Where this general practice comes from Orifice Plate Turndown ratio The limitation of the DP type flow meter using orifice isnt comes from the beta ratio limitation of the flow orifice plate nor any other flow orifice plate dimension.In simplify concept we can calculate the orifice flow rate by: Qm C x (Differential Pressure)0.5 Where, Qm: Flow rate C: Meter Constant Differential Pressure: differential pressure across flow orifice plate From the above equation we know that the flow rate is proportional to the square root of the differential pressure.Basically the differential pressure transmitter it self can have a turndown ratio up to 100:1 but the square root extraction limits its capability in the upper range only.
See below calculation example that illustrates the increasing of error reading when the turndown ratio is below 3:1. Example of Orifice Flow Meter Error Reading Calculation From the above example, we know that the error reading (after perform the above square root calculation) is increasing along with the flow rate decreasing. The error reading is exceeding 0.5 when the flow rate is lower than 2500 lm. Let set this flow rate as our minimum flow rate since the flow rate measurement is having high error below this point. If we look further, the 2500 lm minimum flow and 7500 lm maximum flow is correspond to the 3:1 turndown ratio. This is where the 3:1 turndown ratio is applied in our general practices. If we insist to have minimum flow let say 1000 lm then we will have a turndown ratio 7.5:1. This will lead us to get an error reading of 2.8 which means a very bad measurement accuracy. Thus some engineer usually simply use a 3:1 turndown ratio as their rule of thumb to decide whether they will use DP type flow orifice plate flow meter or not. If the required turn down is higher than 3:1, then it will be better if we use another type of flow meter even though it is possible to have such higher turn down ratio by installing a parallel DP type flow orifice plate flow meter with a split range configuration. I dont have any reason regarding this except the parallel configuration will give us a high cost of material procurement. Orifice Plate Flow Calculator Full Scale OfArticles You May Like: Flow Meter Turndown Ratio Restriction orifice versus Orifice Instrument Turndown Ratio Flumes Flow Measurement Rotameter Working Animation Share With Your Friends Facebook Twitter LinkedIn Pinterest Email WhatsApp Previous Article Conductivity Analyzers Interview Questions Answers Next Article Interview Questions on Differential Pressure Flow Transmitter Related Articles What is Variable Area Flow Meter S Bharadwaj Reddy January 30, 2018 June 25, 2019 Mass Flow Meters S Bharadwaj Reddy March 3, 2017 June 27, 2019 Oval Gear Flow Meters Animation S Bharadwaj Reddy June 10, 2016 July 21, 2019 Flow Measurement Objective Questions S Bharadwaj Reddy January 23, 2017 April 21, 2019 Turbine Flow Meter Installation Procedure S Bharadwaj Reddy March 12, 2019 June 20, 2019 What is Positive Displacement Flow Meter S Bharadwaj Reddy February 2, 2018 June 24, 2019 1 comment Andy January 23, 2017 at 4:09 pm Nice article, however if the full scale of the transmitter is 200 inH2O and the transmitter accuracy is 0.1 of full scale, is the error in pressure measure not - 0.2 inH2O rather than 0.1 Reply Leave a Comment Cancel Reply Save my name, email, and website in this browser for the next time I comment. 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Well assume youre ok with this, but you can opt-out if you wish. Accept Read More X What is an Orifice Meter Flow Measurement An orifice meter is a conduit and a restriction to create a pressure drop. A nozzle, venturi or thin sharp edged o Flow Measurement Orifice Plate Turndown ratio X In Line Flow Switch Working Principle Animation Animation In Line Flow Switch are comprised of two main assemblies: the housing and the shuttle assembly.
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