By Scott Broadley, Broadley-James
A flexible manufacturing environment has become an important element in nearly every manufacturing sector. It's no different for the bioprocess industry.
We can create greater manufacturing flexibility through the use of portable, skid-mounted process equipment interconnected and controlled with digital fieldbus technologies.
In some applications in the bioprocess industries, the introduction of single-use vessel and separation technology provides further flexibility in process design and operation. However, the fixed-wiring practices of a traditional installation limit many of the potential benefits of a portable environment.
We can show how fieldbus technologies used on a skid will reduce wiring complexity. But physical connection points into the control system inherently restrict equipment movement and create their own maintenance issues.
Our application of WirelessHART technology provides our customers a new flexibility in manufacturing that addresses both monitoring and control applications. A major benefit of WirelessHART is the user may move the equipment with no impact on control system configuration.
However, when applying any new technology, it is important that we consider whether the technology is appropriate for the application. We've applied WirelessHART to a portable, skid-mounted, single-use bioreactor.
Skids Know Their Place
Skid-mounted equipment is commonly used to speed on-site construction of a new manufacturing facility. At Broadley-James, we manufacture small, portable, bio-reactor skids with instrumentation and automation system attached. We also make some of the components—sensors, for instance—that make up the parts of the skid. Emerson provides most of the instrumentation and automation system.
Oftentimes, the equipment on the skid is customized to customer preferences for materials of construction, field devices, interconnecting piping and process design and equipment and support structures. Skid-mounted packaged equipment can include a broad range of designs for process and utility applications such as refrigeration units, vacuum pumps, heat exchangers, chemical-injection systems, reactors and filter packages.
In an industrial plant, skid-mounted equipment normally represents a small portion of the process and must be integrated into the plant distributed control system (DCS) to enable coordinated plant operation. To provide consistency in maintenance, the field devices may be directly integrated into the plant DCS. In older installations, this integration required that wiring from each field device be brought into a termination panel on the skid and wiring run for each field device from the termination box to the DCS. With the adoption of Foundation fieldbus by major DCS suppliers, the wiring between the termination panel and the DCS can be greatly simplified.
However, when a skid is portable and routinely moved within the plant, even a few pluggable connections to the DCS can become a maintenance issue. Also, when a piece of equipment is used in multiple locations, the design of the DCS software often doesn't allow movable connections without added configuration complexity.
WirelessHART field devices solve many of these issues since the connection to the DCS is independent of its physical location. Through the use of WirelessHART field devices, a physical connection to the DCS is no longer required (Figure 1).
As when applying any new technology, it is good to understand the devices that are available for WirelessHART and how they can be integrated into the control system.
The HART Communication Foundation, its member companies and industry leaders developed WirelessHART technology to meet the unique requirements of wireless networks operating in process plants. The integration of WirelessHART field devices into a DCS is done through a WirelessHART gateway. The gateway provides access to the WirelessHART network through one or more access points. In most cases, the gateway also will contain the network manager that handles communication bandwidth and routing. This network manager is responsible for the creation of routes that can be used to perform communications with the network devices.
The network manager continually collects data from devices and uses this information to adjust routing and scheduling. It establishes the communication schedule to transfer process data, alerts, diagnostics and other traffic to the gateway for access by the plant automation host. For network devices such as actuators, interlocks or any device that affects the process, the network manager establishes scheduled communication that the plant automation host can use to send setpoints and outputs to the field devices.
As field devices are installed in the field, they form a mesh network with the gateway. Alternate paths for communications are established automatically to avoid a single point of failure. When only HART transmitters are available for a measurement, a WirelessHART adapter can be used to make information in the HART transmitter or positioner available over the network.