Installing new instruments in an existing process plant can provide information and improve the performance of steam traps, heat exchangers, pumps and other equipment. However, it is sometimes difficult to justify these projects with conventional wired instrumentation due to high cost, lengthy installation time and required downtime.
Wiring infrastructure is not needed for battery-powered WirelessHART installations, as a wireless mesh network consisting of a gateway base station and repeaters replaces it. Including wireless can help justify a project as the incremental solutions and applications that can be added to the wireless network can demonstrate benefit beyond the original project scope.
A WirelessHART project typically involves two or three parties: the end user, the systems integrator designing the system and installing the equipment, and the equipment vendor supplying the wireless instruments and communications infrastructure. The systems integrator and wireless equipment vendor may be the same company.
The end user typically produces a functional requirement specification that describes applications, wireless instrumentation and the necessary infrastructure for the wireless network. The end user must determine what points are to be measured, and then work with the wireless instrument vendor to ensure that appropriate devices are selected for both process and diagnostic measurement functions.
Because each WirelessHART instrument does not require wires for signals or communication, and often neither for power, the financial calculations determining whether a measurement should be made are very different than with wired instruments. The significantly reduced cost for a wireless measurement should be taken into account when deciding whether or not a particular parameter should be monitored.
In addition to flow, pressure, level and temperature measurements in conventional applications—such as on tanks, vessels, reactors, pipes and similar process equipment—WirelessHART makes it possible to consider applications previously too expensive to implement with wired instruments. These include measurements in remote places, or those previously considered uneconomical for monitoring.
After the functional requirement specification is completed, equipment must be selected. Wireless field instrumentation can be used for all non-critical process measurements, and for control loops that are not fast acting. It can also be used in hazardous locations. The devices that are certified to the relevant protection level for the hazardous area reduce or eliminate the amount of supporting wired infrastructure installed in the hazardous area.
All non-SIL independent protection functions can be implemented with wireless. These will form part of any layers of protection analysis (LOPA) assessment. Many wired process measurements requiring redundancy might be better served with wireless instruments, as they provide a second and completely independent source of measurement. This determination should be made during the HAZOP study.
It is important to ensure that security best practices are used in the design of the wireless network and gateways. If a separate Wi-Fi infrastructure is not part of the project specification, then the installation contractor may benefit from temporary Wi-Fi access points to aid field commissioning using mobile worker client applications.
For more information, please visit the FieldComm Group website.
