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Friday, July 19, 2019
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Changing Fluid Type in DP Wet Legs
What could be the results if I change the sg of fluid in both high and low impulse lines of a DP level without re-ranging?

Hi all,

What will happen if I change the sg of fluid in both high and low impulse lines of a DP level without re-ranging?

If I pumped up high and low wet legs with glycerin when the cal has been set up for water to be in both high and low legs, would it read out or would the error equal out because both sides are beings affected by the different SG fluid?

I'd love to see the math of it's not too difficult for someone.

Cheers.

For flow meters with equal length legs, no change.

For level measurement, you have to include the density for both measurement legs.

Bernoulli's equation covers it,

deltaP = density1*Leg1-density2*Leg2

It is all handbooks and no doubt the internet.

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Are you using the term 'wet leg' for a remote seal DP transmitter? Probably not, one doesn't 'pump up' seal capillaries without some dedicated effort (vacuum evacuation and backfill).

It isn't clear to me how you have a wet leg on the level's process bottom side that does not pollute itself with the process liquid.

Changing a conventional tank level reference wet leg fill fluid for one with a different density will definitely change the reference leg's applied pressure and hence, the reference value.

For DP transmitter with dual remote seals, a change in the capillary fill fluid density affects the both LRV and URV values.

See the diagram here for the DP dual remote seal LRV/URV calculation:

https://s15.postimg.cc/f8dfego8r/illustrated_calculations_for_LRV_and_URV_remote_seal_DPs.jpg