The Honeywell C7660A1000 Dry Bulb Temperature Sensor is used for return air measurement in HVAC systems. This sensor effectively provides the air temperature and sends a proportional 4-20mA analog signal to a controller. It is with this information that the controller then has to turn up the heat or cool it as the case may be. This sensor is widely applied in building automation syste... https://www.partshnc.com/drybulbtempsensreturnair4-20ma-2