In automatic boiler controls, which two inputs are used for the minimum signal selector?

The correct choice is based on the operational principles of automatic boiler controls, specifically regarding the functionality of the minimum signal selector. In automatic boiler systems, the minimum signal selector is designed to ensure that the boiler operates efficiently and can respond to the lowest demand requirements accurately.

The primary input signals that the minimum signal selector uses are master demand and airflow. Master demand reflects the overall heating demand required from the system, whereas airflow is crucial because it dictates how much air is available for combustion. By using both of these inputs, the system can optimize its performance, ensuring that the boiler provides enough heat to meet the demand without wasting fuel or generating excess emissions.

These inputs are essential in maintaining the balance and efficiency of the boiler's operation, as they directly affect combustion efficiency and system responses to varying heat demands. Hence, the combination of master demand and airflow is critical for the effective functioning of automatic boiler controls, making this choice the right answer.