[Code of Federal Regulations]
[Title 40, Volume 18]
[Revised as of July 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR92.127]

[Page 459-460]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 92--CONTROL OF AIR POLLUTION FROM LOCOMOTIVES AND LOCOMOTIVE ENGINES--
Table of Contents
 
                       Subpart B--Test Procedures
 
Sec. 92.127  Emission measurement accuracy.

    (a) Good engineering practice dictates that exhaust emission sample 
analyzer readings below 15 percent of full scale chart deflection should 
generally not be used.
    (b) Some high resolution read-out systems such as computers, data 
loggers, etc., can provide sufficient accuracy and resolution below 15 
percent of full scale. Such systems may be used provided that additional 
calibrations are made to ensure the accuracy of the calibration curves. 
The following procedure for calibration below 15 percent of full scale 
may be used:
    (1) If a 16-point gas divider is used, 50 percent of the calibration 
points shall be below 10 percent of full scale. The gas divider shall 
conform to the accuracy requirements specified in Sec. 92.112.

[[Page 460]]

    (2) If a 7- or 9-point gas divider is used, the gas divider shall 
conform to the accuracy requirements specified in Sec. 92.112, and shall 
be used according to the following procedure:
    (i) Span the full analyzer range using a top range calibration gas 
meeting the calibration gas accuracy requirements of Sec. 92.112.
    (ii) Generate a calibration curve according to, and meeting the 
applicable requirements of Secs. 92.118 through 92.122.
    (iii) Select a calibration gas (a span gas may be used for 
calibrating the CO2 analyzer) with a concentration between 
the two lowest non-zero gas divider increments. This gas must be 
``named'' to an accuracy of 1.0 percent (2.0 
percent for CO2 span gas) of NIST gas standards, or other 
standards approved by the Administrator.
    (iv) Using the calibration curve fitted to the points generated in 
paragraphs (b)(2)(i) and (ii) of this section, check the concentration 
of the gas selected in paragraph (b)(2)(iii) of this section. The 
concentration derived from the curve shall be within 2.3 
percent (2.8 percent for CO2 span gas) of the 
gas' original named concentration.
    (v) Provided the requirements of paragraph (b)(2)(iv) of this 
section are met, use the gas divider with the gas selected in paragraph 
(b)(2)(iii) of this section and determine the remainder of the 
calibration points. Fit a calibration curve per Secs. 92.118 through 
92.122 for the entire analyzer range.