In general the only reason for making a real
range change is to use a different linearizer
curve on a lower signal. It may also be useful to
get a better signal to noise ratio if the range
change is drastic, such as changing from 0 -
10,000 ppm. to 0 - 10 ppm on a FID. On the
former range the resolution is about 0.1 ppm,
whereas on the latter it is about 0.01 ppm.
a. Basic
Instructions
1. Enter
the
Main menu
2. Select
Basic controls...
3. Edit
the
Measurement range number:
line.
b. Advanced
instructions
To change range fullscale values
1. Enter
the
Main menu
.
2. Select
Expert controls and setup
3. Select Analyzer module setup.
4. Select
Gas measurement parameter
s..
5. Select
Range setting
s.. .
6. Edit the range upper and lower set-
points as desired.
7. Press the left arrow key.
8. Select
Linearization parameters
...
9. Edit any linearization parameters you
have to due to the range change, such
as which linearizer is used on which
range, or what the linearization coeffi-
cients are.
To alter the maximum or minimum pos-
sible ranges
1. Press "HOME" or enter the
Main menu
.
2. Select
Technical level configuration
...
3. Select
Service menus...
