Remote Seal Head Correction Calculator
The fill fluid in a remote seal capillary has weight. Calculate the zero offset it causes when the transmitter is mounted above or below a single seal, or the elevation caused by the vertical distance between two seals on a DP transmitter.
- Offset = SGfill × ρwater × g × h = 0.93 × 9806.65 × 2 = 18,240 Pa
- Subtract this from the reading, or apply it as a zero trim
Fill Fluid Head Effect
Remote seals transmit pressure through an incompressible fill fluid. Any vertical difference between seal and transmitter creates a static head that the transmitter sees as pressure.
Two seals: ΔPshift = −SGfill × ρwater × g × H
Here h is the height of the seal above the transmitter and H the vertical distance between the two seals of a DP system.
Worked example
A DP level transmitter has seals 3 m apart filled with silicone oil of SG 0.93. The LP capillary adds 0.93 × 3000 = 2790 mmH₂O, so the range shifts by −273.6 mbar. A level range of 0 to 2.5 m water then becomes −273.6 to −28.4 mbar.
Frequently Asked Questions
Does the transmitter height matter on a two seal DP system?
No. Both capillaries rise or fall by the same amount when the transmitter moves, so the effect cancels. Only the distance between the seals matters.
What fill fluid SG should I use?
Use the value from the seal datasheet at operating temperature. Common silicone fill fluids are roughly 0.93 to 1.07 depending on grade.
Can I correct the head effect with a zero trim?
For a single seal, yes: a zero trim or lower range adjustment removes the fixed offset. For DP level, enter the shifted LRV and URV in the transmitter instead.
Learn more on the blog
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