HART Protocol Enhancements Provide Powerful New Features
The latest HART Protocol Specifications may include WirelessHART communication, but its new enhancements also enable many more capabilities for communication with intelligent field devices. There are significant additional differences and improvements between the most commonly installed and used versions of HART technology and the newest version.
Powerful New Features
The first versions of HART were designed to bring smart field devices into the world of control and automation, and they succeeded wildly. Even today, many HART devices are operated in strictly analog mode with HART used for setup and calibration. Yet the push toward added value from intelligent field devices has led to the use of HART devices in many control systems for enhanced system integration — taking the digital signal through HART multiplexers directly into the control system, for additional process variables, online diagnostics and better alarm management.
The latest version of the HART Protocol integrates wired and wireless devices into a common control network and adds additional functionality to improve alarm management and maintenance diagnosis.
“The unsolicited messaging capability is probably one of the most immediate benefits,” says Scott Saunders, vice president of sales and marketing for Moore Industries-International. “All plants are doing more with fewer personnel. Having HART slave devices that are able to perform predictive maintenance on their own is a real plus.”
New capabilities for increased intelligence and communication throughput efficiency include new features such as enhanced data publishing for process variables, configuration change and device diagnostic status alerts, with support for Report by Exception and Automatic Event Notification.
Faster configuration uploads are now possible with multiple read commands in one transaction. Plus, HART now adds a number of additional standardized device diagnostic and status parameters such as “device memory,” “power,” and maintenance and environmental variables.
Interoperability Equals Choice
The most important feature of the recent HART enhancements is the integration versatility of the technology. Wired or wireless, HART offers unparalleled ease in integration with systems. Using EDDL, OPC, and XML, HART communicates with any advanced control, simulation, asset management or enterprise integration system.
All major control system suppliers offer HART-enabled I/O as standard equipment. Almost all major field device manufacturers offer HART-enabled devices. A significant number of third-party products support integration with legacy control systems using a variety of devices such as Multiplexers (HART to RS-485) and Gateways (HART to Ethernet, HART to Modbus, HART to Profibus, etc.) and Single-Loop Monitors (devices that convert digital values and alerts to analog signals and contact closures that older DCS and SCADA systems can use) — and of course, there’s wireless.
HART Technology continues to protect the globally installed base of an estimated 30 million HART devices and supports the entire range of HART-enabled measurement, control and automation systems products, both wired and wireless. It enhances HART functionality and preserves the viability of the technology’s future indefinitely.
Key Technical Features
Longer Device Tags: Supports device tags (measurement tags) as long as 32 characters expanded from the current limitation of eight. These tags typically follow a plant or company’s defined rules, and can be quite long. HART now supports up to 32 ISO Latin 1 and international characters enables you to see the entire unique tag of the device in the asset management system.
More Dynamic Device Variables: Increases the number of mapped dynamic device variables to eight from previous limit of four. These additional measurements, calculations, or constants add depth of device or process information. It also adds the option of quality information (device status) on each variable.
Local Interface Lock: Blocks write access so set device parameters can’t be changed by an unauthorized person, accident, or conflicting tools at the same time.
Device Identification by Host: Ensures synchronization of configurations between the host and a device, so old configuration settings cannot be inadvertently used in a device. The host configuration counter verifies a device by its tag and synchronizes with it using bidirectional checking. The device configuration is checked against the system database, and can be automatically documented.
Visual Device Identification: Devices that are hidden below machinery or have unreadable tags can be ordered by the host to emit a visual or audible signal. This eases visual identification for inspection, field work, or commissioning, especially useful in multi-drop applications.
Report by Exception: Reduces data overload by restricting publishing of dynamic variable data. Data can be published in bursts, according to specific time, process window, threshold, or value criteria. No polling by the host is required.
Time-Stamped Data: Device process variables, diagnostics status, and configuration change events are time stamped. Eases sequence-of-events recording, data stability analysis (jitter), and input/output analysis.
Time-stamping facilitates more accurate process efficiency calculations and the use of digital values for control, which supports broader use of multivariable device capabilities in control systems and permits users to employ better forensics in the event of problems.
Time-Triggered Data: Measurements or actions can be triggered at a specific time. This allows synchronized operation across multiple devices, for example, vibration sensors.
Process Variable Trends: Can be sent as 12 sequential time-stamped data points of the same process variable in a single packet, effectively multiplying communication throughput for the selected process variable. The values are stored in a circular file with a sample period of 1/32 ms, and can be sent before and after an event, broadcast to the system. The data values include device status.
Enhanced Data Publishing Modes: Include one-way publishing of process and control values, spontaneous notification by exception, ad hoc request/response, and auto-segmented block transfers of large data sets.
Dedicated Bandwidth: For high priority and periodic communications.
Shared Bandwidth: Provides elasticity for event traffic and ad hoc request/response maintenance and diagnostic messages.
Highly Secure Communications: AES-128 bit encryption with individual Join and Session Keys and Data Link Level Network Keys.
QoS Messaging: Applied to all messages to ensure complete and prioritized delivery.
Clear Channel Assessment: Channel-hopping, blacklisting, and adjustable transmit power support maximize coexistence between WirelessHART networks and other ISM-band equipment.
Command Aggregation: Multiple read commands can be embedded in a single transaction, giving faster configuration uploads.
Multiple Power Options: Long-life batteries, solar, loop, or line power sources.