The HD67909-A1 are Modbus TCP / HART converters.
They allow to monitor HART devices (like Sensors, etc..) with a Modbus TCP net (like PLC, Supervisory System etc..).
On the HART side, the HD67909-A1 can manage up to 15 deivces (+1 Secondary Master).
HD67909-A1 supports HART FSK.
HD67909-A1 can be used like Primary HART Master or like Secondary HART Master
For informations about Modbus / HART converters