Developing a Distributed Control System for Educational Training Based on NI FieldPoint and Lookout

Author(s):
Sorin Carari - Technical University of Iasi
Corneliu Lazar - Technical University of Iasi
Ovidiu Chirea - Technical University of Iasi

Industry:
University/Education

Products:
Compact FieldPoint, Lookout, FieldPoint,

The Challenge:
Implementing a flexible, reconfigurable control system for educational purposes and research that implements control structures with PID controllers such as cascade control and ratio control for a Feedback PROCON Level/Flow and Temperature Process Rig.

The Solution:
Developing a control solution using FieldPoint distributed I/O modules and Lookout graphical development environment to monitor, record, and control the process parameters.

Applying Automatic Control Strategies
The modern industrial systems tend to replace traditional point-to-point communication architecture with common bus network architecture to connect sensors, actuators, and controllers. In accordance with this new trend, we at the Technical University of Iasi have improved our process control laboratory infrastructure with software and hardware equipment used in distributed process control systems. In the frame of the process control laboratory, the students can apply the automatic control strategies presented on syllabus on industrial equipments.

A few essential keys in the educational training using experiments are the flexibility in choosing the tuning parameters of the control law and the possibility to monitor and record the process variables. In accordance with these requirements, we developed a flexible and easily reconfigurable distributed control system using NI Lookout software and FieldPoint I/O modules.

As a study process, we used a feedback process rig. With this laboratory setup, we can control temperature, flow, and/or level. Also, we can configure the system to illustrate very complex control structures, such as cascade or ratio control.

Advantages of Using PID Controllers
The Lookout software application implements the control of flow and level, cascade, and direct and indirect ratio control using PID controllers.

The main panel contains a schematic description of the controlled process with information about sensors status and a set of buttons for choosing the control structure. When we choose the desired control structure, the system displays a new window with the status of the PID controller and process outputs. There the tuning parameters and the reference and/or the automatic or manual control mode can settle. The PID controllers have the same functionality as the industrial one, but with a friendlier user interface. Thus, the students can make more practices for a better understanding of tuning parameters influence instead of navigating through a complicated menu structure.


Using the buttons labeled MONITOR and PID OUTPUT, the system displays the windows that contain the time plots of monitored process variables. In the MONITOR window, the system plots the references and process outputs. In the PID OUTPUT window, the system plots the controller output. The monitor windows offer the facility to display just a part or all of signals or to freeze the monitor to appreciate the obtained performances. Also, we can modify the time range of graphics using a slider button. The monitored variables are automatically recorded into a database for later visualizations.

We illustrated cascade control by choosing the primary process output as the level, and the secondary variable as the water flow. Such a control structure can greatly diminish the effect of water supply pressure variations on the level. The implemented cascade structure permits to present the purpose and theory of cascade control and to explain the method of tuning cascade controllers.

For ratio control, we used two flows proportional to each other. We implemented direct and indirect schemes to compare the performances of these two ratio control structures and to decide which schemes we prefer.

To connect the PC to the process rig, we used one bank of FieldPoint modules, which consists of an FP-TB-10 terminal base module equipped with analog input and output current modules and an Ethernet communication module. These modules are wired to the process interfaces and connect to the transducers and actuators from the plant. Because of the small size of the FieldPoint modules, we could mount them at an optimal distance from the plant, reducing the wire lengths. The reduced length of wires has a good impact not only in costs, but also in the quality of the acquired signals, which are less affected by noise. Using the Ethernet to transfer data from I/O modules to the PC eliminated the electrical noise interference with analog signals and ensured data integrity.

Because of the complexity of the application, we could not have developed it in the short few months that we did with any other software package than NI Lookout. Its programming facilities prove ideal for educational training applications.

The future developments of the system include the autotuning function for PID controllers, ON/OFF temperature control, and Web accessibility. We believe that we can easily accomplish these tasks because of the open architecture of Lookout.

System benefits include:

• Simplified switching between control structures with just few mouse clicks, and is not required to shut down the laboratory plant
• Continuous real-time access to all monitored variables
• Highly reduced application development time
• Reduced wiring and space necessities
• Facilities for implementing more complex structures such as cascade and ratio control
• Easy future developments

Ability to Perform a Variety of Experiments
Using Lookout software and FieldPoint hardware, we have obtained a flexible, reliable, user-friendly, and cost-effective distributed control system. Now the students can perform a wide variety of experiments to improve them knowledge in process control engineering. This procedure introduces the students in the research and developments activities for process control.

For more information, contact:
Sorin Carari
Technical University of Iasi
Department of Automatic Control and Industrial Informatics -- Romania
Tel: +40-232-230751
E-Mail: scarari@ac.tuiasi.ro

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