Objectives and descriptions of PID-related labs at Missouri University of Science and Technology

In our January 2017 edition of Control Talk, Greg McMillan and Stan Weiner speak with Dr. Kelvin Erickson of Missouri University of Science and Technology, regarding his approach to preparing students for the future of process control. Below, learn more about some of the PID-related labs offered. 

Heat and ventilation control

Objective - This exercise is designed to provide a start-up sequential operation and continuous operation with a PID controller in a pressure and temperature control application. Also, regulatory control is demonstrated by alternating the setpoint to the PID controller. A simple HMI display is also part of the exercise.

The students program a PLC to start up the process by testing that the pressure sensor and fan drive are working by running the fan at 50% speed and waiting for the duct pressure to reach 0.1 inches of water. Then the temperature sensor and heater are tested by running the fan at 25% with the heater coil on waiting for the temperature to rise 1 degree C. After passing the two tests, normal operation is activated that controls the pressure and temperature to the high setpoints for 30 seconds and then controls the pressure and temperature to the low setpoints for 30 seconds. This operation continues until the system is reset. If the pressure test or the temperature test takes more than 60 seconds, then the system stops and alerts the operator.

pH Control

Objective - This exercise is designed to provide a start-up sequential operation and continuous operation with a PID controller in a pH control application.

The students program a PLC to start up the process by allowing the unknown stream to start filling the empty tank. When the pH probe is immersed, the pH PID controller is activated and then it controls the valves for the acid and base inlet streams to control the pH of the tank contents to be within the range of 6.5 to 7.5. When the tank level is 10 cm and the pH is within the acceptable range, the level PID controller is activated to control the outlet valve position to maintain the tank level at 10 cm. If the pH is not in the acceptable range when the tank level initially reaches 10 cm, then the tank is "spiked" with acid or base for a few seconds in an attempt to bring the pH into control. When the pH comes within the acceptable range, then the level PID controller is activated to maintain the tank level at 10 cm. If the pH is not within the acceptable range when the tank level reaches 15 cm, then the tank is drained to 5 cm and the operation is restarted.

Heat Exchanger Control

Objective - This exercise is designed to provide a simple PID control for a heat exchanger application. Also, regulatory control is demonstrated by alternating the setpoint to the PID controller. A simple HMI display is also part of the exercise.

The students program a PLC to start up the process by turning on the tank immersion heater and pump with the regulating valve at 25% and wait for the hot water temperature in the hot water loop to rise 3 degrees or attain 30 degrees C, whichever is first. Then the students adjust the cool water flow to 2000 ml/min. After reaching this flow, the temperature PID controller is activated to control the temperature of the cool water loop by adjusting the regulating valve position.

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