U.S. Code of Federal Regulations
Regulations most recently checked for updates: Mar 30, 2023
(a) This section describes how to determine the accuracy, repeatability, and noise of an instrument. Table 1 of § 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
(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 § 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 § 1065.750.
(4) Use the instrument to quantify a NIST-traceable reference quantity, y
(5) Sample and record values for 30 seconds (you may select a longer sampling period if the recording update frequency is less than 0.5 Hz), record the arithmetic mean, y
(6) Also, if the reference quantity is not absolutely constant, which might be the case with a reference flow, sample and record values of y
(7) Subtract the reference value, y
(8) Repeat the steps specified in paragraphs (d)(2) through (7) of this section until you have ten arithmetic means (y
(9) Use the following values to quantify your measurements:
(i) Accuracy. Instrument accuracy is the absolute difference between the reference quantity, y
(ii) Repeatability. Repeatability is two times the standard deviation of the ten errors (that is, repeatability = 2 ·
(iii) Noise. Noise is two times the root-mean-square of the ten standard deviations (that is, noise = 2 · rms
(10) You may use a measurement instrument that does not meet the accuracy, repeatability, or noise specifications in Table 1 of § 1065.205, as long as you meet the following criteria:
(i) Your measurement systems meet all the other required calibration, verification, and validation specifications that apply as specified in the regulations.
(ii) The measurement deficiency does not adversely affect your ability to demonstrate compliance with the applicable standards in this chapter.