WHA-GW-*
Product Specifications
221981 2011-07
13
In the next step, the network manager sends scheduling information to the field device. The
field device is told how to participate in the network and receives various information from
the WirelessHART Gateway:
• Number and identity of neighboring WirelessHART field devices,
• When to send messages and which channels to use,
• When to repeat messages for other WirelessHART field devices,
• The optimal communication path for messages as well as alternative communication
paths in case of failure.
During this process, the field device may also apply to send messages in certain intervals
and ask the network manager for the appropriate resources. The network manager then
takes care that these resources are available. For example, the network manager informs
other WirelessHART field devices when to repeat messages.
2.2.2 Security Management
The security manager is part of the WirelessHART Gateway. To make communication safe,
all messages are encrypted with industry-standard AES-128 block ciphers with symmetric
keys. Therefore, messages are unreadable for external listeners.
The security manager distributes the encryption keys and changes them in certain
(random) intervals, as an option.
2.2.3 Virtual Remote I/O system
The WirelessHART Gateway make wireless communication accessible to HOST systems
capable of HART technology through the following principles.
Instrument List
WirelessHART devices and wired devices connected to a WirelessHART adapter are made
available to HOST systems via a virtual HART I/O system. This I/O system contains one or
multiple I/O cards. Each I/O card has up to 2 channels. To each channel, up to 6 wired field
devices may be connected in multi-drop mode. (see Figure 2.3 on page 14).
The P+F WirelessHART Gateway assigns a virtual I/O card to each WirelessHART device
and stores card and channel values in the Instrument List. The I/O cards are assigned to
the WirelessHART devices in chronological order (0 ... 249). New WirelessHART devices in
the network are assigned to the next available I/O card.
WirelessHART devices are always assigned to Channel 0 of an I/O card. All wired devices
connected to a WirelessHART adapter are always assigned to channel 1 of the same I/O
card as the adapter (multi-drop mode).
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