NAMUR Field Report: WirelessHART

12 July 2010

At the annual NAMUR meeting in November, 2009, Martin Schwibach of BASF SE Ludwigshafen presented to the assembled group of process automation experts a report of independent field testing of wireless instrumentation. Conducted in four areas of his own plant in Germany, the results have elevated the expectations of this new technology.

Pepperl+Fuchs took part in the field test with the WirelessHART Gateway and the WirelessHART Temperature Converter.
Pepperl+Fuchs took part in the field test with the WirelessHART Gateway and the WirelessHART Temperature Converter.

Clearly, the best and most secure way to transmit sensor signals to a host control system is through copper wires. It is unlikely that future developments will overturn this long-held conviction.

There are, however, many circumstances where installing a cable is problematic. And in the chemical process industry, there is a rich variety of these perplexing situations:  sensors, for example, that are located too far away from the control system and would be enormously expensive to connect. Then there are sensors located in areas difficult or dangerous to access, such as on a high tower or in some especially hazardous area. Or sensors located on rotating equipment, which are difficult to mechanically and electrically connect with stationary control systems.

With the advent of Hart 7.0 two years ago, the HART Communications Foundation began promoting what some consider the most important feature of this latest version: WirelessHART. For the first time, process users had access to a standardised method of installing wireless sensors in their plants, based on the well known and well accepted HART standard that had been in use for many years. On top of that, they had promises from a dozen vendors that products meeting the new wireless standard would soon be available.

NAMUR moves in
Anticipating that its member companies would have a keen interest in the developing wireless technology, and that it would hit the chemical industry sooner rather than later, NAMUR took steps to prepare for its advance. This positioning is well  summarised in two NAMUR Working Documents: NE 124 Requirements for Wireless Automation and NA115, IT Security for Process Automation Systems.

Some members of the organisation, in particular the large chemical company BASF, felt the urgency to investigate the use of the wireless communications. Instrument engineers at BASF decided actual field tests would be the best and quickest way to determine the value of the technology and assess its benefits.

There were two objectives in the field trials. First of all, the potential users wanted to see if there really was any added value for wireless communications in industrial plants. There were obvious advantages, but could it meet larger expectations? The investigations and assessments, it was decided, would focus on three key areas: mobility, flexibility, and the ability to replace cables. And secondly and more specifically, would the newly proposed WirelessHART meet the requirements set out in NE 124?
The field tests were conducted at the BASF facility in Ludwigshafen. They  included laboratory evaluation of performance characteristics and four implementations in operating process plant environments.

We present a summary of the results, as given by Martin Schwibach, Senior Automation Manager for BASF and Chairman of the NAMUR AK4.15 Wireless Automation Working Group, who was responsible for the field tests. There were four areas in BASF that conducted the experiments: a waste water plant, a water treatment plant, a reactor, and a cooling tower.

Six instrument vendors participated in the field trials, all of them providing prototype products: ABB, Emerson Process Management, Endress+Hauser, MACTek, Pepperl+Fuchs, and Siemens. The gateways used were connected to the various control systems with Modbus.

Waste water plant
The large distances, difficult environment, and rotating equipment were the challenges for this field trial; it would have been very difficult, if not impossible, to install standard cables to gather the data in this geographically very large waste water treatment area.

The large settling tanks in this application use rotating machinery to scrape material from the bottom and the sides of the tanks. The task of running wire from the instrumentation on the rotating scrapers to the control centre involved sliding contacts; these were not considered the ideal solution and in fact often proved faulty. There were level measurements taken with Endress+Hauser instruments, as well as some flow measurements on the reagent flow. The Krohne flowmeters were HART enabled, but the only indication of the process value was on the local indicator—it was not sent to the control system.

The field trial involved setting up eleven instruments, that all used standard 4-20 mA analogue signal transmission, to transmit their values wirelessly to a gateway

The legacy H&B control system was upgraded to accommodate the Modbus signals, but after that the system worked well, receiving signals it never had received before.

Water treatment
The second field trial was in a water treatment plant that was in the factory environment, used to treat water after it had been used in the process. Again the problem was to get signals from a rotating scraper in the settling tank. In this case, the procedure had involved identifying sediment concentration in the water by taking samples manually. This was done in order to log the slurry level. With wireless instrumentation this could be done directly and automatically by wireless level measurements, and eventually, the relevant pumps could also be activated wirelessly as a result of the level measurements. The trial involved two pressure transmitters, one flowmeter, one level measurement, and ten binary (on/off) signals, connected through a wireless gateway to an Emerson DeltaV control system.

The location for the third trial was quite different from the others: it was inside a older brick building seven stories high, built 50 years ago. As the plant had been in operation for many years it had accumulated plenty of equipment as well as pipes and ducts that make life more difficult for radio signals—not to mention the reinforced concrete floors separating sections of the process. A lack of cable trays added to the connection problems.

