How to Get Unchained with WirelessHART™

Deploying any industrial wireless network requires addressing physical and security related issues, however WirelessHART™ offers several advantages over other wireless alternatives.

“Many control systems do not provide access to HART data,” says Yokogawa’s Manager, Field Instruments, Kaoru Sonoda, “and wireless technology can be a practical and cost-effective solution.” The solution is not to require control system vendors to revise, or end users to rip and replace existing control systems, but rather to enable them to do an end run around the problem. But increased demands on operators and maintenance demand a simple, effective solution.

Enter wireless. “Wireless technology has now been tested,” Sonoda continues, “and we believe it is capable of meeting the critical demands of the process industries.” Gareth Johnston, fieldbus communication specialist with ABB, says, “WirelessHART™ has been designed to simplify commissioning and lifetime support. The specification team always had it in mind to keep it as simple as 4-20mA. The result is that users can employ existing knowledge and software tools to support WirelessHART™ instruments and adapters.”


Figure 1. WirelessHART™’s mesh network architecture allows relatively easy installation, often without an extensive site survey. The self-organizing and self-repairing nature of a mesh network is well-suited to the industrial environment.


FLEXIBILITY BY DESIGN
According to Guido Stephan, director technology and processes, automation, and drives, sensors and communication, R&D technology & processes, Siemens AG, “WirelessHART™ communication will not replace wired HART, but it will offer access to diagnostic features of field devices and will allow additional applications not possible with wired devices.

” WirelessHART™ part of the new HART 7 standard, provides four ways to acquire data from field devices.

The first two are the traditional wired methods, with the primary physical variable on the 4-20 mADC loop, and the digital data (diagnostics, secondary physical variables, alarms, etc.) carried on the wire and pulled off at the control system or by a handheld calibrator.

The two new ways are:

  1. Wireless adapters for existing field device,
  2. WirelessHART™ field devices, with or without wires.

The wireless adapter is designed to retrofit any of the more than 24 million existing HART devices and provides wireless access to both the primary process variable and all the digital data from the device. A WirelessHART™ field device can be installed with or without 4-20 mA loop, can operate on battery power, and provides the same data access as the adapter. The wireless data is transmitted to a gateway, which connects to the control or asset management system.

As with all previous upgrades to HART standards, HART 7 and WirelessHART™ are completely backward compatible to any installed field device.

Now is probably a good time to reiterate that HART information – diagnostics, health, secondary variables, etc. – is communicated digitally on the same pair of wires as the 4-20mA primary measurement signal. Implementing WirelessHART™ simply provides another means of accessing that same HART information and more.

WirelessHART™ technology is based on IEEE 802.15.4 2.4GHz radio technology. The low power requirements of radios designed to this standard make them inherently suitable for low- power mesh networks, and because of international standards, these radios are cost-effective and available from multiple sources. To ensure conformance to international regulations, each radio includes a +10dBm amplifier that supports a clear-path transmission range of approximately 650 ft. (200m). Additionally, to extend the reach of the wireless network, each field device is required to communicate its own data messages, as well as being capable of passing on data messages received from neighboring devices. (See Figure 1.) The flexibility of WirelessHART™ provides multiple options for device placement to extend both the reach and reliability of the network.

PLANNING
Though the underlying technology of WirelessHART™ all but eliminates the need to conduct complex site surveys, no one is so naïve as to believe that network robustness, maintenance, and ease of future expansion (scalability) can be achieved without some degree of up-front planning.

To ensure a WirelessHART™ installation meets performance expectations, users should examine these four areas:

  1. Physical layout,
  2. Reliability, security and coexistence,
  3. Commissioning,
  4. Operation and maintenance.
PHYSICAL LAYOUT
When users begin planning an industrial wireless network, a plant walk-through reveals the physical difficulties of achieving clear-path transmissions of even a few hundred feet. Beta testers have reported that they have installed a gateway and carried a wireless instrument around to check location and quality of signal, rather than doing an extensive survey. Typically process plants have both intermittent and permanent obstacles that are likely to reduce, often times significantly, a user’s ability to establish wireless communication between field mounted devices. WirelessHART™’s mesh network simplifies this issue by providing multiple paths around obstacles, including the ability to go point to- point, not just mesh.

