A duct flow sensor is a device used to measure the rate of air flow in a duct system. It is typically used in HVAC systems to measure the amount of air being delivered to a space. The sensor works by measuring the pressure difference between two points in the duct system. This pressure difference is then used to calculate the rate of air flow. The sensor can be used to measure the flow of air in both supply and return ducts. It is important to note that the accuracy of the sensor is dependent on the type of duct system being used and the size of the ducts. The sensor is also used to monitor the efficiency of the HVAC system, as it can detect any changes in air flow that may indicate a problem.