Servo Level Measurement

Servo Level Measurement

Servo level measurement is applied to continuous liquid level measurement in custody transfer and inventory control applications. A servo gauge typically uses a displacer suspended on a measuring tape/wire; a control loop maintains the displacer at the liquid surface (or interface) and infers level from the tape position with very high resolution. This positioning-based approach is associated with high-accuracy tank gauging where inventory reconciliation and transfer accountability are paramount.

The benefit is precision and stability over long operating periods. Servo gauges can provide highly repeatable level measurements and, depending on configuration, can also support interface detection and additional inferred properties tied to buoyancy behavior. In tank farms and terminals, this level of measurement fidelity supports tighter stock management, improved loss control, and confidence in transfer calculations.

As with most mechanical gauging systems, installation and operating conditions matter. Turbulence, heavy vapor condensation, or significant product agitation can affect the displacer’s behavior unless a stilling well or calm zone is provided. Mechanical components (tape, drum, seals, displacer) require periodic inspection, and the mounting arrangement must protect the measurement path from snagging, wind effects (for open roof scenarios), or interference from internals.

Typical applications include large atmospheric storage tanks in terminals, refineries, and chemical tank farms, as well as process storage where high-accuracy inventory control is required. Interface measurement is often used to track water bottoms or phase boundaries in hydrocarbon storage. Servo gauges are also applied where legacy tank gauging architectures and custody-transfer practices are standardized on mechanical reference methods.

Selection work typically addresses gauging standard requirements, stilling well design, displacer selection, and integration into the site’s tank management system. Data interfaces, redundancy strategy (often paired with radar for diversity), and calibration/verification procedures should be aligned with the facility’s measurement governance model so accuracy targets are maintained across audits and operational cycles.

George E. Booth Co., an exclusive authorized representative of sales and service for Endress+Hauser.