Josh HernandezPicture a computer sitting on a desk: main processor enclosure, monitor and keyboard. It has no networking cables going anywhere and no Wi-Fi. Not even a phone-line modem. It’s alone and completely isolated. How long has it been since you saw such a thing? 20 years? Longer?
These days, the thought of an isolated computer is difficult to imagine. Whether at home, in an office or on a plant floor, connectivity matters. The ability to provide connectivity for users to reach other users and access the web is now a requirement for most computers. The question isn’t whether to have networks, it’s what are the best kinds of networks, and how can they be used most effectively? What are the best network designs to create and support a truly connected facility?
In manufacturing, the demand for control, data gathering and analytics is constantly driving the need for connectivity. The benefits to companies are substantial:
- Increased uptime and productivity
- Reduced costs
- Real-time decision making
- Improved mobility
- Improved safety
Networks have to move ever more critical data, which means more capacity and simultaneously, improved security. Network managers have to deal with a wide variety of manufacturing assets which have their own ways of communicating and presenting data. This can lead to some interesting translation challenges as they try to get disparate devices and systems to talk to each other.
Figure 1: Process plant networks tend to be more complex than discrete environments.Networks need to connect components such as programmable logic controllers (PLCs), remote terminal units and other automation system elements. The reach of networks is getting deeper all the time as the number and variety of components grows. This is critical to implementing modern manufacturing concepts where it may be necessary to make regular adjustments to products and processes to keep up with changes in market demand, feedstock changes and other factors. As mentioned, most of the discussion related to connected factories relates to discrete manufacturing—but what about process environments?
Connected Versus Connectivity
Process manufacturers like to point out that they’ve had connected plants for a long time. But in many cases, this just means most analog field devices are connected to a distributed control system (DCS). The only way to gather information from them is through the DCS, which depending on its age, may be much easier said than done. Getting information from a process historian may help, but outside of the most modern DCS architectures, platforms designed 15 or 20 years ago did not anticipate the need to have the kind of connectivity necessary to send device-level information to other users within the company. Making it happen often requires extensive custom code writing, if it can be done at all.
Given the age of most DCS installations, many companies are in trouble. Even the PLCs and sub-controllers working under the DCS may be too old to offer Ethernet connectivity, making it difficult to reach anything below Level 2 (L2) as depicted in Figure 1. As a practical matter, some of these components may have been updated individually. This helps, but in most plants and facilities this type of functionality is hit-or-miss.
So if a process manufacturer wants to reach down deeper and gather information directly from devices at network Level 1 and Level 0, are there any practical options? The answer usually requires going around existing legacy networks. The most practical approach is using a wireless instrumentation network to supplement the existing wired system. It has to work hand-in-hand with wired and wireless plant Ethernet networks for maximum effectiveness.
Talking to Field Devices
Most DCS I/O is designed to only handle analog or simple binary (on/off) data. However, most field devices installed in the last 15 plus years have the capability of sending supplementary data via HART. Since the I/O system usually can’t handle this data, it gets stranded at the device, but a wireless adapter can be added which can send this data via WirelessHART. Adding the adapter does not interfere with the existing wired I/O, and the field device can send the same data as it always has to the DCS. The primary process variable and supplementary data can be sent simultaneously via the WirelessHART signal to a gateway.
The gateway does not have the constraints of the native DCS I/O. Using a standard Ethernet interface with the existing IT infrastructure, it can send data anywhere, all the way up through the levels to the corporate network, and even to the internet if this functionality is enabled. It can also interface with the DCS, which means a WirelessHART instrument can be added to the process unit and send its data via the wireless network. The WirelessHART network can serve both requirements as needed. It can also provide a path to add instrumentation to a process unit when the conventional I/O is fully saturated.
WirelessHART networks are self-organizing and secure, and can be fully redundant. This may come as a surprise to network designers and managers used to dealing only with Ethernet, but this makes WirelessHART an important tool able to extend the reach of manufacturing networks far closer to individual field devices at the edge. Effective decision-making may hinge on having detailed information, and getting it depends on the right type of connectivity at all levels.
Josh Hernandez is a wireless product manager for Emerson.
