meaning that each instrument functions both as a receiver and transmitter. All the instruments in the network eventually send data to a gateway, which is used to join the wired network and connect to a host system, in this case, a process historian. The 2.4 GHz radios in each wireless device normally have a relatively short distance range, but this can be greatly increased because the network passes data packets from device to device in hops, relaying it from the most distant instrument to the access point and gateway. This functionality provides the performance needed for a site where devices are spread over a large area, such as a mine. Its self-organising capability allows the network to adjust itself as needed if there is interference, or if individual devices go offline. In areas where the device distribution is especially thin, adding a repeater (a transmitter without an associated instrument) strengthens the network by adding additional paths. For this project, four repeaters were added to improve network density and add more communication paths. Reliability of the network since startup has exceeded 98%.
Interfacing with the historian
As mentioned earlier, data from the field instruments is captured and recorded by a process historian running on
servers in the site’s operating building. Here, operators can see what is happening in the field and reset totalisers, although opening and closing valves or turning individual pumps on or off is still a manual operation. Eliminating manual rounds allowed site managers to deploy personnel on higher-level tasks to improve and optimise production. Operators, engineers, and environmental department personnel can compare what is happening at multiple points as needed – they can scroll through historical data quickly and easily, rather than sifting between manually-recorded reports. In addition, ready availability of this operational data informs all stakeholders of key performance indicators related to environmental, sustainability, and safety objectives. When first deployed, operators often compared their manual readings from the local instrument displays against data collected on the network, but quickly found this was not necessary as the data always matched.
Looking ahead
The company is already looking at areas where WirelessHART can support more effective data collection over even longer distances. Many instrumented application points are spread across the site that need to be monitored more closely, calling for WirelessHART networks. These additional projects will require communication with remote field instruments installed six miles or more from an access point. Since new instrumentation will be involved, facility personnel are looking at using Rosemount transmitters with native WirelessHART connectivity, rather than adapters. Parabolic and other directional antennas (Figure 5) able to increase range will be part of this deployment, so additional testing is underway to verify the capability, but the success so far bodes well for the next step. This WirelessHART deployment has saved the company thousands of hours previously spent by staff making manual rounds to gather data from instruments. Safety has improved because personnel now spend less time in the field. Finally, collecting data more often and with greater reliability has improved operations through performance optimisation.
Conclusion
Figure 5. Some challenging applications call for Emerson’s Rosemount native WirelessHART pressure transmitters, combined with specialised long-distance antennas.
16 August 2023 // global mining review
Most mining sites are spread out over large areas, making wired communication between instruments and host systems impractical. As shown in this application example, this challenge can be overcome by installing a wireless network, for a fraction of the cost of hard wiring. With WirelessHART, instruments can be purchased with this protocol natively built in, and existing instruments can be joined to the network by adding an adapter, which converts the instrument’s 4-20mA output to a wireless signal. The result is a network that can cover very large areas reliably, supplying the data needed to improve operations and safety.