Question

What type of controller is commonly used to regulate temperature in a bioreactor?

• A. PID controller
• B. ON/OFF controller
• C. Bang-bang controller
• D. Proportional controller

Hint:

• ON/OFF (Bang-Bang) Controller Simple, but causes oscillations.
• Proportional (P) Controller Reduces error, but may have steady-state offset.
• Proportional-Integral (PI) Controller Eliminates steady-state error, but can slow response or increase overshoot.
• Proportional-Integral-Derivative (PID) Controller Combines benefits of P, I, and D actions for good stability, accuracy (no offset), and transient response. Widely used for process control.

Answer 1

The Correct Option is A

Regulating temperature accurately and stably is crucial in most bioreactor operations.

• (b) ON/OFF controller (or Bang-bang controller - option c): This is the simplest type of controller. It switches the heating or cooling element fully ON when the temperature deviates beyond a setpoint by a certain amount, and fully OFF when it returns within a range. This can lead to oscillations (overshoot and undershoot) around the setpoint and may not provide very precise temperature control.
• (d) Proportional (P) controller: The controller output is proportional to the error (difference between setpoint and measured temperature). It reduces oscillations compared to ON/OFF but can result in a steady-state error (offset).
• (a) PID controller (Proportional-Integral-Derivative): This is a widely used and effective feedback controller that combines three control actions:
  • Proportional (P): Responds to the current error.
  • Integral (I): Accumulates past errors to eliminate steady-state error (offset).
  • Derivative (D): Responds to the rate of change of error, anticipating future error and improving stability and transient response (reducing overshoot).
  PID controllers provide robust and precise control for many processes, including temperature regulation in bioreactors, where maintaining a stable and accurate temperature is often critical for optimal cell growth and product formation.

While simpler controllers like ON/OFF or P might be used in some less critical applications, for precise and stable temperature control in bioreactors, PID controllers are very commonly employed due to their ability to handle disturbances, eliminate steady-state error, and provide good transient response. \[ \boxed{\text{PID controller}} \]