how to decide the calibration range for DP flow transmitter while preparing Data sheet

I am new to preparing Instrument Datasheet for DP Flow transmitter. I have process data like Flow, Design Press & Temp, Operating Press & Temp, Density, viscosity. Using Orifice with tap flange for DP measurement. I am not sure how to decide the calibration range for DP flow transmitter now in inches of water column. Also I am confused while seeing some samples like 0 to 500 inWC while some shows -250 to +250 inWC. how to decide that now!
Thanks in advance.
 
You don't guess at a DP value.

All that data you're entering is used to calculate either the DP at a max flow rate or the flow rate at a max DP. I call it 'sizing' a primary flow element. Each primary flow element has a Bernoulli calc associated with it with its K factor. Most vendors offer to 'size' the element (they have computer software to crank them out), so a flow element comes with a 'sizing sheet' that lists the design criteria and results of calculation.

What you need in order to get DP at the maximum flow rate is to run the calculation yourself or take the max DP value and max flow rate value from the sizing sheet that the vendor or engineering firm runs for you.

The sheet below shows the design data for 3.5" line for Ethane. The target DP is 100"wc drop at the maximum flow rate calculated at 648.2 GPM

blacked out customer data, Ethane 0.5in line.JPG

For the example application above, the DP transmitter would be configured for
- square root extraction
- LRV = 0.0"w.c. DP = 4.0mA and the receiver would be configured for 4.0mA = 0.0 GPM flow rate
- URV = 100.00"w.c DP = 20.0mA and the receiver would be configured for 20.0mA = 648.2 GPM flow rate
 
Thanks David.
Let me know I am following the right procedure to prepare FE & FT datasheet.
I took all the process data for FE sizing in instrucalc. Now it asks for what to calculate out of three options i.e. flowrate, DP range or Beta ratio. I selected Beta ratio here.
Now only option i have is to do trial and error by filling standard DP values like 250, 500 inWC etc. to check if the beta ratio is between 0.3 to 0.7.

My second query is that once i am sure that DP range is 500inWC, then how do I decide if the calibration range shall be '0 to 500 inWC' or '-250 to +250 inWC'.
 

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Thanks David.
Let me know I am following the right procedure to prepare FE & FT datasheet.
I took all the process data for FE sizing in instrucalc. Now it asks for what to calculate out of three options i.e. flowrate, DP range or Beta ratio. I selected Beta ratio here.
Now only option i have is to do trial and error by filling standard DP values like 250, 500 inWC etc. to check if the beta ratio is between 0.3 to 0.7.

My second query is that once i am sure that DP range is 500inWC, then how do I decide if the calibration range shall be '0 to 500 inWC' or '-250 to +250 inWC'.
For Flow Transmitter LRV always Zero. First you Decide the orifice bore, then come to transmitter Dp range selection.I hope its the best way to do
 
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