40 C.F.R. § 51 app D to Subpart S of Part 51
(I) Steady-State Test Exhaust Analysis System
(a) Sampling system -
(1) General requirements. The sampling system for steady-state short tests shall, at a minimum, consist of a tailpipe probe, a flexible sample line, a water removal system, particulate trap, sample pump, flow control components, tachometer or dynamometer, analyzers for HC, CO, and CO2, and digital displays for exhaust concentrations of HC, CO, and CO2, and engine rpm. Materials that are in contact with the gases sampled shall not contaminate or change the character of the gases to be analyzed, including gases from alcohol fueled vehicles. The probe shall be capable of being inserted to a depth of at least ten inches into the tailpipe of the vehicle being tested, or into an extension boot if one is used. A digital display for dynamometer speed and load shall be included if the test procedures described in appendix B to this subpart, paragraphs (III) and (V), are conducted. Minimum specifications for optional NO analyzers are also described in this appendix. The analyzer system shall be able to test, as specified in at least one section in appendix B to this subpart, all model vehicles in service at the time of sale of the analyzer.
(2) Temperature operating range. The sampling system and all associated hardware shall be of a design certified to operate within the performance specifications described in paragraph (I)(b) of this appendix in ambient air temperatures ranging from 41 to 110 degrees Fahrenheit. The analyzer system shall, where necessary, include features to keep the sampling system within the specified range.
(3) Humidity operating range. The sampling system and all associated hardware shall be of a design certified to operate within the performance specifications described in paragraph (I)(b) of this appendix at a minimum of 80 percent relative humidity throughout the required temperature range.
(4) Barometric pressure compensation. Barometric pressure compensation shall be provided. Compensation shall be made for elevations up to 6,000 feet (above mean sea level). At any given altitude and ambient conditions specified in paragraph (I)(b) of this appendix, errors due to barometric pressure changes of ±2 inches of mercury shall not exceed the accuracy limits specified in paragraph (I)(b) of this appendix.
(5) Dual sample probe requirements. When testing a vehicle with dual exhaust pipes, a dual sample probe of a design certified by the analyzer manufacturer to provide equal flow in each leg shall be used. The equal flow requirement is considered to be met if the flow rate in each leg of the probe has been measured under two sample pump flow rates (the normal rate and a rate equal to the onset of low flow), and if the flow rates in each of the legs are found to be equal to each other (within 15% of the flow rate in the leg having lower flow).
(6) System lockout during warm-up. Functional operation of the gas sampling unit shall remain disabled through a system lockout until the instrument meets stability and warm-up requirements. The instrument shall be considered "warmed up" when the zero and span readings for HC, CO, and CO2 have stabilized, within ±3% of the full range of low scale, for five minutes without adjustment.
(7) Electromagnetic isolation and interference. Electromagnetic signals found in an automotive service environment shall not cause malfunctions or changes in the accuracy in the electronics of the analyzer system. The instrument design shall ensure that readings do not vary as a result of electromagnetic radiation and induction devices normally found in the automotive service environment, including high energy vehicle ignition systems, radio frequency transmission radiation sources, and building electrical systems.
(8) Vibration and shock protection. System operation shall be unaffected by the vibration and shock encountered under the normal operating conditions encountered in an automotive service environment.
(9) Propane equivalency factor. The propane equivalency factor shall be displayed in a manner that enables it to be viewed conveniently, while permitting it to be altered only by personnel specifically authorized to do so.
