[Code of Federal Regulations]

[Title 40, Volume 31]

[Revised as of July 1, 2006]

From the U.S. Government Printing Office via GPO Access

[CITE: 40CFR1065.305]



[Page 712-713]

 

                   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 713]]



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.