To ensure the accuracy and reliability of on-board OBD(On-Board Diagnostics)acquisition terminals and improve the effectiveness of exhaust emission monitoring and overstandard screening for heavy-duty diesel vehicles,a digital metrology method is proposed.This paper introduces the definition,application,and current metrological status of on-board OBD acquisition terminals.It elaborates on the calibration method for these terminals and demonstrates their metrological characteristics from two aspects:determination of maximum permissible error and uncertainty evaluation.Three conclusions are drawn from the demonstration:the maximum permissible error of real-time engine data flow from the calibration device is set according to the data flow precision specified in the protocol,and the maximum tolerance of the on-board OBD acquisition terminal is set at twice the tolerance of the calibration device;the uncertainty introduced by the real-time engine data flow from the calibration device is Urel=1 × 10-6,k=√3,and the uncertainty evaluation of the on-board OBD acquisition terminal meets the quantity transfer requirement of U ≤MPEV/3;test results show that the indication error of the on-board OBD acquisition terminal does not exceed the maximum permissible error,the metrological performance requirements are reasonable,and the calibration method is highly operable.
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