Servo Level Measurement

Servo Level Measurement

Servo level measurement (servo tank gauging) is a high-precision method for measuring liquid level, interface, and density, often associated with custody transfer and inventory control. It uses a displacer and servo mechanism to track the liquid surface with exceptional resolution. The technique is typically applied where small measurement errors translate into significant commercial or operational impact.

The measuring principle positions a small displacer in the liquid using a servo motor and a measuring wire wound on a precision drum. As the displacer contacts the liquid, buoyancy reduces its effective weight; the resulting torque change in the coupling is detected and used to maintain the displacer at a defined equilibrium point. The instrument’s controlled position corresponds to level, and additional evaluation can support interface and density measurements.

Benefits focus on accuracy and repeatability across a wide range of liquid properties, including reduced sensitivity to conductivity and dielectric variations. Servo gauging is strongly associated with inventory management and loss control and is commonly aligned with recognized standards and approvals used in regulated transfer applications. When properly installed, it supports reliable tank accountability and high-confidence measurement for valuable products.

Typical applications include crude oil, refined products (gasoline, diesel), and petrochemical or chemical storage where custody transfer or high-integrity inventory control is required. It is also used for interface detection in tanks where water bottoms must be tracked with precision, and in applications where density profiling supports product quality or reconciliation.

Selection and integration should consider tank geometry, stilling well requirements (where used), expected surface turbulence, and product contaminants that could foul moving components. Because the method includes mechanical motion, maintenance strategy and access should be planned. Signal integration with tank gauging systems, temperature/pressure compensation schemes, and calibration workflows should be defined to match the site’s custody transfer and reconciliation practices.

Forberg Smith, an exclusive authorized representative of sales and service for Endress+Hauser.