Extrapolating to a more general basis for industrial plant applications, the bandwidth consumption by a large WirelessHART network will be no more than 10% of the available bandwidth in the 2.4 GHz band in any industrial plant.
A WirelessHART network with any conceivable number of devices cannot consume all of the 2.4 GHz bandwidth in any installation.(For a bandwidth usage calculator for WirelessHART networks, see HART 7: Installing and Making Systems Work in this issue.)
Coexistence with other networks
Coexistence is the ability of one system to perform a task in a given shared environment in which other systems perform their tasks and may or may not be using the same set of rules. This is the IEEEs definition of coexistence and serves to illustrate the difficulties faced by the HART 7 design team when they faced the creation of a wireless version of HART.
There are a very large number of wireless networks and devices that WirelessHART must coexist with, including cordless telephones, microwave ovens, WiFi, WiMAX and other wireless sensor networks, such as Zigbee and Bluetooth.
WirelessHART is designed using standardized IEEE radios, clear-channel assessment, blacklisting, channel-hopping, mesh-to-the-edge networks, and redundant path routing, to coexist with any other network in the 2.4 GHz band, and not only to not interfere with other networks, but also to not allow other networks to interfere with WirelessHART.
Interfacing with control systems
A WirelessHART gateway is a remote I/O system for connecting WirelessHART devices to plant control and/or asset mangaement systems (new or existing). Since WirelessHART is backward compatible with wired HART, the WirelessHART gateway allows integration to plant systems in the same way I/O systems do for traditional wired HART devices. Like existing remote I/O, gateways will offer a variety of host-side interfaces to standard industrial communication networks like Modbus, Profibus, Profinet, Foundation Fieldbus, OPC XML, RS-485, Ethernet, and others.
Every major asset management software vendor produces HART-enabled products that will interface directly with the digital data provided by the WirelessHART gateway. So all users have to do is connect either a native WirelessHART product or a WirelessHART adapter to an existing HART-enabled device, achieve communications at the gateway, and connect the gateway to their existing HART-enabled software, whether it is a control, asset-management, or CMMS system. This releases the stranded HART diagnostic information and makes it possible to implement state-of-the-art predictive maintenance where it was not cost-effective before.
Industrial control systems have traditionally been built with little regard for security. Denial-of-
service attacks, spoofing of identities, authentication issues, industrial espionage, and terrorist attacks, along with invasion by organized crime and damage caused by disgruntled employees are among the threats faced by all control systems.
HART 7 permits a single system of secure communications. Critical measurements should be wired using HART-enabled instruments. Less critical measurements and control parameters can be wireless. But all HART 7 communications are secure.
WirelessHART is secure. The data is encrypted with 128-bit AES encryption, a strong cipher. Provisioning (hooking up a new device to the network) is accomplished by secure join keys which are entered into the device via a secure wired connection. All messages are encrypted and individual session keys ensure that only valid devices can pass information in the network. End-to-end data encryption is employed to prevent sensitive data from being intercepted. Message Integrity Codes (MICs) are generated after the data is encrypted to sign the data end-to-end. Denial-of-service attacks are mitigated with channel-hopping and redundant paths provided by the mesh infrastructure. Password protection (secure keys), white lists, and black lists prevent unauthorized devices from joining the network and communicating on the network. The use of individual encryption codes and passwords on a point-to-point basis provides secure authentication for WirelessHART.
Registration program for devices
Like all HART devices, all WirelessHART devices must undergo detailed testing before receiving the right to display the HART Registered mark.
Interoperability between different device suppliers is tested and guaranteed through this testing program. Using HART Communication Foundation standard testing tools, such as the Wi-analys device pictured on the left, suppliers test their device to confirm compliance and submit a Device and Test Report to the Foundation.
The HCF audits the Test Report and conducts an independent test to verify compliance to the standard. This is the only way for a supplier to obtain a HART Registered Certificate and only HCF-registered devices can claim to be WirelessHART-compliant.
WirelessHART security diagnostics
WirelessHART devices have all the same universal set of diagnostics as wired HART devices, plus additional standardized diagnostics specific to the wireless connection. Among the diagnostics available to all WirelessHART devices are
- Device malfunctionSimply stated, the number one alarm to monitor (check device immediately)
- Configuration changeSystem verification of configuration changes (confirm device reconfiguration was correct)
- Cold start or resetPower supply problems (monitor for continued problems and repair as needed)
- More status availableMore information exists to troubleshoot device (a DD-enabled host application can retrieve additional device specific diagnostics)
- Loop Current fixedThe analog output should not be used for control (may or may not be an error)
- Loop Current saturatedThe analog range has been exceeded (the digital value should be used for the measurement)
- Non PV out of limitsVaries by device type: for example, a multivariable device with a temperature measurement may have exceeded operating range (verify device accuracy)
- PV out of limitsDevice measurement range has been exceeded (verify device accuracy)
- Maintenance Required
- Device Variable Alert
- Low Battery
- Critical Power Failure
All devices build and maintain a list of neighbors. All devices report their neighbor list and network health. Some of the network health parameters include average latency measurement per device, path down alarms, number of lost packets (should be zero), and devices-per-access-point loading.
The WirelessHART specifications were built on proven industry standards with support from nearly all major vendors of automation systems and devices. The HART Protocol continues to be enhanced to meet the changing needs of the process industry and to adapt to new instrumentation technology, such as wireless. The backward-
compatibility of HART Protocol revisions ensures that an investment made in a HART device or system is protected into the future.
The wide adoption of WirelessHART by automation product manufacturers ensures that WirelessHART devices have the same security as investments that HART devices have proven to have for over 18 years.