What Flow Rate?

We have a centrifugal pump that pumps at about 20 litres/sec. I need to install a mag flow meter on the discharge side with an analogue output. The mag flow meter will need to be programmed to the appropriate range, should I program for 0 to 20 litres/sec or perhaps 0 to 30 litres/second would be more appropriate.

What about an application where the flow rate of a pump is unknown and can't be determined. If a flow meter was left at its factory default setting of whatever, how accurate would the actual reading be, assuming the flow rate of the pump was not in excess of the full range factory setting of the flow meter.


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Your 20 lps flow rate puts you into a 3"/75-80mm flow tube. From one of my spec sheets, the maximum flow rate for a 3" meter is 800 gpm, which converts to 50.47 lps. Unless otherwise specified, the factory uses the maximum flow rate as the default setting for the transmitter analog output signal. You can program the output for any range you like, but rounding it to a whole number, such as 40, is simpler to manage.

Generally speaking, if you pick a flow meter that's the same size as your pump discharge, the meter range should be adequate for the pump flow unless you get into a low head / high flow / off the pump curve situation. The analog output range setting should not affect the accuracy of the remote flow display. You can lose resolution by having more digits in the range than the digital/analog conversion includes, i.e. 0-8000 gpm with 12 bit conversion (0-4095 counts), but that's a different issue.


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Mike Lamond

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