[Code of Federal Regulations]
[Title 40, Volume 31]
[Revised as of July 1, 2007]
From the U.S. Government Printing Office via GPO Access
[CITE: 40CFR1065.305]

[Page 713-714]
 
                   TITLE 40--PROTECTION OF ENVIRONMENT
 
         CHAPTER I--ENVIRONMENTAL PROTECTION AGENCY (CONTINUED)
 
PART 1065_ENGINE-TESTING PROCEDURES--Table of Contents
 
                Subpart D_Calibrations and Verifications
 
Sec.  1065.305  Verifications for accuracy, repeatability, and noise.

    (a) This section describes how to determine the accuracy, 
repeatability, and noise of an instrument. Table 1 of Sec.  1065.205 
specifies recommended values for individual instruments.
    (b) We do not require you to verify instrument accuracy, 
repeatability, or noise.
    However, it may be useful to consider these verifications to define 
a specification for a new instrument, to verify the performance of a new 
instrument upon delivery, or to troubleshoot an existing instrument.
    (c) In this section we use the letter ``y'' to denote a generic 
measured quantity, the superscript over-bar to denote an arithmetic mean 
(such as y), and the subscript ``ref'' to denote the reference quantity 
being measured.
    (d) Conduct these verifications as follows:
    (1) Prepare an instrument so it operates at its specified 
temperatures, pressures, and flows. Perform any instrument linearization 
or calibration procedures prescribed by the instrument manufacturer.
    (2) Zero the instrument as you would before an emission test by 
introducing a zero signal. Depending on the instrument, this may be a 
zero-concentration gas, a reference signal, a set of reference 
thermodynamic conditions, or some combination of these. For gas 
analyzers, use a zero gas that meets the specifications of Sec.  
1065.750.
    (3) Span the instrument as you would before an emission test by 
introducing a span signal. Depending on the instrument, this may be a 
span-concentration gas, a reference signal, a set of reference 
thermodynamic conditions, or some combination of these. For gas 
analyzers, use a span gas that meets the specifications of Sec.  
1065.750.
    (4) Use the instrument to quantify a NIST-traceable reference 
quantity, yref. For gas analyzers the reference gas must meet the 
specifications of Sec.  1065.750. Select a reference quantity near the 
mean value expected during testing. For all gas analyzers, use a 
quantity near the flow-weighted mean concentration expected at the 
standard or expected during testing, whichever is greater. For a noise 
verfication, use the same zero gas from paragraph (e) of this section as 
the reference quantity. In all cases, allow time for the instrument to 
stabilize while it measures the reference quantity. Stabilization time

[[Page 714]]

may include time to purge an instrument and time to account for its 
response.
    (5) Sample and record values for 30 seconds, record the arithmetic 
mean, yi, and record the standard deviation, [sigma]i, of the 
recorded values. Refer to Sec.  1065.602 for an example of calculating 
arithmetic mean and standard deviation.
    (6) Also, if the reference quantity is not absolutely constant, 
which might be the case with a reference flow, sample and record values 
of yrefi for 30 seconds and record the arithmetic mean of the 
values, yref. Refer to Sec.  1065.602 for an example of calculating 
arithmetic mean.
    (7) Subtract the reference value, yref (or yref), from the 
arithmetic mean, yi. Record this value as the error, [egr]i.
    (8) Repeat the steps specified in paragraphs (d)(2) through (6) of 
this section until you have ten arithmetic means (y1, 
y2, yi,. . . y10), ten standard deviations, 
([sigma]1, [sigma]2, [sigma]i,. . 
.[sigma]10), and ten errors ([egr]1, 
[egr]2, [egr]i,. . .[egr]10).
    (9) Use the following values to quantify your measurements:
    (i) Accuracy. Instrument accuracy is the absolute difference between 
the reference quantity, yref (or yref), and the arithmetic mean of the 
ten yi, y values. Refer to the example of an accuracy calculation in 
Sec.  1065.602. We recommend that instrument accuracy be within the 
specifications in Table 1 of Sec.  1065.205.
    (ii) Repeatability. Repeatability is two times the standard 
deviation of the ten errors (that is, repeatability = 2 [middot] 
[sigma][egr]). Refer to the example of a standard-deviation calculation 
in Sec.  1065.602. We recommend that instrument repeatability be within 
the specifications in Table 1 of Sec.  1065.205.
    (iii) Noise. Noise is two times the root-mean-square of the ten 
standard deviations (that is, noise = 2 [middot] rms[sigma]) when the 
reference signal is a zero-quantity signal. Refer to the example of a 
root-mean-square calculation in Sec.  1065.602. We recommend that 
instrument noise be within the specifications in Table 1 of Sec.  
1065.205. Use this value in the noise correction specified in Sec.  
1065.657.
    (10) You may use a measurement instrument that does not meet the 
accuracy, repeatability, or noise specifications in Table 1 of Sec.  
1065.205, as long as you meet the following criteria:
    (i) Your measurement systems meet all the other required 
calibration, verification, and validation specifications in subparts D, 
F, and J of this part, as applicable.
    (ii) The measurement deficiency does not adversely affect your 
ability to demonstrate compliance with the applicable standards.