Servo Level Measurement

Servo Level Measurement

Servo level measurement is a high-precision tank gauging approach used primarily for liquids, supporting level, interface, and density measurement. It is typically selected for inventory management and loss control where accuracy and repeatability are central requirements, including applications tied to custody transfer practices. Servo gauging occupies a specialized niche: it is more mechanically involved than non-contact radar, but it can deliver excellent performance when engineered into a tank gauging architecture.

The measuring principle uses a small displacer that is positioned in the liquid by a servo motor. The displacer hangs from a measuring wire wound onto a finely grooved drum, and when it touches the liquid, buoyancy reduces its effective weight. This changes torque in a magnetic coupling, which is measured (e.g., via Hall sensors) and used to control position precisely and determine level. The method directly leverages buoyancy physics for accurate surface (and interface) tracking.

Benefits focus on precision and application fit for gauging. Servo devices are described as unaffected by medium properties such as conductivity or dielectric constant, helping maintain accuracy across varying hydrocarbon compositions. They are also explicitly positioned for custody transfer and inventory control use cases, including measurement in crude oil and refined products. In practice, servo gauging can support rigorous operational accounting and high-confidence tank farm management.

Typical applications include crude oil, gasoline, diesel, petrochemicals, and chemicals - especially in large storage tanks at terminals, refineries, and chemical sites. Servo gauging can also be used when interface and density measurements are required for quality or separation control. It is commonly integrated into broader tank gauging systems, feeding supervisory inventory platforms and reconciliation tools alongside temperature and other custody parameters.

Engineering considerations include mechanical integrity, stilling well use (when required by tank conditions), and maintenance strategy for moving components. Wire management, displacer selection, and calibration practices should align with the measurement objective (inventory vs. custody transfer) and the product’s buoyancy behavior. When deployed as part of a disciplined tank gauging program, servo measurement provides a highly accurate and durable reference for inventory and transfer-related decisions.

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