🔍 Key Concepts

• Offset in control systems usually means a steady-state error between the desired value (setpoint) and the actual controlled variable • Differences between on/off (two-position), proportional, reset (integral), and rate (derivative) control actions • Which control modes do and do not eliminate steady-state error without manual readjustment

💭 Think About

• Think about which control mode naturally leaves a non‑zero difference between setpoint and actual value when the system is in steady state • Ask yourself: in which mode does the controller output depend directly on how far away the process is from setpoint, and can that alone still leave a permanent error? • Consider which mode is specifically added to remove any remaining offset after the proportional action has done its job

✅ Before You Answer

• Be clear on the definition of offset / steady‑state error in a control loop • Identify which of the listed modes can, by itself, drive the steady‑state error to exactly zero without operator intervention • Eliminate any mode whose purpose is explicitly to remove offset rather than to cause it as an inherent characteristic