WirelessHART производства Siemens

Looking at the large number of possible applications and configurations, we generally differentiate between two application types.

Background for the first type is the fact that according to estimates forwarded by the HART Communication Foundation (HCF), approximately 85% of the over 30 million HART devices in operation are used in an environment where only the 4 ... 20 mA interface rather than the HART interface of the device is used on a system level. Generally, data on the device can only be read on site. This is of particular disadvantage with devices that contain self-diagnostic functions - that’s what we call "stranded diagnosis".

In these cases, a WirelessHART adapter can offer assistance. Connected to the 4 ... 20 mA loop, it allows central access to the device based on wireless communication. It does not affect process control systems which continue to receive the measured value using the 4 ... 20 mA loop.

Central access is enabled through a diagnostic station with SIMATIC PDM and SITRANS MDS software.

Main advantages:

• Increases the availability of the plant
• Increases plant transparency
• Reduces costs due to employing a predictive rather than preventative maintenance concept
• Reduces travel time in larger systems based on central access to field instrumentation

In the second application the 4 ... 20 mA loop is omitted, all data including measured process values and diagnostic information are transmitted wirelessly to a process control system, for example.

Main advantages are:

• No planning and installation of data cables, resulting in significant cost reductions
• Higher system transparency due to additional and hitherto unfeasible installation of measuring points
• Process optimization due to flexible, temporary and cost-effective measuring points via wireless communication
• Utilization of proven devices by using adapters
• The WirelessHART meshed network also makes it possible to bridge longer distances

WirelessHART enables access to the following:

• Measuring and control values
• Parameters

of field devices with HART interface. These usually include pressure, temperature, level or flow transmitters or actuators.

WirelessHART allows for the following:

• wireless transmission of measured values and their status
• wireless parameterization and diagnosis of field devices

The WirelessHART adapter can be used to enable field devices with HART interfaces (that are designed for wired communication) for wireless communication. This allows users to continue using their proven devices while benefiting from and participate in addition in advantages offered by wireless communication.

This section introduces the application types described in the previous section in greater detail.

The figure below shows a typical situation for the first application type.

The adapter is connected to the 4 ... 20 mA loop, which is used to transmit the measured value to the control system, or transmit the setpoint to an actuator. The existing control system is not affected by the WirelessHART adapter.

The data, in particular diagnostic data from the devices is transmitted to the IE/WSN-PA LINK via the connected adapter and the WirelessHART network. The link provides this data to a diagnostic and maintenance station with installed SITRANS MDS software and SIMATIC PDM via an industrial Ethernet. Industrial wireless LAN can be used to save on the installation costs required for Ethernet wiring. An extensive product portfolio of Scalance W components is available for this purpose.

The functionality of related to the SITRANS MDS is described in great detail on page 9/18 of this catalog.

WirelessHART is integrated into SIMATIC systems parallel to the wire-connected devices with HART or PROFIBUS interfaces. In this case, the 4 ... 20 mA line to the control system is not required: all data, i.e. process values, parameters, diagnostic information and functions, is supplied to the automation system on a wireless basis. This is mainly useful for replacement and expansion measures related to existing systems, and of course also new systems, but also for temporary and mobile measurements.

The field devices are standard instruments with connected adapters, or those with integrated wireless communication.

In principle, a differentiation needs to be made between wireless communication and the power supply for the devices.

When installing a field device, the planning and installation of the data cable to the control system is usually considered a significant cost driver. This factor is greatly reduced when using wireless communication.

When using 4-20 mA/HART field devices with adapters, the question of powering up always arises - in contrast to battery-powered field devices with integrated wireless modules.

It is important to distinguish between two and four-wire devices here. Under certain circumstances, the SITRANS AW200 adapter can take over the supply of a connected two-wire device. The power consumption of the field device plays an important role here. If it is too high, an additional power supply becomes necessary. If more than one device is connected to the SITRANS AW200 adapter, an additional power supply is required.

Four-wire devices always require an additional power supply.

