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From: [email protected]
To: <[email protected]>
Subject: APPS: BS&W meters

Hi Folks,
We have several BS&W meters installed in the crude oil discharge to measure the water content in the water. The meters are capable to measure 0-3% and it outputs 4-20mA. These meters operation bases on capacitance principle. If dry oil passes through the probe, it outputs 4 mA and 20 mA if the oil has 3% of water. The probe card has a
calibration card so the calibration (zero/span) can be adjusted.

The meter full range calibration is achieved by filling the probe volume with a solution of 3% water contents. The problem is that the
calibration should be done quickly otherwise the water gets deposits so the solution dialectric changes and the calibration fails. Stirring the solution during calibration, helped but if bubbles are formed then calibration fails.

Anybody experienced with similar problem or could suggest any way to calibrate the meters?

Thanks,
Jose Chong

 

Hi Jose,
I think you are refering to the "Hydril".
I hope the probes are designed to nullify these effects. Also the capacitance is measured along a cylinder (parellel) and hence doesn't really
affect due to air bubbles. The capacitance adds and the ones introduced by dielectric air is so so small compared to that of the liquid is negligible and will be well within the accuracy spec. Since all capacitances are added, the water and oil dielectric, even if treated (not an emulsion) separately will only add....!
Ramesh

 

Ramesh,
Yes the sensing device is Hydril.
The probing range is 0 - 3% to 4 - 20mA which is indeed sensitive to strange particules in the liquid. You are correct when saying the air particles generated during the stirring is negligible. Normally the electrode has trimmers to adjust the capacitance errors. The Hydril signal is fed into Scada where the data is stored for the last 15 days for monitoring. Daily the product is sampled twice for better results
from the labortory.
Jose Chong