Siemens PLC-based Control System

Overview

Our co-sponsors, Siemens Healthcare and the U.S. Navy, have tasked us with supporting a naval ship’s center of gravity with a control system. While fuel is moved from a holding tank to a day tank the overall weight of the tank decreases. The change in weight can cause changes to the ship’s center of gravity which has detrimental effects. To counter this water is supplied to the tank to compensate for the loss in weight maintaining a (relatively) constant balance. When refueling the reverse is true. The control system must compensate for any weight lost or gained.

Objectives

This is a hydraulic system comprised of a water tank, mixed tank and fuel tank. Both water and fuel is moved by pumps at a static flowrate (10 GPM). Depending on how the valves are aligned (which valves are open vs closed) the fluid may be added to or removed from the mixed tank. Due to the difference in density between fuel and water the fuel will always be on top in the mixed tank. Assume density of water is 8.3 lbs/gal and the fuel is Diesel with a density of 7.1 lbs/gal and no mixing occurs in the mixed tank. The valves are assumed to shut and open instantly, and hydraulic resistance is not required as the flowrate will always be the same out of the pump when turned on.
• Created a simulation that accurately represents fuel tank conditions on a navy ship
• Created a simulation model to optimize fuel to water weight ratios using Siemens PLC software with custom input/output logic
• Programmed a way to alternate the precent fill of the side fuel tank from 25% to 75% while maintaining a constant weight of around 13,000 pounds in the middle tank
• The weight and volume of the middle and side tanks were calculated from using level sensors in tandem with the geometry of the tanks and the density of the fluids

Approach

• Studied sponsor provided materials on the desired schematic and system.
• Acquired laptops from sponsors with siemens software suites downloaded and licensed.
• Researched resources and completed training modules to gain proficiency and experience with Siemens PLC software.
• Developed equations and level relationships based on tank volumes and fluid characteristics.
• Met with Navy team to discuss and attain a concept of operations for tank system.
• Separated into two teams to develop the PLC code and create the simulation environment simultaneously.
• Combined and simulated the PLC code and plant environment on Siemens provided laptops.

Outcomes

The implemented control system ensures a consistent weight balance in the fuel tank system, thereby stabilizing the ship’s center of gravity during fuel transfer. This reduces the risk of sudden and unexpected negative effects caused by shifts in the center of gravity.
The optimized system reduces errors, saving the sponsors costs from maintenance and operational disruptions. The developed simulation and Siemens PLC-based model optimize the fuel-to-water weight ratio, enabling precise control and efficient operation of the hydraulic system.
A tailored input/output logic program in Siemens PLC software allows seamless alternation between 25% to 75% fill levels while maintaining the tank’s constant weight of around 13,000 pounds. This innovation provides a new, efficient method for fuel system management. Accurate Measurement and Control: Using level sensors and tank geometry, the system calculates the weight and volume of tanks with high precision. This enhances decision-making during operation and reduces manual monitoring requirements. Scalable Simulation Models: The project resulted in a scalable simulation tool that the sponsors can use for future ships or related hydraulic systems, paving the way for widespread application across naval vessels.