In diagnosing chattering, which action is appropriate?

• A. Inspect for actuator saturation
• B. Replace the sensor
• C. Increase the setpoint
• D. Ignore discretization effects

Answer: (A)

Chattering happens when the control action causes rapid on-off-like behavior, often because the actuator can’t move beyond its limit. The most direct way to diagnose this is to inspect for actuator saturation. If the actuator is hitting its maximum or minimum and the controller keeps trying to correct, the output spends time pressed against the limit and then releases, producing quick, back-and-forth oscillations in the process variable.

To check this, look at the controller output signal and the actuator’s actual position or valve opening. If you see the command sat at a limit while the process variable still oscillates, saturation is the likely cause. You can confirm by temporarily reducing the controller gain or adding anti-windup/rate limits and observing whether the chattering diminishes.

Replacing the sensor doesn’t directly address chattering caused by actuator limits, increasing the setpoint would typically push the system closer to saturation and worsen the issue, and ignoring discretization effects may miss digital sampling problems that could contribute in some cases but isn’t the primary fix here.