Magnetic flowmeter calibration 2

[btrueblood]

Our company owns a 12" magnetic flowtube and transmitter from the Rosemount company, but it's pretty old. The meter is installed in a flow test system for cast iron valves, and may be subject to erosion from sand and rust particles. We (I) am now in the process of trying to update the calibration for the meter, which becomes pretty expensive for this size meter. Rosemount advertises their current models of mag meters as having the capability to be recalibrated in-line (essentially via software, by measuring the circuit characteristics at a no-flow condition).

Questions -

1) has anybody used this recalibration system, does it really work? Does it account for wear and/or filming on the meter i.d.?

2) Do you know if the in-line calibration can work for older models of flowtubes/meters, and/or other manufacturers' models; does this require the transmitter to be changed to the Rosemount version?

Thanks for any help/advice.

 

[dcasto]

I've not used this type meter, but logic expanded from all velocity based meters says this: They should be able to zero the meter and get the no flow lag time as they state. When flow is established, the probe will now measure the velocity based on the time lag as compared to the time lag with no flow. BUT because the meter reads average or combination of spot velocities, it knows nothing about area nor the flow profile. All custody transfer meters would require a prover loop to establish the flow profile and adjust for variations in flow area. You may need to have a flow conditioner too.?

 

[btrueblood]

Thanks dcasto, that's what I'm thinking too - without a prover loop (or offline calibration to a traceable standard) then there is no traceability to NIST, therefore no "real" or certifiable calibration.

FYI, that's what the meter manufacturer eventually said too, they can calibrate the transmitter, and tell you whether they think the system (meter+tube) is out of cal., but it's not a true calibration.

 

[hacksaw]

Sounds like you need to inspect the pipe first, clean it and do a dimensional check of the meter and the pipe.

Given the way a magmeter works the transmitter check is pretty good, but traceability requires flow proving. Just spend the money to have a flow prover certify the installation. Or, just remove the meter and return it to a flow test facility (Rosemount has one) for flow testing and calibration.

In-house checks are possible and accuract if you have the tankage, but not certifiable. If you were certifying flow measurement devices accuracy would be a real issue, but valves? What are your flow accuracy requirements for the valve test +/- 5%?

There are a half dozen other approaches that are more or less time consuming and even more expensive.

 

[Golestan]

Hi,
Yoou can also send the meter to the University of Utah-water research lab, where they have a NIST setup and measurung tank for large diameter meter calibration.
Regards,

 

[btrueblood]

"In-house checks are possible and accuract if you have the tankage, but not certifiable. If you were certifying flow measurement devices accuracy would be a real issue, but valves? What are your flow accuracy requirements for the valve test +/- 5%?"

Well...a) we can certify a prover (i.e. a tank) volume pretty accurately (well below 0.5%), with traceability to NIST, using various techniques...and timing, if done electronically on narrow segments of vertical tanks, with fairly smooth flow profiles, can be awfully accurate too. We've gone this route and established a NIST-traceable calibration to within +/-0.5% on volume flow.

But, yes, it gets expensive and time consuming to do this. That's why the idea of "calibrate in place" appealed to the boss; Rosemount advertises that its transmitter calibration qualifies as a flowmeter cal. for several gov't. agencies. I buy the premise, but as noted above, it ain't traceable so it ain't calibrated.

b) Our valves act a bit like flowmeters, but yes, +/-5% is all we guarantee; we want to certify to within 1-2%. And yeah, I can certify the meter about a dozen different ways, but it all comes down to $ and time.

Golestan, there a lots of places who can calibrate a meter, but thanks anyways for the tip.

Thanks for the help/suggestions, good discussion.