D/P Level Trasmitter DP per static pressure

[Warisa]

Hi all

I just read some book from IOGP what I have a question to the statment mentioned in this book is below

Electronic DP level system replaces the long lengths of oil‐filled capillary and impulse piping with an electrical
wire that is immune to temperature induced effect as well as the lengthy capillary. This means that it will be
possible to get an accurate measurement over a large range of ambient temperatures without fill‐fluid
density or volume changes affecting the reading. High and low pressure measurements are fully
synchronized to ensure that the differential pressure measurement is accurate.
If the ratio between the DP pressure and the vessel static pressure is (DP/Static) < 1/10 the impact on the
accuracy will be non‐negligible.
The effect of a static pressure on both side of a non‐electronic DP system implies a drift that needs to be
compensated. Electronic DP system calculates and compensates the pressure effect directly without specific
calibration.

The highlight in red made me a little bit confuse , who is expert and familiar in this measuring method , please explainmore and give me some example would be appreciated.

I'm not sure the exactly reason why ? T_T

Thank you so much <3

 

[themoke]

Hi,

Let me first state that I have no direct experience with these electronic dp devices. However, I believe the issue here is that with the electronic system you have two gauge pressure sensors, each having an accuracy as some percentage of span. When the static pressure is much larger than the dp you are interested in, your span will be a large, resulting in a large amount of inaccuracy when compared with the dp sensor counterpart where your span can be as tight as the actual level you are interested in.

Cheers,
Mike H.

 

[roydm]

I think Mike H pretty much nailed the problem.
One I am familiar with is measuring the interface between two fluids of quite similar SG
With a DP cell, diaphragm seals and capillaries it's very temperature sensitive.
The dual gauge pressure method is also effected by ambient temperature even though the static pressure is only about 10 psig.
Differential bubble tubes with a DP cell are least effected but many consider this too crude.