Which of the following statements is true about using PID instructions?

The statement that PID instructions can respond to changes in setpoints and process variables is accurate. PID control, which stands for Proportional, Integral, and Derivative control, is designed to continuously adjust the control output based on the difference between the desired setpoint and the actual process variable. This means that when the setpoint changes or when there are fluctuations in the measured process variable, the PID controller can adapt its output to maintain the desired process condition. This adaptability is one of the main benefits of using a PID controller, as it helps maintain stability and performance in various control systems.

Other options present limitations or inaccuracies regarding the capabilities of PID control. For instance, claiming that they only allow proportional control functions overlooks the integral and derivative components that enhance PID control's responsiveness and accuracy. Suggesting that they can replace all forms of control strategies dismisses the value of other control methodologies that may be more suited for specific applications. Finally, stating that they require external sensor inputs only implies a restrictive viewpoint, whereas PID controllers can also utilize internal variables or signals depending on the control architecture.