Applications

WirelessHART instruments provide the same level of remote process and diagnostic information as the hardwired (4-20mA loop) versions. It is the independence from the hardwired infrastructure which offers greater flexibility when compared to more traditional 4-20mA loop installation.

This page describes how WirelessHART enabled devices can be applied within process applications and the potential benefit available.

WirelessHART devices
WirelessHART features can be accessed by either adding a WirelessHART adaptor to an existing 4-20mA HART instrument or, using an instrument with WirelessHART capability built in.

Common Applications

The following examples of WirelessHART applications have been categorized as:

• Process Monitoring and Control
  • The process value(s) are transmitted wirelessly and may supplement the 4-20mA traditional signal
    • Multivariable Instruments
    • Short term Ad-Hoc measurements
    • Tank Level gauging
    • Plant/Instrument infrastructure upgrade
    • Supervisory and Non-Critical Process Contro
• Asset Management
  • Device diagnostic and maintenance conditions are available to the host system
    • Device Support
    • Maintenance
    • Diagnostics

• Health-Safety and Environmental Monitoring
  • Cost effective solution to measure health-safety and environmental conditions
    • Area Gas detectors
    • Water Effluent
    • Gas Emissions
    • Relief valves
    • Steam traps
    • Safety showers
      

Process Monitoring
The following applications demonstrate how WirelessHART can be used to provide process information to a host system. In all the following applications it is the HART process value(s) which are transmitted. However the complete range of instrument support and asset management features is available remotely as well.

Multi-Variable Instruments (Coriolis flow – MV Pressure …)

Hardwired (4-20mA) Instruments can only report a single process variable without the advantage of HART communications. In the past, the host system would require I/O modules or multiplexing devices capable of passing HART commands to and from the field Instrument. Retrofitting of such equipment may be undesirable and expensive.

The WirelessHART solution overcomes the difficulty of rewiring marshalling cabinets by offering an alternative wireless route to the host system. It is possible to add a WirelessHART adaptor to existing field instruments which retain the 4-20mA signal while providing host access to the four process variables provided by the HART standard. The use of instruments with built-in WirelessHART capability provides a solution with the added flexibility that they can be self powered.

The advantages are

• Add multivariable data access to individual instruments as required
• No re-wiring of marshalling cabinets to accommodate HART multiplexers
• Primary measurement can be maintained via the 4-20mA signal while the digital process variables are accessed via the WirelessHART adaptor
• HOST systems uses standard HART commands, HART applications and HART tools to read the process values (Universal Commands)
• Apart from reading the process variables remotely, you can also access all the device functions as available via the HART commands. This includes diagnostic messages and the ability to up/download configuration remotely.

Considerations
If the primary measurement is required at a rapid update rate (less than 1 second), it is best to hardwire (4-20mA) this signal to the HOST and connect a WirelessHART adaptor to allow the access to the other device values.

Ad-hoc measurements
(Temperature profiles / columns / tanks / reactors)

In some situations it is desirable to increase the visibility of process conditions by adding new measurement points around the plant to improve product quality, plant safety or process reliability. Without sufficient spare capacity within existing cable runs and I/O modules, this may be an expensive option with traditional wiring.

The WirelessHART solution utilizes self powered instruments to report the new process measurements. This could take the form of, simple to fit, contact temperature monitoring devices. The costs saved (running cable – Controller Input modules) during installation could make it economically viable to add several WirelessHART process measurement points to improve your process visibility.

Considerations
The presence of WirelessHART devices in the vicinity provide an opportunity to add asset management (maintenance reporting) features to critical devices by the addition of WirelessHART Adaptors.

Tank gauging
For level monitoring in a tank farm, WirelessHART provides a solution without the cost of running new cable.

In this case, the installation of self powered WirelessHART level gauges to a gateway connected to the Control System would be recommended.

Considerations
It is important to consider the location of the wireless devices on each tank so that a wireless network can establish itself. It may be necessary to add routers where plant equipment could block a wireless path.

A self healing mesh network will benefit this type off application where temporary obstructions can occur.

Tank level update rates are usually low and so wireless battery life is likely to be longer than for many other applications.

Upgrading Instrument infrastructure
As ageing instrumentation and infrastructure begins to effect plant availability there are often several problems to overcome.

1. Use supplementary process measurement to improve process visibility
   The low cost of installation offered by WirelessHART will allow the addition of process measurement points around the plant to improve process and equipment visibility and ultimately reduce product variation.
   
2. Replace obsolete instruments as they fail
   When upgrading an obsolete pneumatic or obsolete instrument, a WirelessHART replacement provides rapid and low cost alternative to a wired solution.
   
3. Replace obsolete instruments by plant section
   Typically the replacement of pneumatic instruments with modern intelligent devices requires removing the old pneumatic runs and replacing them with signal cabling. A full or partial WirelessHART installation reduces cost while providing a superior level of diagnostic/maintenance reporting

Supervisory Process Control implementation
It is likely that the initial WirelessHART installations will be used within applications involving process monitoring and not the execution of PID control functions. This does not indicate that a wireless solution cannot be used for process control as you can see in the following example of a batch reactor.

Chemical Batch Reactor
For example, a chemical batch reactor may be instrumented with the measurements and actuators shown in the following example:

WirelessHART offers features which allow it to be applied to appropriate control and measurement tasks. Of these features, perhaps the most important is the ability to select update rates based upon the task required (see the table below).

Asset Management
WirelessHART devices provide the same support for Asse as wired HART devices. The wireless connection provides access to all device parameters without the need for parallel wiring in the marshalling cabinet or other hardwired connection for systems that do not have an integrated HART interface. The same asset management software can be used for both wired and wireless devices providing continuity throughout the entire plant. The following describes device maintenance and diagnostics.

Device Support

• Configuration
• Database management
• Commissioning

As with a traditional wired HART device, the digital wireless connection provides device support. A wireless device can easily be configured remotely using an application connected to the gateway eliminating the need to be directly connected to the field device with a handheld. If a wireless handheld is available, configuration can be accomplished in the field without the need to climb to hard to reach locations.

Maintenance

• Calibration
• Record valve signatures