§ 1066.140 Diluted Exhaust Flow Calibration - Linearity and Calibration Requirements

Sep 4, 2026

Section § 1066.140 explains how to calibrate flow meters for diluted exhaust constant-volume sampling (CVS) systems and related configurations. It sets scope and frequency for calibration, defines when calibrations are required after upstream or downstream changes, and provides options for ex-situ CFV/SSV calibration. The section also details linearity verification criteria for flow meters, temperature and pressure measurements, and requirements for analytical instruments not covered by referenced standards.

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§ 1066.140 Diluted Exhaust Flow Calibration

Overview

Scope and frequency

Ex-situ CFV and SSV calibration

Reference flow meter

Configuration

PDP calibration

Linearity criteria and verification for measurements

§ 1066 .140 40 CFR Ch. I (7–1–14 Edition) for an example of calculating an arithmetic mean. (3) Linearity criteria. The values measured during linearity verification for flow meters must meet the following criteria: | xmin(a1 ¥1)+a0 | ≤ 1% · Q˙max ; a1 = 0.98¥1 .02; SEE = ≤ 2% · Q˙max ; and r2 ≥ 0.990. (c) Perform linearity verifications for the following temperature measurements instead of those specified at 40 CFR 1065.307(e)(7): (1) Test cell ambient air. (2) Dilution air for PM sampling, including CVS, double-dilution, and partial-flow systems. (3) PM sample. (4) Chiller sample, for gaseous sampling systems that use thermal chillers to dry samples, and that use chiller temperature to calculate dewpoint atthe chiller outlet. For testing, if you choose to use the high alarm temperature setpoint for the chiller temperature as a constant value in determining the amount of water removed from the emission sample, you may verify the accuracy of the high alarm temperature setpoint using good engineering judgment without following the linearity verification for chiller temperature. We recommend that you input a simulated reference temperature signal below the alarm setpoint, increase this signal until the high alarm trips, and verify that the alarm setpoint value is no less than 2 °C below the reference value at the trip point. (5) CVS flow meter inlet temperature. (d) Perform linearity verifications for the following pressure measurements instead of those specified at 40 CFR 1065.307(e)(8): (1) Exhaust back pressure at the tailpipe exit. (2) Barometric pressure. (3) CVS flow meter inlet pressure. (4) Sample dryer, for gaseous sampling systems that use either osmoticmembrane dryers or thermal chillers to dry samples. For your testing, if you choose to use a low alarm pressure setpoint for the sample dryer pressure asa constant value in determining the amount of water removed from the emission sample, you may verify the accuracy of the low alarm pressure setpoint using good engineering judgment without following the linearity verification for sample dryer pressure. We recommend that you input a reference pressure signal above the alarm setpoint, decrease this signal until the low alarm trips, and verify that the alarm setpoint value is no more than 4 kPa above the reference value at the trip point. (e) When following procedures or practices that we incorporate by reference in § 1066 .1010, you must meet the linearity requirements given by the procedure or practice for any analytical instruments not covered under 40 CFR 1065.307, such as GC–FID or HPLC. § 1066. 140 Diluted exhaust flow calibration. (a) Overview. This section describeshow to calibrate flow meters for diluted exhaust constant-volume sampling (CVS) systems. We recommend that you also use this section to calibrate flow meters that use a subsonic venturi or ultrasonic flow to measure raw exhaust flow. You may follow the molar flow calibration procedures in 40 CFR 1065.340 instead of the procedures in this section. (b) Scope and frequency. Perform this calibration while the flow meter is installed in its permanent position, except as allowed in paragraph (c) of this section. Perform this calibration after you change any part of the flow configuration upstream or downstream of the flow meter that may affect the flow-meter calibration. Perform this calibration upon initial CVS installation and whenever corrective action does not resolve a failure to meet the diluted exhaust flow verification (i.e. , propane check) in 40 CFR 1065.341. (c) Ex-situ CFV and SSV calibration. You may remove a CFV or SSV from its permanent position for calibration as long as the flow meter meets the requirements in 40 CFR 1065.340(c) . (d) Reference flow meter. Calibrate each CVS flow meter using a reference flow meter such as a subsonic venturi flow meter, a long-radius ASME/NIST flow nozzle, a smooth approach orifice, a laminar flow element, or an ultrasoni

FAQs

What does § 1066.140 cover for CVS systems?

It describes calibration of flow meters used for diluted exhaust constant-volume sampling (CVS) systems, including conditions and options relevant to raw exhaust flow measurements.

When must the diluted exhaust flow calibration be performed?

Perform it with the flow meter in its permanent installed position, after changes to upstream/downstream flow configurations, upon initial CVS installation, and when corrective actions fail to resolve verification failures.

What linearity requirements apply to flow meters and specific measurements?

The section provides linearity criteria for flow meter linearity verification and specifies which temperature and pressure measurements to verify, along with accepted evaluation approaches in certain alarm-setpoint scenarios.

Sep 4, 2026

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