iso 5167, error calculation for orifice system

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iso 5167, error calculation for orifice system
in my system, orifice flow meter is installed at suction side of blower. following iso 5167, all requirements are satisfied except downstream distance. it is required at 4d but in our system it is 3.3d.
this orifice flow meter is used for anti-surge control of blower. it does not require high accuracy of flow meter. therefore, i should calculate error of our orifice system with downstream distance of 3.3d (not meet iso requirement)
i have read iso 5167, 5168 but still can not understand how to calculate error for this case. anyone knows about it, please instruct me.
thank you
check out our whitepaper library.
most head type flow meters address a "fully developed flow profile".  the standards for selecting orifice plate upstream and downstream diameters are based upon this requirement.  most of us would only suggest that the accuracy and repeatability would be dimenshed by non compliance with the recommendations.  some of the flow element manufacturers may be able to make predict with all of the specific size details.