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COMMUNICATIONS & NETWORKS FOLLOW A FUTURE-PROOF PATH
For process automation projects, the combination of Ethernet-APL, HART-IP, and PA-DIM technologies provides the most flexible and practical upgrade path for monitoring and real-time control, says Sean Vincent, FieldComm Group
intelligent field devices become available. Therefore, users are looking for better ways to access and act upon the associated data so they can improve operational and asset efficiencies. While new projects can be designed with a
D
clean-sheet approach for communications media and protocols, the reality remains that most projects are retrofits, or at least must interact with existing systems. As new technologies come to market, there is a transition during which not every product or product type is available in the new technology. This creates a need for blended networks. And even new projects may not be funded to initially take advantage of the very latest technologies, so designers are faced with the problem of how to incorporate essential digital technologies, while providing a practical upgrade path for improvements over time. Process users have long been familiar with
implementing HART over 4-20mA technology for bi-directional digital information exchange between smart field devices and a host system. However, there may be lingering concerns about what type of speed (bandwidth) and control features are needed in communications protocols for newer control applications, and how to transition to more contemporary Ethernet network media. Some users may be aware of the
deterministic performance goals promised by time-sensitive networking (TSN) initiatives, but it is not needed for all process automation applications. This is because virtually all process loops are thermodynamic in nature and therefore react quite slowly compared to the available network speed, and even the fastest loops can be handled by other more appropriate technologies. In fact, 4-20mA and traditional HART have always worked well in process plants, so digital technologies equaling or improving upon this speed will do so as well.
8 NOVEMBER 2022 | PROCESS & CONTROL
igital transformation for industrial process automation is progressing at an accelerating pace, as ever more
Three technologies have
been developed to address these and other issues, and their intersection provides the required solutions (Figure 1): • Ethernet-APL has
industrialised commercial Ethernet, delivering far- reaching connectivity and power for typical field devices. • HART-IP preserves existing
HART investments, extends the feature set with security and direct real-time control, and can be architected on any Ethernet media. • PA-DIM is a protocol-agnostic information
modeling specification developed collaboratively by many industry organisations, ensuring data is usable regardless of media, protocol, or field device supplier. Together, these technologies represent a
practical approach for implementing digital transformation for both existing and new systems, at the user’s preferred pace, while maintaining flexibility and protecting existing investments.
Media, protocol, data model Designers need to ensure that industrial communication transport media, protocols, and data models support current and future needs, especially with regards to legacy
devices, and possible future devices. Media – Traditional two-conductor 4-20mA
connections are a proven workhorse technology, although many users today would prefer the capabilities offered by Ethernet. However, installing commercial-grade Ethernet in process plants requires careful consideration of drop lengths, power delivery, and environmental conditions. These challenges are addressed by Ethernet
advanced physical layer (Ethernet-APL), which is based on Ethernet standard 10BASE-T1L two- wire Ethernet, plus extensions for intrinsic safety (IS) hazardous area deployment.
Figure 1: Ethernet- APL provides industrial-grade field connectivity
and communication performance, while HART-IP delivers the monitoring,
real-time control, and security
features process
automation users are demanding
Ethernet-APL effectively meets or exceeds 4- 20mA performance by providing a 10Mbit/s data rate with cycle times ranging from 10ms to 2,000ms, allowing up to 1,000m between network switches and another 200m to each field device, while delivering sufficient power for most instruments and even WirelessHART gateways. Ethernet-APL doesn’t reach commercial
Ethernet speeds, but it easily performs fast enough for process automation monitoring and real-time control. Standard industrial Ethernet switches are used for upper layer communications, and specific Ethernet-APL switches for the control/field network. Ethernet-APL technology uses one physical layer supporting the simultaneous
interoperation of many protocols. Protocol – Designing with a newer media
might lead one to believe that a different protocol would be in order, but one needs to consider that the massive installed base of HART instruments is unlikely to be ripped-and- replaced simply for a protocol upgrade. A better option is to implement HART-IP,
which remains backwards-compatible with the HART data model and tools, while providing greatly improved throughput for all industrial instrumentation and real-time control needs. HART has been popular in part because of the command data density it offers, providing valuable information in just a
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