What is a Servo gauge?
Servo gauge system is used to measure the liquid level in large storage tanks. There are many tools and systems available that can provide a mix of measurements that will enable precise quantity evaluation and, therefore, excellent inventory management. In practice, for tank gauges, we use both radar and servo level transmitters
Construction of Servo gauge system?
Using a servo motor, a tiny displacer is placed precisely in the liquid medium. The displacer is suspended on a measuring wire wound inside the tool onto a fine grooved drum housing.
The drum is driven by coupling magnets, separated entirely by the drum housing. The external magnets are connected to the wire drum while the internal magnets are connected to the motor drive.
As the magnets turn, the magnetic attraction also turns the outer magnets, resulting in the complete drum assembly being turned over. The displacer’s weight on the wire creates a torque on the outer magnets that generates magnetic flux change.
How does the servo gauge works:
The servo gauge system uses the small displacer. The displacer has buoyancy, but on the liquid it does not float. The displacer must be held on top of the tank by a thin wire linked to the servo gauge.
A servo weighing system senses the tension in the wire, signals from the weighing mechanism control an electrical motor in the servo unit and the displacer follows the liquid level movements.
An electronic transmitter sends the field bus level data to the control room reader. A still pipe is needed wherever a servo gauge is installed to prevent the displacer from drifting in the tank. In fixed roof tanks, this is also required.
Advantages of Servo gauges:
The servo gauge generally performs better than a float gauge
A freshly calibrated servo gauge can fulfill precision criteria for custody transfer.
The servo can be used to measure liquid density and water bottom levels
By measuring the tension of the wire, the liquid density can be measured at different concentrations in the tank.