A servo tank gauge (STG) is a high-precision instrument used to measure the liquid level, interface level, and density in storage tanks, particularly in industries like oil & gas, petrochemicals, and chemicals.
What Is a Servo Tank Gauge?
A servo tank gauge is a non-contact level measurement device that uses a servo motor mechanism to control the position of a sensing element (often a displacer or a float) suspended by a wire inside a tank. It provides real-time, high-accuracy readings of:
Liquid level
Interface between two immiscible liquids (e.g., oil and water)
Liquid density
Temperature (when integrated with a multi-spot thermometer)
How It Works:
A small displacer is suspended into the tank by a wire or tape connected to a servo motor in the gauge head.
The servo motor maintains the displacer at neutral buoyancy (constant tension).
By measuring the amount of motor torque or movement required to hold the displacer in place, the system can determine:
Liquid level (based on immersion depth)
Density (based on buoyant force)
Interface level (if there’s more than one liquid)
✅ Key Advantages:
Very high accuracy (±0.4 mm or better in modern systems)
Multi-variable measurement (level, interface, density)
Suitable for custody transfer and inventory management
Compatible with tank gauging systems (e.g., Rosemount, Honeywell Enraf, etc.)
Non-intrusive versions available for certain applications
Typical Applications:
Oil terminals and depots
Refineries
Chemical plants
Liquefied gas storage (LPG, LNG)
Custody transfer stations