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S
TARTUP AND
O
PERATION
748332-D Rosemount Analytical June 1997
3-9
NGA 2000 Non-Dispersive Infrared Analyzer
minimum of 11 data points. (A more accurate curve can be obtained as the user
approaches 21 data points. If urgent, a curve can be created with as few as four
points, but this is only a temporary fix. A more accurate curve should be created as
soon as possible.)
These data points can be obtained with an accurate gas divider or other flow mixing
device. Before calculating coefficients, the data must be normalized to ranges of 0 to
1 units for both percent and concentration readings. Then, the axis must be reversed
as illustrated in Figures 3-7 and 3-8. A multiple linear regression is then used to
calculate coefficients. (For example: If the range is 0 to 5000 ppm and readings are 0
to 100%, then divide all of the concentrations by 5000 and the readings by 100. Put
the normalized concentrations on the Y-axis and the normalized readings on the X-
axis.)
These data points can be entered into any program capable of computing a fourth-
order polynomial curve. This curve will be the mirror image of the curve on the
Calibration and Data Sheet provided in the rear of this manual; however, the
linearization coefficients will be different. Use the coefficients calculated with the
curve in the polynomial shown on the previous page.
After taking the data points, the operator may determine coefficients for user-specific
gas by either using any program capable of calculating a fourth-order curve fit or
calling the factory to have the specific coefficients calculated.
When entering the operator-determined coefficients, note that the microprocessor only
recognizes five significant digits to the right of the decimal point (e.g., 0.12345).
3.7 ROUTINE OPERATION
Set the NDIR Analyzer Module for desired operating range. Zero and span the
module, and then supply sample gas to the SAMPLE INLET at the rear of the module.
The NDIR Analyzer Module will now automatically and continuously analyze the
sample stream.
As a check of instrument performance, the operator should keep a log of zero/span
status.
Maximum permissible interval between calibrations depends on the analytical
accuracy required. A frequency of once every 24 hours is recommended initially, and
that practice should be continued unless experience indicates that some other interval
is more appropriate.
Readout accuracy is directly proportional to change in barometric pressure (i.e., a
change in cell pressure of 7.6mm of mercury will result in a readout error of about 1%
of reading). Therefore, if barometric pressure changes significantly, a recheck of
calibration against a span gas is advised. Also, an optional Pressure Compensation
Board is available that electronically compensates.
Содержание NGA 2000
Страница 1: ...NGA 2000 NON DISPERSIVE INFRARED ANALYZER MODULE Rosemount Analytical ...
Страница 6: ...CONTENTS iv June 1997 Rosemount Analytical 748332 D NGA Non Dispersive Infrared Analyzer NOTES ...
Страница 16: ...PREFACE P 10 June 1997 Rosemount Analytical 748332 D NGA Non Dispersive Infrared Analyzer NOTES ...
Страница 22: ...INTRODUCTION 1 6 June 1997 Rosemount Analytical 748332 D NGA Non Dispersive Infraraed Analyzer NOTES ...
Страница 54: ...REPLACEMENT PARTS 5 2 June 1997 Rosemount Analytical 748332 D NGA 2000 Non Dispersive Infrared Analyzer NOTES ...
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