The QTR. series air quality transmitter is an instrument that can measure various physical quantities in the air, such as temperature, humidity or carbon dioxide (CO2) and other physical parameters. It is suitable for air quality monitoring in indoor places, such as residences, factories or office buildings. It is made of sophisticated semiconductor chip sensing elements combined with integrated circuits, which can convert the measured physical values into RS485 digital output signals or voltage/current analog output signals for users to grasp the environmental conditions in real time. It can also be combined with a dedicated controller or a programmable controller to form an automatic control system to maintain healthy indoor air quality and effectively save energy.