🔍 Key Concepts

• Proportional vs integral vs derivative vs on‑off control – how each one changes the output when the process variable moves away from the setpoint • How a float level controller works when it is mechanically linked to a control valve or pilot piston • Whether the control element in the sketch moves in small continuous steps or jumps between two extreme positions

💭 Think About

• Look at the float, linkage, and pilot/master piston. As the liquid level moves slightly up or down from the set point, does the valve position change gradually with the size of that movement, or only when a limit is reached? • Ask yourself if this system seems to respond to (a) the size of the error right now, (b) how long the error has existed (accumulated error), or (c) how fast the level is changing. • Consider whether this controller can hold an intermediate valve position, or if it appears designed to snap fully open or fully closed when the level crosses the setpoint.

✅ Before You Answer

• Identify the process variable (what is being measured) and the final control element (what is being moved). • Decide if the controller output is continuous and proportional to error, based on accumulated error over time, based on rate of change, or only two‑position (open/closed). • Verify how the turnbuckle set point adjustment would affect the controller’s action and whether that matches one specific control mode.