🔍 Key Concepts

• Proportional band (PB) and how it relates to controller sensitivity or gain • Difference between proportional control and ON-OFF control in terms of how much error is needed to change output • What happens to controller action as PB approaches zero

💭 Think About

• Think about whether a wide proportional band makes the controller more like a smooth proportional controller or more like a simple ON-OFF switch • Consider what a very small proportional band means for how quickly the output jumps from minimum to maximum when the process variable changes slightly • Which option represents a band so narrow that the controller output is almost either fully on or fully off?

✅ Before You Answer

• Verify that proportional band is inversely related to controller gain (high gain = small PB) • Check which answer choices represent a very small positive proportional band, and eliminate any physically unrealistic values • Ask: which PB value would cause the controller to act almost like a switch, with output nearly full on or full off for tiny deviations?