Digital Measurement Methods of OBD Diagnostic Apparatus for Motor Vehicle Emissions Inspection

To guarantee the accuracy and reliability of the measurement value of the diagnostic apparatus of On-Board Diagnostics (OBD) for motor vehicle emission inspection, and to enhance the metrological technical support for motor vehicle emission supervision, a digital measurement method was proposed. Firstly, the definition, composition and application overview of OBD diagnostic apparatus for motor vehicle emission inspection were introduced, and the current status of digital metrology was elaborated. The digital measurement method of OBD diagnostic apparatus for motor vehicle emission inspection was discussed, covering aspects such as real-time data stream calibration methods, calibration device traceability methods, and uncertainty evaluation. Finally, three conclusions were obtained through the demonstration: (1) the proposed measurement method aligns with the actual working conditions of OBD diagnostic apparatus, which is scientific, reasonable and operable; (2) the reasonableness of the traceability method of the calibration device is demonstrated by the uncertainty analysis of the standard value of the data flow written in the calibration device, the formulation of the physical indexes among the diagnostic connectors' pins under different protocols, and the reading test of the standard OBD test device, and the real-time data flow error measurement results are given after the evaluation; (3) the uncertainty of the measurement result of the data flow indication error was given, which can meet the requirements of the volume transmission.