HART Specifications 7.9 Release and Member Webinar

FieldComm Group is excited to announce the release of HART Communication Protocol Revision 7.9.

HART 7.9 includes 6 improved specifications:
  • FSK Physical Layer Specification, Revision 9.1.1 (errata)
  • Network Management Specification, Revision 4.0
  • Command Summary Specification, Revision 11.0
  • Common Practice Command Specification, Revision 13.0
  • Common Tables Specification, Revision 27.0
  • Command Response Code Specification, Revision 7.0
The updates included in HART 7.9 do not share a common technical theme and include the following enhancements :
  1. General improvements to the protocol (e.g., Digital Write Protect)
  2. Enhancements to further simplify HART-IP (DiffServ, ZeroConf)
  3. Simplified and streamlined requirements for HART Generic Hosts
  4. Promulgation of a safety layer compatible with all HART communication technology - SafeHART™
  5. Editorial improvements, clarifications and corrections 
Below are the details of the enhancements listed above:

1. Digital Write Protect

Digital Write Protect is a set of Common Practice Commands that effectively allows a Write Protect jumper be applied to a field device via HART Communications. This allows Write Protect to be applied without physically climbing a tank/silo or opening a device in a hazardous environment.

Conceptually, Digital Write Protect is similar to industry standard Lockout-Tagout safety practices. Digital Write Protect includes two software-based combination locks. Each lock consists of "user" and a "combination" (just like a combination lock with a tag hanging from it). As in Lockout-Tagout practice, the user is the name of the individual or group owning the digital lock. The user defines (and keeps secret) the combination when attaching the lock. The user can be read by anyone so they can be located by the plant team (as needed). Writing the (secret) combination allows the digital lock to be removed and write protect disabled.

The Digital Write Protect does not dictate specific plant policies but the digital locks are very robust and their use can be aligned to fit end user needs and practices.

2. Simplifying HART-IP deployment and management

The evolution of HART-IP continues to focus on simplifying commissioning, deployment and operation. This release adds support for ZeroConf (zero configuration networking) and prioritized routing of HART-IP packets (DiffServ).

ZeroConf consists of two standard technologies: mDNS (RFC 6762) and DNS-SD (RFC 6763). mDNS and DNS-SD enable zero configuration ("ZeroConf") deployment in most networks (with or without DNS and DHCP servers).

mDNS (multicast DNS) allows devices to confirm that their HOSTNAME is unique. HART-IP specifies default IP address for devicess while mDNS allows probing of the network and self-assigning a different, unique IP address to avoid duplicate IP addresses on the network. This enables HART-IP network operation even when DHCP and DNS servers are not present.

DNS-SD (Service Discovery) enables directories of all HART-IP network devices to be constructed and presented to the user. These DNS-SD allows the HOSTNAME, Unique ID, Manufacturer, Device Type, instrument type and more to be previewed without physically opening a session to the HART-IP device. Since this allows the FDI Device Package or the DeviceInfo to be identified, additional device characteristics (e.g., a list of its process variables) could be generated and presented to the user.

DiffServ (RFC 2474) allows the Quality of Service (QoS) for HART-IP communications to be specified (using Common Practice Commands) in the HART-IP device itself.

Since 2000, DiffServ ("Differentiated Services") has allowed IP communication traffic to be classified and Quality of Service (QoS) for that traffic to be ensured. The Differentiated Services Code Point (DSCP) sets the priority for Internet communication. The DSCP setting (in the IP header) is then used by network switches on a Per Hop Basis (PHB) to ensure compliance with end-to-end QoS objectives.

For example:
  • DiffServ is widely used in banking a trading network to ensure the priority delivery of time-critical financial transactions
  • Process monitoring and control communication can be assigned a low-latency low-loss priority
  • Web page traffic (HTTPS) or security cameras can be assigned lower priority.
3. Simplified Generic Host Requirements
A Generic Host can perform basic configuration of any HART-enabled field device without needing an EDD or FDI Device Package. In some cases, a Generic Host supports more commands than found in some simple devices. Basic configuration includes:
  • Configuring HART communications (tags, Join Keys, Network ID, PreShared Keys, syslogging settings, DiffServ)
  • Setting 4-20mA Range Values, configuring unit codes, etc.
Historically, Generic Hosts have been required to support all Read and Write Common Practice and WirelessHART Commands. This has evolved over time to quite a long, onerous list. In this release, Generic Host requirements have been updated and simplified. Requirements to support esoteric and the less than useful commands were removed. Basic support for HART-IP and Discrete Device was added.

4. SafeHART™

SafeHART enables communication of digital safety data. SafeHART adds sequence numbers and CRC to standard HART packets enabling SIL-3 rated communication over HART-IP and WirelessHART. HART 4-20mA communication achieves SIL-2 with no special system level requirements. SIL-3 can be achieved using modest system design techniques (e.g., adding a redundant SIL-2 HART 4-20mA device).

SafeHART publishes safety data from the field using HART "Burst-Mode". As SafeHART is backward compatible, the safety packets traverse existing HART-enabled networks without requiring any changes to installed WirelessHART Gateways and HART 4-20mA remote I/Os. HART-IP nodes (Gateways, I/O and field devices) push published data to multiple clients, and compliant applications (e.g., monitoring and optimization) can consume the published payloads without those applications being modified either.

SafeHART enables setpoints to be digitally written using the normal HART request/response pattern. HART supports several profiles for digital control in field devices including the Modulating Final Control (FCG TS20160.15) for actuators, valves, etc. and the PID Control (FCG TS20160.7) for positioners. SafeHART is directly applicable to safely writing setpoints using these two HART standards.

5. Editorial improvements, clarifications and corrections

Per our standard practice, editorial improvements, clarifications and corrections were made as part of the general review of the specifications. For example, the errata to *FSK Physical Layer Specification* fixed a number of typos.
The collection of updated HART Protocol Specifications is available for viewing on FieldComm Group's website. The specifications can also be downloaded by FieldComm Group Members via ShareFile. If you do not have ShareFile access, please submit a support ticket.
For additional information, please visit the support portal.
Member Webinar
Please register and attend our exclusive member webinar to get the details about the HART 7.9 release. We will have a Question & Answer session where you will be able to ask questions about the release.

This webinar will provide a technical summary of the major enhancements included in the HART 7.9 release. We will also provide references to the pertinent specifications, a description of the benefits and guidance on implementation for each enhancement. 
Register for Member Webinar