(b) Analyzers -
(1) Accuracy. The analyzers shall be of a design certified to meet the following accuracy requirements when calibrated to the span points specified in appendix A to this subpart:
| Channel | Range | Accuracy | Noise | Repeatability |
| HC, ppm | 0-400 | ±12 | 6 | 8 |
| as hexane | 401-1000 | ±30 | 10 | 15 |
| 1001-2000 | ±80 | 20 | 30 | |
| CO, % | 0-2.00 | ±0.06 | 0.02 | 0.03 |
| 2.01-5.00 | ±0.15 | 0.06 | 0.08 | |
| 5.01-9.99 | ±0.40 | 0.10 | 0.15 | |
| CO2, % | 0-4.0 | ±0.6 | 0.2 | 0.3 |
| 4.1-14.0 | ±0.5 | 0.2 | 0.3 | |
| NO, ppm | 0-1000 | ±32 | 16 | 20 |
| 1001-2000 | ±60 | 25 | 30 | |
| 2001-4000 | ±120 | 50 | 60 |
(2) Minimum analyzer display resolution. The analyzer electronics shall have sufficient resolution to achieve the following:
| HC | 1ppm HC as hexane. |
| CO | 0.01% CO. |
| CO2 | 0.1% CO2. |
| NO | 1ppm NO. |
| RPM | 1rpm. |
(3) Response time. The response time from the probe to the display for HC, CO, and CO2 analyzers shall not exceed eight seconds to 90% of a step change in input. For NO analyzers, the response time shall not exceed twelve seconds to 90% of a step change in input.
(4) Display refresh rate. Dynamic information being displayed shall be refreshed at a minimum rate of twice per second.
(5) Interference effects. The interference effects for non-interest gases shall not exceed ±10 ppm for hydrocarbons, ±0.05 percent for carbon monoxide, ±0.20 percent for carbon dioxide, and ±20 ppm for oxides of nitrogen.
(6) Low flow indication. The analyzer shall provide an indication when the sample flow is below the acceptable level. The sampling system shall be equipped with a flow meter (or equivalent) that shall indicate sample flow degradation when meter error exceeds three percent of full scale, or causes system response time to exceed 13 seconds to 90 percent of a step change in input, whichever is less.
(7) Engine speed detection. The analyzer shall utilize a tachometer capable of detecting engine speed in revolutions per minute (rpm) with a 0.5 second response time and an accuracy of ±3% of the true rpm.
(8) Test and mode timers. The analyzer shall be capable of simultaneously determining the amount of time elapsed in a test, and in a mode within that test.
(9) Sample rate. The analyzer shall be capable of measuring exhaust concentrations of gases specified in this section at a minimum rate of twice per second.
(c) Demonstration of conformity. The analyzer shall be demonstrated to the satisfaction of the inspection program manager, through acceptance testing procedures, to meet the requirements of this section and that it is capable of being maintained as required in appendix A to this subpart.
(II) Steady-State Test Dynamometer
(a) The chassis dynamometer for steady-state short tests shall provide the following capabilities:
(1) Power absorption. The dynamometer shall be capable of applying a load to the vehicle's driving tire surfaces at the horsepower and speed levels specified in paragraph (II)(b) of this appendix.
(2) Short-term stability. Power absorption at constant speed shall not drift more than ±0.5 horsepower (hp) during any single test mode.
(3) Roll weight capacity. The dynamometer shall be capable of supporting a driving axle weight up to four thousand (4,000) pounds or greater.
(4) Between roll wheel lifts. These shall be controllable and capable of lifting a minimum of four thousand (4,000) pounds.
(5) Roll brakes. Both rolls shall be locked when the wheel lift is up.
(6) Speed indications. The dynamometer speed display shall have a range of 0-60 mph, and a resolution and accuracy of at least 1 mph.
(7) Safety interlock. A roll speed sensor and safety interlock circuit shall be provided which prevents the application of the roll brakes and upward lift movement at any roll speed above 0.5 mph.
(b) The dynamometer shall produce the load speed relationships specified in paragraphs (III) and (V) of appendix B to this subpart.
(III) Transient Emission Test Equipment [Reserved]
(IV) Evaporative System Purge Test Equipment [Reserved]
(V) Evaporative System Integrity Test Equipment [Reserved]
40 C.F.R. 51 app D to Subpart S of Part 51