×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Flowmeter correction factor

Flowmeter correction factor

Flowmeter correction factor

(OP)
Hello,

I'm not an instrument guy but I have a question concerning the application of correction factors to flow measurements.
During actual plant operation, operating conditions may be significantly different from design conditions (density for liquids, and T, P, Z and molecular weight for gases).
Therefore, the measured flowrates should be corrected to account for the measured process conditions.

I was wondering if the REFERENCE CONDITIONS used in these corrections shall always be equal to the design conditions (vendor data sheet) or if it is possible to redefine them.

For exemple, suppose a gas flowmeter had been designed with a molecular weight of 10 and that the actual measured molecular weight is closer to 25. For sake of simplicity, let's assume actual and design T and P are identical.
Is it sensible to redefine the reference molecular weight to a value close to the actual molecular weight, let's say 20 (so that the correction factor is equal to the square-root of 25/20)?
Or shall we let the reference molecular weight equal to the design molecular weight (from the data sheet) because the primary element had been designed with a molecular weight of 10 (so that the correction factor is equal to the square-root of 25/10)?

In the case it is recommendable to modify the reference conditions, shall we then recalibrate or recalculate the flowmeter accordingly?

Hope the description of my query is clear enough.

"We don't believe things because they are true, things are true because we believe them."

RE: Flowmeter correction factor

Why not just rerun the meter calculations at the actual (now) MW of 25?

If that's not possible for whatever reason, I'd just use the original meter factor (calculated for a MW of 10) and then correct it using the square root ratio of the MW as a quick correction.  However, that's not going to capture other meter factors which, to varying degrees, will also be affected by the change in MWs.

That correction approach is true for all dP style meters I believe, for other meters if you aren't talking about an orifice type meter, the correction factor (eg thermal) could be different.  I likely should know that but I don't.

RE: Flowmeter correction factor

(OP)
What do you ean by "rerun"?

"We don't believe things because they are true, things are true because we believe them."

RE: Flowmeter correction factor

Take your existing orifice meter, max dP and gas properties to calculate the maximum meter reading (assuming it's an orifice meter).  Then you can use the actual meter dP to estimate the flow.

Same process as if you were sizing the meter today or did I misunderstand something?

RE: Flowmeter correction factor

What kind of meter you using? Is it a orifice/dP?

RE: Flowmeter correction factor

(OP)
Yes, an orifice meter.

"We don't believe things because they are true, things are true because we believe them."

RE: Flowmeter correction factor

In this day and age just use a computer to calculate the flowrate every 1 second with live inputs. A stand alone unot or a subroutine in most all plc or dcs.  

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources