Hedland Flow Meter Calculating Correction Factors for Different Fluid Conditions
Standard scales for liquid applications are calibrated in GPM and LPM using three standard conditions: 0.876 specific gravity for petroleum based fluids, 1.0 s.g for water and water based fluids and finally, 1.18 s.g. for phosphate ester based fluids.
As with most flow meters utilizing an inferred measurement technology, any change to fluid properties, (viscosity and/or specific gravity) can have an effect on meter accuracy. Thanks to its unique design, Hedland VA Meters remain accurate over a wide range of fluid viscosities. High flow models typically provide good accuracy over a viscosity range of 40 to 500 SUS (4.2 to 108 cSt).
But, changes to fluid density (Specific Gravity) from the published standards for Hedland's VA Flow Meters has a proportional effect on meter's accuracy. To counter this, special scales and/or correction factors can be supplied if these changes decrease the meters accuracy beyond application limits. While most customers opt for a correction factor to use with a stock meter calibrated using standard conditions, very few understand how the Correction Factors (C/F) are calculated.
Calculating Correction Factor
Corrections for more or less dense fluids can be made to Hedland's standard scales using the following correction equations. There are just two; One for measuring alternate fluids in a flow meter originally calibrated for water measurement and a second for measuring alternate fluids in an Oil Flow Meter.
Simply choose the correct formula based on your existing flow meter. Divide 1.0 (for Water Meters) or 0.876 (for Oil Meters) by your fluid's Specific Gravity, take the square root of the result and multiply that times the given flow rate. Sounds simple enough, but you still may want to go through the individual steps shown below just to be sure.
For example... Let's calculate the conversion factor for measuring Liquid Propane (LPG) with a Petroleum Meter at 28.5 GPM.
Step 1: Using the table below, locate the specific gravity of LPG… Answer: 0.51
Step 2: Since we're utilizing a petroleum meter in this example, we'll use the petroleum formula (above).
Step 3: Divide 0.876 by 0.51 = 1.72
Step 4: Calculate the square root of 1.72 to determine the correction factor (1.31)
Step 5: Finally, to determine the actual flow rate of water being measured in a petroleum meter, simply multiply the scale reading by the correction factor. In this instance, that would be 28.5 gpm times 1.31 (C/F) which equals 37.3 GPM of water.
Fluid Properties & Correction Factors
Correction factors for 27 fluids typically measured with a Hedland VA Meter are shown in the tables below. If your fluid is not included in this chart, I'm pretty sure that if you've read this far, you can do that math and figure it out yourself! All you'll need to know is the specific gravity and what type of meter (Water or Oil) you're doing the conversion for.