Rerange orifice meters

[OilBoiler]

Hi everybody,

I have a question regarding orifice transmitter ranges. If you have a maximum dP range of 0-250 in H2O is there a common practice to design the plate so that the range is only 100 in H2O? In other words, would it affect accuracy if you instead range it for 175, 200, or even the 250 in H2O?

I need to re range current orifice meters and I need to increase the flow and I was wondering if there is a recommended maximum dP that we should design for. Thanks!

 

[ilan7]

Transmitter error ar part according to the range and part according to the URL (Upper Range Limit). But usually the numbers are low, compare to the Orifice (and pipe) uncertenties.
Lately the DP Transmitters rangability is increasing, when the accuracy is getting better: Normal accuracy is at the 0.075% with 1:40 rangability (Rosemount, SMAR, Yokogawa, etc). I do not think there is a problem with changing the transmitter range, just make sure:

1. Readings are inside the transmitter range
2. Flow is not chocked at the orifice.
3. There are 7-10 x pipe Diameter length of stright pipe before the Orifice and 3-5 after it.

Cheers

 

[m777182]

You can adjust your orifice to your dP transmitter or easily your transmitter to your orifice. When choosing an orifice you look for some optimal linear flow velocity, pressure loss, sometimes available space play the main role.Then you take appropriate dP transmitter.When nothing could be done with your dP transmitter then you redesign the orifice allowing for condition 2. and 3. of ilan7'th answer.
m777182

 

[INSTRUMEN]

For compressible fluid service, please ensure that DP range shall be lower than the 5.4% of the absolute upstream pressure for normal flow measurement (i.e. non custody meter application), for custody meter application it shall be 3.4%.

 

[jsummerfield]

Stated differently, the throw-down criteria for compressible fluids is that the dp in inch-water should not exceed the absolute pressure in psi. Otherwise, typically people start with 100-inch and increase as necessary. Exceeding 200-inch water is regarded as wasting horsepower. It is done in some modifications.

This is interactive with the flow element. Avoid a beta ratio, orifice plate bore/pipe id exceeding 0.7.



John