§ 1066.135 Linearity verification.
This section describes requirements for linearity verification that are unique to testing under this part. (Note: See the definition of “linearity” in 40 CFR 1065.1001, where we explain that linearity means the degree to which measured values agree with respective reference values and that the term “linearity” is not used to refer to the shape of a measurement instrument's unprocessed response curve.) Perform other required or recommended calibrations and verifications as described in 40 CFR 1065.307, with the exceptions noted in this section.
(a) For gas analyzer linearity, use one of the following options:
(1) Use instrument manufacturer recommendations and good engineering judgment to select at least ten reference values, yrefi, that cover the range of values that you expect during testing (to prevent extrapolation beyond the verified range during emission testing). We recommend selecting zero as one of your reference values. For each range calibrated, if the deviation from a least-squares best-fit straight line is 2% or less of the value at each data point, concentration values may be calculated by use of a straight-line curve fit for that range. If the deviation exceeds 2% at any point, use the best-fit nonlinear equation that represents the data to within 2% of each test point to determine concentration. If you use a gas divider to blend calibration gases, you may verify that the calibration curve produced names a calibration gas within 2% of its certified concentration. Perform this verification between 10 and 60% of the full-scale analyzer range.