# RS Logix Flow Rate

• posted

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

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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

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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

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The setup is on a test rig. Just want the readout of flowrate & total in the plc program.

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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

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Google on "orifice plate flow calculator"

Using SLC5/03 & RS Logix.

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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

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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

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Thanks for that. With some mods to suit the application, I got it working.

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