To complete the sequence of operation in an HVAC Control System, there are additional components required to confirm operations in the system.
Temperature Sensors are useful in sensing the temperature differences across coils, mixed air conditions, etc.
Amperage Sensors can sense when compressors, fans etc. are operating.
Air Flow Sensors can sense the differential pressure and be used to sense airflow, and differential pressure across air filters to alarm when they should be changed.
Pressure Transducers allow for a modulated signal on the differential pressure and can be connected to display duct pressures in real time, showing pressure differential across Filters, Rooms, and be set up with a flow station to read airflow.