Control Modes Fundamentals: ON/OFF Control
📌 ON/OFF control, also known as Two-position control, changes the controller output between two fixed conditions (ON or OFF).
💧 The controller output is ON when the Process Variable (PV) is below the Set Point (SP), and switches OFF when the PV exceeds the SP.
📈 This results in the Process Variable fluctuating cyclically around the set point due to a differential gap in the control action.
🏡 Applications suitable for this mode include systems where fluctuation is acceptable, such as liquid level control, home heating systems, and domestic water heaters.

Control Mechanism Example
⚙️ Initially, with the liquid level (PV) below the desired SP, the controller is ON, opening the valve to increase the level.
🛑 Once the level reaches the SP, the controller switches OFF, closing the valve, causing the level to gradually decrease based on consumption.
🔁 The cycle repeats: when PV drops below SP, the controller switches back ON to open the valve maximally.

Upcoming Topics
➡️ The next control mode to be discussed is Proportional Control (P), defined by a constant relationship between its input and output.

Key Points & Insights
➡️ The fundamental definition of a control mode relies on the error (difference between PV and SP) to determine the controller's output.
➡️ ON/OFF control is appropriate for large capacity systems where minor, cyclic variations around the set point are tolerable.
➡️ Understanding the differential gap is crucial, as it dictates the boundaries for switching the controller output between its two fixed states.

📸 Video summarized with SummaryTube.com on Dec 09, 2025, 21:28 UTC