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  • MVP 2023

OK - so you've got the 20 mm ID unit where 4/20 mA = 5 to 85 l/min: 


The -RA22 is the high resolution analog input board, where 0 - 20 mA = 0 to 16384 counts.  4 mA = 3277 counts, so your 4/20 signal will be spread over 13,107 counts.  

If you use a virtual decimal place at 0.xx, you can scale your flowrate input to 5.00 to 85.00 l/min.

The -RA22 has four analog inputs which are dedicated to input type.  AI 0 and AI1 are for thermocouples and 100 ohm RTDs, and AI 2 and AI 3 are for 0-10VDC or 4/20 mA.  You'll need to set the jumpers inside the unit to select the 4/20 input.  I'd recommend connecting your flowmeter to AI 2.

Your linearization block can be set up like this:



I've attached a program showing this.  How often you sample it and the math to totalize flow is up to you.  Since your input flowrate can be up to 8500, I'd recommend doing your math in MLs as you will quickly overrun the maximum value of an MI which is 32,727.

To answer your question, your precision is 0.01 l/min.

Joe T.

Flowmeter scaling JT.vlp

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