In BACnet, what is the difference between an AI object and an AO object?

• A. AI is Analog Input and AO is Analog Output
• B. AI is Analog Output and AO is Analog Input
• C. AI and AO are both digital
• D. AI is Alarm Input and AO is Alarm Output

Answer: (A)

This question tests how BACnet distinguishes two common analog points: sensor inputs versus actuator outputs. An Analog Input (AI) object represents a sensor reading from the environment—the value you read from a device like a temperature sensor. An Analog Output (AO) object represents a control signal sent to an actuator—the value you write to drive something, such as a valve position or motor speed.

So the key idea is the direction and purpose of the point: AI is the input the system observes, AO is the output the system commands. Both are analog, not digital, and they describe different roles in the control loop.