The Components of WirelessHART technology
A Gateway provides the connection to the host network. WirelessHART and then the main host interfaces such as Modbus – Profibus – Ethernet. The Gateway also provides the network manager and security manager (these functions can also exist at the host level – however initially they will be in the gateway)
The Network manager builds and maintains the MESH network. It identifies the best paths and manages distribution of slot time access (WirelessHART divides each second into 10msec slots) Slot access depends upon the required process value refresh rate and other access (alarm reporting – configuration changes)
The Security manager manages and distributes security encryption keys. It also holds the list of authorized devices to join the network.
The Process includes measuring devices – the HART-enabled instrumentation.
A Repeater is a device which routes WirelessHART messages but may have no process connection of its own. Its main use would be to extend the range of a WirelessHART network or help “go around” an existing or new obstacle (New process vessel). All instruments in a WirelessHART network have routing capability which simplifies planning and implementation of a wireless network.
The Adapter is a device which plugs into an existing HART-enabled instrument to pass the instrument data through a WirelessHART network to the host. The adapter could be located anywhere along the instrument 4-20mA cable; it could be battery powered or obtain its power from the 4-20Ma cable. Some adapters will be battery powered and use the same battery to power the instrument as well – in this case there will be no 4-20mA signal to the host – all process data will be reported via WirelessHART
A Handheld Terminal may come in two versions. In the first case, the handheld will be a standard HART FSK configuration unit (just add new device DDs or DOF files), just like the one used for everyday tasks such as routine maintenance and calibration checks. In the case of wireless support, the handheld is used to join a new instrument to an existing WirelessHART network.
In the second case the handheld has a WirelessHART connection to the gateway and then down to an instrument and could be used for reading PV or diagnostics.