IIoT and Device-Level Network Design

Emerson's Dan Carlson


Wireless instrumentation has been available for manufacturers for more than a decade. Sensors have expanded beyond traditional measurements such as pressure, temperature, level and flow to measurements such as acoustic, vibration, conductivity and more. These easily installed Industrial Internet of Things (IIoT)-based field devices make more than monitoring and control possible—they make real-time personnel safety, reliability, energy efficiency improvements possible to help deliver greater performance.

Control Engineering: Bring IIoT capabilities to refineries and process plantsIn a Control Engineering article, Bring IIoT capabilities to refineries and process plants, Emerson’s Dan Carlson highlights considerations for building a solid foundation with device-level networking best practices.

Dan opens highlighting the capital expenditure side benefits of wireless instrumentation:

WirelessHART deployments reduce instrumentation installation costs by eliminating expensive cabling. The cost of adding a wired instrument in a refinery can range anywhere from $5,000 to $50,000.

He describes the global IEC 62591 WirelessHART standard.

This wireless protocol is based on the traditional 4-20 mA wired HART protocol. It leverages existing instrumentation practices for deploying and maintaining instrumentation, but without the traditional cost of running signal wires and supporting infrastructure, including junction boxes, cable trays, marshalling cabinets, and others.

A key component in this network architecture is the gateway. It:

…manages the wireless network. It also integrates process data and diagnostic data into the host system via a hardwired Modbus RTU, Modbus TCP, OPC, HART IP, or Ethernet IP connection-as well as with other vendor-specific protocols.

Life of the batteries powering these wireless devices is based on the update rates they provide back to the network. Dan advises that the:

…usual rule-of-thumb suggests the fastest refresh rate for a wireless transmitter should be eight seconds. Applications demanding an almost constant refresh rate also are likely deemed critical enough to need a wired instrument. Field experience suggests most WirelessHART users go with much longer refresh rates, often 60 seconds, to minimize power consumption. At that rate, the internal power module can easily last 10 years.

Gateways can be a single point of failure, so most manufacturers use redundant pairs. As these device-level networks grow:

…most plants adopt multiple networks run in parallel. Keeping similar devices associated with each other makes it easier to send data to the right destination. This segmentation must be approached methodically to ensure appropriate numbers of devices are on each network to support effective meshing, with enough redundant paths for individual transmitters to communicate with each other.

Read the article for more best practices on building robust networks considering distances and density of the devices on the network. Dan provides rules of thumb for distances based on the level of obstructions between devices at points in the mesh network.

These added wireless sensors are at the heart of most digital transformation efforts along with the data flowing from smart devices connected to digital communications fieldbus networks. Many manually performed work processes to improve safety, reliability and efficiency can be automated to drive performance levels higher.

You can connect and interact with other wireless and digital transformation experts in the IIoT & Digital Transformation group in the Emerson Exchange 365 community.

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