home


    Page 1

    Page 2

    Page 3

    Back to 'tech. help'


    The sense and nonsense on Emission testers

    This article aims to dispell some of the myths that seem to be around emission testers.



    Article No. 33 Page 2/3

    		AVL 4000 BMW OEM testerclick for AVL 4000 emission tester info
    ...Continued.


    Light absorbsion of infrared light by CO, HC and CO2 gasses in the emissions

    Zero Calibration

    The IR light source needs to be of a calibrated intensity (brightness). If the intensity is not correct the IR light levels received are incorrect, so the displayed values will incorrect.

    The IR light source is current controlled, the higher the current the higher the light intensity and vice versa. During 'zero calibration' the current to the light source will be adjusted to achieve a stable and perfect light intensity at the receptors.

    During tester warm-up the exact same thing happens, The light source is 'switched on' and starts producing (IR) light. The receptors in turn need to warm up too. The intensity reading of the receptors is at first incorrect, but still they will adjust the current to the light source.

    The adjusting and readjusting of the light source intensity and receptor functionality during warm-up takes time. The tester should be left alone during this time.

    Simplified depiction of the zero calibration and warm-up procedure of the light source
    A = desired light intensity
    X = bandwidth of cheap tester
    Y = bandwidth of precise tester
    B = Warm-up duration cheap tester (e.g. 2 minutes)
    C = Warm-up duration precise tester (e.g. 15 minutes)



    During warm-up no emissions should be in the tester, therefore the tester will draw clean air from the back of the tester through an active carbon filter with a life span of about 24 months (if the tester is not parked besides cans of paint or petrol).
    The stabilising of the tester is important to get correct results, specifically if we are going to pass or fail vehicles as a result of the tester's indicated values.
    The warm-up period is determined by the gas bench (tester's internals) manufacturer and since almost all gas benches are sourced from only 3 or 4 different manufacturers in the whole world the warm-up time of all testers should be about the same….

    Sales people...

    Continued..

    Back to 'tech. help'

    Back to 'Welcome'