Having the flexibility to locate HART wireless adapters anywhere along the wire can simplify installation, maintenance, and security significantly, as in the case of the wireless adapters inside a marshalling cabinet where distances are minimal and intrinsic safety isn’t an issue (Figure 2). Likewise, a transmitter can be placed in an otherwise inaccessible location, say, under a large reactor, and the adapter located in a location where clear-path transmission is available. No other wireless methodology provides this flexibility. Once a physical WirelessHART™ device layout plan is developed, the next step is to examine reliability and security requirements. 		 
Figure 2. Fully developed, a HART network uses WirelessHART ™ to unchain the valuable diagnostic and process data locked inside existing systems and provides for future expansion with a choice of wired or wireless field devices.

GETTING YOUR FEET WET
You may have 50 or 5000 HART-enabled devices in your plant, and all of them are working, doing their jobs. You might not want to do anything to disturb them while they work until you have some more experience with the new WirelessHART™ technology.

So what to do?

You can gain experience with unchaining your HART data one of two ways. First, you could find a place where you’d like to monitor process variables, but because of the expense, you’ve never been able to justify doing it before.

BP’s Cherry Point, Wash., refinery did that in the most publicized beta test of Emerson’s SmartWireless system.

SmartWireless was designed as a WirelessHART™ precursor; that is, the system was designed to take HART data wirelessly, using hardware and firmware that approximated a best estimate about the final standard. Emerson publicly stated at the time and has reiterated since, that SmartWireless was capable of and intended to be upgraded to WirelessHART™ as soon as the standard was released and products were certified and available for sale.

Marty Gering, wireless data collection coordinator and wireless worker administrator for the refinery, was in charge of the demonstration installation. Although Cherry Point is actually the second-newest refinery in the U.S., there are many locations where large bodies of uncaptured data exist.

"This data is valuable," Gering said at Emerson Exchange 2006 when he discussed the installation, "but we can't touch it because of the expense of wiring and running conduit. Lube oil and bearing temperatures, among other values, are just left out of the picture."


One of the beauties of the WirelessHART™ standard is that the wireless adapter does not need to be located at the transmitter.



This field device is installed at PPG Industries’ Lake Charles, La., facility and transmits HART data entirely wirelessly. (Photo courtesy of Emerson Process Management)

Gering is at work on another project now: the tank farm. Cherry Point was built to be a 95,000 bbl/day refinery and has now become a 245,000 bbl/day refinery just by increasing throughput and optimization. The tank farm was built with only level and, in some cases, temperature sensors, and Gering wants to access that information wirelessly.

"We're beginning a new project to connect those tanks wirelessly with backup level. We also have hundreds of valves that we'd like to have positioner information on, as well as other pressures and temperatures," Gering announced. "We have mixers with motors we'd like to monitor current on, and lots of other things. We're looking at 300 points. We want to finish the engineering this year and have a big start on implementation by the end of 2007."

In addition to the wireless field device Gering is using, the second path to unchaining HART data is only now becoming available. One of the beauties of the WirelessHART™ standard is that the wireless adapter does not need to be located at the transmitter. It can be located anywhere along the 4-20 mA current loop.

As soon as adaptors become certified for compliance, you’ll be able to buy and try them out on existing wired HART instruments where you already know you want the data inside them. This will require NO rewiring and will not require taking the instruments or control valves out of service at all.

RELIABILITY, SECURITY & COEXISTENCE
Understandably, reliability and security ranked high among end-user concerns during initial discussions about deploying wireless technologies within the process industry. To that end WirelessHART™ addresses reliability and security concerns by using robust, well-proven, and highly effective techniques. In fact, when combined with built-in good neighbor/tolerant neighbor coexistence features, WirelessHART™’s use of fully proven mesh network routing techniques make it highly reliable.

Like any good neighbor, WirelessHART™ devices try to avoid bad behaviors, such as talking (transmitting) too loudly, talking too often, talking too long and/or using the entire frequency band, that affect others. Tolerance is a second characteristic of being a good neighbor. Within a wireless network, tolerance means that receiver nodes tolerate interference caused by other nearby radio frequencies or the occasional mistake, doing what is necessary to prevent data loss. WirelessHART™ transmitters can also use a power turn-down feature to reduce the reach and/or range of the signal to avoid network conflicts.