The engineers wanted to make some ‘temporary’ measurements, to get additional information about the process into the distributed control system, an ABB Freelance system. They installed 12 pressure transmitter and 18 temperature devices. Eventually, they wanted to be able to accommodate up to 50 wireless devices.

Most of the devices were mounted near to the reactor on level 2, and this is where the gateway was located. More devices were installed two floors above the reactor, but even though the radio signals had to travel through two concrete floors, they still provided a strong enough signal to use. A few devices on the top floor were not able to send their signals through five levels of concrete without serious attenuation, so the engineers placed a router out the window and managed to pick up the signal that way.

The trial was considered a success. In spite of the difficulties, reliable and robust signals were received at the gateway. It was a good experiment because it tested the  ability of moving signal around equipment. And it was a good application for battery powered instruments, since they only have to be in place temporarily, not for a 20-year life cycle. Nevertheless, as it is highly likely that the temporary instruments will become permanent, so battery checking will eventually become important.

Recooling plant
The fourth test involved a recooling tower located about 100 metres on a straight line-of-sight from the control room. There were no cable runs to the tower, so there was no way to directly monitor the load. Previously, the control room sent operators to the top of the tower for regular inspections, but these had not been adequate. As a result, last summer, there was some damage to the fan gearbox due to overheating.

For the WirelessHART field trial, eight temperature monitors were installed in the fan gearboxes to monitor the bearing temperature. These were located at the top of the tower. Inside the tower, three level sensors were mounted to keep track of the water level. The wireless gateway for all of these devices was installed on top of the control room building. Surprisingly, the level sensors could connect directly with the gateway, even though the signal had to penetrate the steel walls of the tower and travel for 100 metres. The gateway uses a Modbus protocol connection to send its signals to the central control system, an ABB Symphony DCS.

After conducting these extensive multi-vendor field tests, NAMUR reported that WirelessHART Communication provides the flexibility, security, robust performance, coexistence with other radio technologies and device interoperability within a WirelessHART network that its members should expect. 

‘Our tests prove that WirelessHART is an appropriate technology for applications within the NAMUR use class ‘monitoring’ for wireless sensor networks,’ said Martin Schwibach,

‘WirelessHART technology provides a good alternative where wired networks are too expensive or too difficult to install. This field test verified the alignment of the WirelessHART standard with the NAMUR requirements for wireless automation in process applications.’

Founded in Germany in 1949, NAMUR is an international user association of 121 member companies in the chemical/pharmaceutical processing industry.  NAMUR represents approximately 15,000 PCS experts, of whom approximately 300 are active in 33 working groups covering the fields of measurement and control, automation, communication, process control and electrical engineering over the entire lifecycle of systems.

*****  Sidebar: WirelessHART: From Technology to Products  *****
Dipl.-Ing. Gerrit Lohmann, Product Manager, Division Process Automation, Pepperl+Fuchs

During the final months of 2009, NAMUR and the HART Communication Foundation conducted a field test at the BASF plant in Ludwigshafen, which has been actively supported by Pepperl+Fuchs. The result: WirelessHART was proven to be a sustainable technology that can be used in mobile and flexible applications.

Field test clears the way
The NAMUR recommendation NE124 defines the requirement for wireless communication in process automation. One of the stipulations is an open and interoperable standard that is supported by many vendors. The only available standard today is WirelessHART. In order to operate the network seamlessly, all WirelessHART devices must be compatible and interoperable with each other. To ensure this, the HART Communication Foundation (HCF), NAMUR, and BASF teamed up with the leading manufacturers of WirelessHART products, including Pepperl+Fuchs, for a field test. With the help of BASF, NAMUR examined WirelessHART in terms of NE124. Pepperl+Fuchs took advantage of the test to determine how well our products conformed to the specification.

Pepperl+Fuchs took part in the field test with the WirelessHART Gateway and the WirelessHART Temperature Converter. The WirelessHART Adapter, which also will be offered by Pepperl+Fuchs, was provided by the cooperation partner Endress+Hauser.

Strengths and weaknesses
The results of the field test were positive, but they also revealed areas for improvement. The wireless communication and the security mechanisms proved to be extremely robust. However, there was some negative feedback regarding complete field device integration and plurality of battery solutions. As an improvement, BASF and NAMUR proposed a reduction in the amount of key performance indicators to enable easy network diagnostics instead of relying on vast amounts of statistics. Furthermore, the progress to eliminate all negative aspects is moving ahead at full speed.

Pepperl+Fuchs sees the result quite positively: the core technology can be considered as mature, and the wireless communication between devices of different vendors works well. Therefore, there is no fundamental obstacle that would hinder the use of WirelessHART. HOST integration has to be improved, but can be realized already today as Pepperl+Fuchs offers all necessary DTM and DD versions.

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