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Example of rate and volume from a 4-20 mA flow meter
Application:
Transmit flow rate in GPM to three decimals and totalized volume in gallons to two
places from a 4-20 mA flow meter calibrated so that 4 mA = 0 GPM and 20 mA = 18.756 GPM.
Do not totalize reported flow rates below 0.050 GPM, as these are deemed to be noise.
Solution:
•
Under Input+Display tab, set Signal Input Mode to “VF 4-20 mA”, Function to “A, A Total”,
Cutoff Value to 00.050, Cutoff Enable to Enabled, and Power-On Total to “Restore Total” (to
retain total in event of a power failure).
•
Under Scaling tab for “VF 4-20 mA A Rate”, set Decimal Point to three places. If “Scale,
Offset” scaling method is selected, set Scale 1 to +1.17225 (which is 18.756 GPM / 16.000
mA), and set Offset 1 to -4.689 GPM (so that 4 mA will read 0 GPM). If Coordinates is
selected as scaling method, simply enter Low In, Low Read, High In, High Read as shown.
•
Under Scaling tab for “A Total”, the time integration interval 1 sec. Enter 0.3126 Scale 2
(which is rate in gallons/sec) and +0000.00 for Offset 2 in gallons if you want the starting
volume to be 0 gallons since last reset.