Flow Meter Clibration

Hello just curious on how exactly is a flow meter in a vault on a main water pipeline supposed to get calibrated? Removing the flow meter for a bench calibration is out of the question. we have a flow meter that's reading incorrectly and i want to verify the accuracy but not quite sure how i should do this? what i had in mind was using a very accurate strap on flow meter (ultrasonic). This is a rose mount magnetic flow meter.

You are on the right track. This would be the way in which I would do the calibration.
http://au.flukecal.com/blog/flowmeter-calibration-five-best-practices-you-need-know

Regards,
Garry
http://www.accautomation.ca

Thanks!

I've had mixed success with strap on ultrasonic flow meters, so be aware of the constraints of pipe materials, straight pipe requirements, etc.

Depending on where the meter is in the system you might be able to get a quire accurate reading without other devices. For example, if the meter is at the main exit from your stand pipe or water tower you can simply shut off all pumps and measure the time it takes to drop the water level one foot. Then the volume of a one foot drop divided by the time is the flow rate.

Have you contacted the manufacturer for assistance?

Some vendors have an electronic box that measures the coil and electrode performance and compares the measured performance to factory original performance that has been 'saved' on flash memory or PROM in the flow meter. The box is used on-site for testing installed mags.

Although this type of certfication is not a flowstand calibration, many municipalities accept this type of recertification, given the difficulties in getting a large magtube in a vault to a flowstand and back again.

As to whether that model has the needed characterization parameters saved in its memory, you'd have to check with the vendor and see how Rosemount does its field certification of installed mags.

Clamp-on ultrasonics need a meter run length of straight pipe upstream and downstream for flow profile conditioning.

The internal condition of the pipe (scale, rust, hard water deposits) can influence the ability to get a reading and also affects any flow meter's calculated flow rate because the calculated flow rate is based on the assumption of a known, fixed pipe ID and that the pipe ID does not change, whereas it can changed over over time.

If you have some threaded or flange connections, of if you could install a hot tapped connection, then a pitot tube or annubar meter could work as well.

Ill go ahead and contact the manufacturer and see what they suggest. Giving this more thought, the flow meter is in a vault directly after our pump station, wondering if turbulence might be the culprit giving false readings of course, ill also try increasing the damping value.

the rosemont mag meters E series will actually do full verification which makes sure that the electrodes. the coil and the liner are all in good shape and thus don't need calibration . D series just requires money for the unlock code to do it. and older ones require full upgrade. a warped liner was my biggest issues with them cause by vacuum. then ocassionaly an open coil or shorted electrodes.

when it is a steady flow, you can fill a container with water, and then check if the amount is the same as measured.

Not so easy on >300mm diameter watermains!

(I had someone from our equivalent of the EPA suggest something similar for checking meter accuracy. I suggested he hold the bucket while I opened the scour valve on the 200mm main with 10 bar of pressure. ..)

The new Promag W 400 series from Endress & Hauser have a built in verification rig which will even produce a PDF with verification cert if you hook up with your laptop.

In saying that I also saw a meter get verified once but our flow balance was still wildly out. Found that the cables to two of the meters had been swapped by mistake, and since they had different diameters the meters were producing erroneous flow results. But as far as the test rig was concerned all was A-ok electronically!