WirelessHART™’s robust security measures protect the network and its data at all times. They include message confidentiality (end-to end encryption), message integrity checking, message and device authentication, and secure procedures for devices joining the network. Industry standard techniques are used to provide authentication and encryption. WirelessHART™ also gives users the flexibility to apply their own network security strategy while preventing security from ever being disabled.

As you prepare to install and then commission WirelessHART™ systems, remember that your experience, training, and tools used for HART-enabled devices apply to WirelessHART™

WirelessHART™ devices are configured and installed in much the same way as they have been in the past, protecting your investment and maintaining the HART experience of being easy to use. After the WirelessHART™ adapters are installed, commissioning can begin. Actually there are two parts of commissioning–network commissioning and device commissioning.

NETWORK COMMISSIONING
Network commissioning begins when the gateway device is powered up and begins advertising. Being the first device in the network, the gateway establishes its own schedule that synchronizes nodes as each one joins the network.

But first, the network manager, which may or may not be hosted in the gateway device, must be configured with the correct network ID and device password(s). Once that is done, the network manager will automatically adjust the network’s schedule based on the requirements reported by each device as it joins the network.

Because WirelessHART™ provides an additional means of collecting HART information, the commissioning procedure is similar to that for wired systems. Using existing HART configuration tools, such as a HART handheld configurator or personal computer (PC) application, users only need to configure three additional parameters–device password(s), network ID and device refresh rate.

Existing handheld or PC applications can also provide a status display of the joining process and will quickly help pinpoint any communication issues. These devices also can provide access to diagnostics and supporting device calibration and maintenance operations.

DEVICE COMMISSIONING
The final step to commissioning a WirelessHART™ network is to complete device verification and conduct a loop test of any wired devices. WirelessHART™ devices need no 4-20 mA loop, and have a maintenance port for testing. Commissioning and maintenance are done via standard commands or DDL.

When so specified on the purchase order, device manufacturers put device tags and other identification and configuration data requested the user into each field instrument prior to shipment. After installation, the instrument identification (tag and descriptor) can be verified in the host system using a configurator (handheld communicator or PC).

Some field devices provide information on their physical configuration (e.g., wetted materials). These and other configuration data can also be verified, thereby ensuring the installed instrument is suitable for the application. Such verifications are important for regulatory health, safety, and environmental conformance, as well as ISO quality requirements.

Loop integrity is important when commissioning a device. For HART-enabled devices, analog loop integrity can be checked using a loop test feature, available in many HART devices. The loop test feature enables the analog signal from a HART transmitter to be fixed at a specific value so total loop integrity from device to indicators, recorders, and operator displays is correct.

Additional integrity can be achieved if the analog value of the primary variable (PV) is compared to the digital value being reported from the device. For example, someone might have provided an offset to the 4-20mA analog value that has not been accounted for in the control system. Comparing the digital value of the PV to the analog value verifies the entire loop is properly calibrated.

Consistent with wired HART, the WirelessHART™ specification allows wireless devices and wired devices using adapters to simulate a process value to accommodate loop testing, allowing verification of data across the network, through the gateway, and into a host application. A wireless device can be set to transmit a fixed value in order to conduct this important test.

Many HART configurators provide easy ways of collecting, archiving, and/or printing commissioned device information. Because WirelessHART™ uses the same configurators as hardwired HART, existing procedures for collecting and recording “as-installed” device configuration data, calibration records, and other device records remains essentially unchanged.

WirelessHART™ is the first open and interoperable wireless communication standard designed to address the critical needs of process industry users. It has been carefully designed and thoroughly tested to provide reliable, robust, and secure wireless communication in real-world industrial plants.

WirelessHART™ provides new ways to gather information on process parameters and monitor the performance of plant assets in areas that have previously been difficult to achieve either technically or cost-effectively. It extends the power of HART into areas that were difficult to reach with conventional wired systems, and it provides low cost digital access to existing HART devices.

 
   
HART® is a registered trademark of the HART Communication Foundation