RS Logix Flow Rate


Using SLC5/03 & RS Logix.
I have a pump that pumps water at about 5 litres a minute. The flow is
measured from a DP cell across an orifice plate. The 4-20 mA signal from the
DP Cell is linearised by the square root function in the plc program.
How can I take the linearised flow signal and give me a readout of pump
flowrate and total flow within the plc. I only want the readings in the RS
logix program and not to an external device. The readings need to be in
engineering units litres per minute & total litres.
TIA
Reply to
BIGEYE
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If the formula really linearizes the curve -- in practice, not just in theory -- then all you need to do to get the rate is multiply by an appropriate scale factor. Determine that factor experimentally.
Total flow is obtained by integrating flow rate over time. For suitably short intervals, the accumulated sum of the flow rates at the start of each interval gives the total flow or a number proportional to it. You can calculate the proportionality constant from the calibrated rate and the measurement interval.
Jerry
Reply to
Jerry Avins
If I understand your question correctly----To get instaneous flow rate is there any reason why you can't run a calibration of flow vs Delta P on a bench (vs doing it analytically) and then make a table of Delta P vs Flow. Input Delta P into this look up table to get flow. MLD
Reply to
MLD
The setup is on a test rig. Just want the readout of flowrate & total in the plc program.
Reply to
BIGEYE
Have used non linear flow sensors as well Delta P across an orifice many times and got a flowrate readout on both a digital counter display as well as on a transient data tape and print out. Never had the need to know the absolute total flow. MLD
Reply to
MLD
Google on "orifice plate flow calculator"
formatting link
is one of the results, just scale your linearized DP to flow
Reply to
me
To get the total flow, you will have to integrate the flow rate over your period of interest to accumulate the volume.
Mark Walsh snipped-for-privacy@rogue-engr.com
Reply to
Mark
SOR XIO T4:0/DN TON T4:0 0.01 50 0 EOR SOR XIC T4:0/DN BST MUL N7:0 0.6105 F8:0 NXB DIV F8:0 120.0 F8:1 NXB ADD F8:1 F8:2 F8:2 BND EOR
BIGEYE, the above logic is from a PLC5 RSLogix, you might be able to paste it into your SLC RSLogix. T4:0 1/2 sec one shot timer N7:0 Raw analog unscaled F8:0 Flow rate scaled to engineering units F8:1 1/2 sec flow total F8:2 Totalized value
If you have questions jen_tra1 snipped-for-privacy@yahoo.com
Reply to
Haas
Thanks for that. With some mods to suit the application, I got it working.
Reply to
BIGEYE

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