The properties of WirelessHART can be summarized as follows:

• Simplicity in handling and engineering
• Secure communication
• Availability in network

Simplicity in handling and engineering

• Utilize current tools, same workflow
  The description of devices and adapter is carried out using proven EDDL technology. SIMATIC PDM continues to be used as a tool.
• Multiple power supply options
  Devices can be operated externally with 24 V DC, external or integrated battery packs as well as solar cells. The option of using energy from the process or the environment has been researched at universities and industry for some time. It is expected that results and products will be available in the medium term.
• Reduced installation costs
  Depending on use, installation costs for data cables or power supply cables are not required.
• Coexists with other wireless networks
  WirelessHART only uses the ISM band in the 2.4 GHz area, since it is available across the globe. However, it is also used by Industrial Wireless LAN (IWLAN), for example. For this reason, a requirement to allow WirelessHART to co-exist with Wireless LAN networks was an absolute requirement when this technology was defined. This coexistence has been achieved by constantly changing the channels and hence frequencies. This is also called "channel hopping". Moreover, individual channels can be completely disabled through so-called "blacklisting", for example if they are locally used by IWLAN.
• Support of star-shaped and meshed network topologies
  Networks can be built in both a star-shaped as well as meshed structure. The advantage of star-shaped networks with a gateway as the centre is that it allows for fast update cycles. However, the range of the network is limited to a maximum of approx. 200 m without obstacles between the gateway and the devices.
  The advantage of meshed networks is their greater range, since each participant in the network is also a repeater and forwards the data of remote participants towards the gateway. The disadvantage: increased transmission times for data between the field device and the gateway.
• Faster commissioning
  Once the device is installed, it can usually be commissioned right away, since the usual waiting time for completing the installation of the cables does not apply in this case.
• Self-organizing and self-healing networks
  WirelessHART networks are automatically organized, built and administered by the Network Manager. Engineering is usually not required.
  The Network Manager is implemented in the IE/WSN-PA LINK, the WirelessHART gateway from Siemens.
  It calculates the optimal connection routes between the network participants and defines an alternative path that can be used in the case of disruptions in advance. In that sense, the network can be considered self-healing.
  In addition, the Network manager also defines the channels or frequencies to be used for all communication.
  Statistics regarding communication are compiled automatically and are available to users.
• Security - always active
  All designated mechanisms with regard to security are available automatically, and do not require any engineering.
• Make changes in the network without the need for configuration. The Network Manager automatically adds and withdraws participants to/from the network.

Secure communication

• Encryption - All information is automatically encrypted with 128 bit AES prior to transmission
• Specific keys for each data packet
• Data integrity - Each data packet is checked for changes or damage during transport.
• Device authentication
  Each device must know the network identification number as well as the join key. Otherwise the Network Manager does not include it in the network.
• Channel Hopping
  The channel which is used will be changed according to the Network manager’s specifications after each telegram. This provides an added level of security against spying activities.
• Failed authentification report
  Each unsuccessful attempt by a participant to join the network will be recorded and made available to the user.

Availability in network

• Communication based on IEEE 802.15.4-2006
  Wireless communication takes place on the basis of a proven industry standard. It allows for very minimal power consumption.
• Utilization of ISM band (2.4 GHz)
  This band can be used worldwide without incurring additional costs.
• Channel hopping overcomes disruptions
  Disruptions are usually limited to a small frequency range.
  By constantly changing the channel, it is possible to overcome the effects of such disruptions and hence increase the network’s reliability.
• Channel Black Listing permanently blocks disrupted channels.
  When operating another network at the same location, the channels occupied by that network can be blocked in the WirelessHART network.
• Self-healing network
  This aspect has already been discussed
• Redundant communication paths
• The Network manager automatically calculates redundant communication paths. This significantly increases the level of availability.

Software Overview

Applications 1 and 2 will require the following software products.

¹⁾ You can also contact your Siemens contact person.

²⁾ Other versions and accessories can be found in the product descriptions of this catalog.

More detailed information on the required WirelessHART software and hardware components can be found in the FI 01 catalog or at http://www.siemens.com/wirelesshart.