Your First Wireless Network

Rules of Thumb for Manual Network Design

Although a new breed of automated tools is available to streamline wireless network design (see sidebar, p7) manual rules of thumb can also be used. Starting with a scale layout of the process unit or area, draw connecting lines between each planned wireless device and neighboring wireless devices that meet any of the following criteria:

As a best practice during the design phase, each wireless device should be connected to three other wireless devices, even though the wireless connection distances may vary by direction. Having three connections during the design phase ensures each device has two alternate connections after installation.

If a wireless device does not have three connections during the design phase, then add additional measurement points or use a range extender to fortify connectivity.

There should not be any connectivity lines between wireless devices in the following situations:

Australian Terminal Keeps Bitumen Flowing

At Terminals Pty.’s facility in Geelong, Victoria, Australia, bitumen is unloaded from ships through a pipeline 3,000 ft (900 m) long and 8 in. (200 mm) in diameter. Because bitumen solidifies at ambient temperature, electric heaters operate all along the pipeline to keep the bitumen hot (160 ºC) and fluid. If a heater fails, a cold spot could form, causing the bitumen to solidify and plug the line, an expensive problem.

“We needed to monitor the bitumen line,” according to Bitumen Terminal project manager Joe Siklic, “to make the operators aware of cooling anywhere in the line from the ship to the storage facility, which could result in an emergency shutdown. Any delay in unloading could keep a ship at the pier longer than planned with demurrage costing up to $30,000 per day.”

The terminal chose wireless technology, Siklic says, for its lower initial cost and minimal maintenance as compared with hard wiring. Eight Rosemount wireless temperature transmitters are evenly spaced along the pipeline, sending temperature readings on one-minute intervals to a Smart Wireless Gateway on shore that channels data to the AMS Suite predictive maintenance software used for instrument configuration and performance monitoring. The collected data also are forwarded to a SCADA system in the terminal control center via fiber-optic cable.

Due to the self-organizing nature of this technology, each wireless device acts as a router for other nearby devices, passing the signals along until they reach their destination. If there is an obstruction, transmissions simply are rerouted along the mesh network until a clear path to the Smart Wireless Gateway is found. All of this happens automatically, without any involvement by the user, providing redundant communication paths and better reliability than direct, line-of-sight communications between individual devices and their gateways.

“This is an ideal application for wireless,” Siklic says. ”Since numerous paths exist to carry the transmissions, the network would easily compensate for a transmitter failure, and the operators would be warned. This wireless network has proved to be reliable, compatible with existing control equipment and cost-effective.”

New Tool Eases Wireless Network Design

While there are well-developed rules of thumb for manually validating that a WirelessHART network configuration will provide adequate connectivity (see sidebar, p5), a new engineering tool from Emerson Process Management now makes the job even easier.

Called the AMS Wireless SNAP -ON, the tool allows users to drag and drop devices and gateways onto a plant layout, then easily validate and optimize the network design against known best practices. Further, once the network is up and running, the tool allows the user to maintain the network easily by graphically displaying network traffic and diagnostic data.

This view is useful for detecting any potential weak points in the self-organizing network.

To design a wireless network using the AMS Wireless SNAP -ON, the user first imports an image of the process area where the network will operate (top image). Then he or she sets the image’s scale by drawing a line across any two points and typing in the distance. The user then designates whether the process area represents an environment of high, medium or low density of process equipment.

The user then drags and drops desired WirelessHART devices and gateway(s) onto the plant layout. Then the user automatically validates the design against best practices planning parameters (middle image). In this image, the red circle indicates a violation of best practices that might be addressed by adding another measurement point or wireless repeater to complement current communication paths.

For wireless networks already in operation, the user is able to see the device icons from the HART Device Descriptor (DD) and the self-organizing network communication pathways (bottom image).

LAPEM Streamlines Efficiency Testing

On behalf of Mexico’s Federal Electrical Commission (CFE), wireless technology is helping to streamline the measurement of thermal efficiencies at power generating units throughout the country.

LAPEM, the Testing Laboratory of Equipment and Materials, has five analysis teams that set up temporary measurement facilities at each of 140 power plants, but wanted to increase the frequency at which each plant was tested. In contrast to traditional wired measurements, one team’s easy establishment of a temporary wireless network made it possible to increase its productivity and plant coverage by 10 percent. This led to an annual revenue increase of US $512,000 for the unit. It has also improved the revenue of the Federal Electrical Commission by pushing higher output for each plant while reducing costs.

The ease of use and the reliable performance of Emerson’s Smart Wireless system resulted in a decision by the Laboratory Analysis group to equip all five of its analytical teams with wireless instrumentation. Their productivity is expected to increase by another 40 percent with faster turnaround time between services. As a result, all five teams should perform 25 more assessment services per year, producing an extra US $1,375,000 annually without adding personnel. Each of the 140 power units can now be visited and analyzed every other year.

“In the past, we could only cover about 50 plants per year,” said Oscar Martinez Mejia of LAP EM. “We needed to reduce turnaround time at each plant in order to reach every plant on a two-year cycle. Emerson’s Smart Wireless made it possible for the team equipped with wireless devices to cut their on-site time by one-third, enabling them to complete more services in a year’s time and proving the value of wireless.”

“It takes 15 days to install and commission wired instruments, take the readings, and tear down the setup,” Martinez Mejia said. “Then, another week is needed for reporting and other activities before a team can move on to the next plant. In the future, they will be able to cover 75 plants per year, because the on-site work can be done in just 10 days using wireless devices.”