Process engineering teams are currently facing a difficult decision, both in brownfield and greenfield projects. For more than two decades now, process automation plants have been able to choose from many new manufacturer solutions like smart field devices, flexible I/O systems and proprietary Ethernet-based systems.
Unlike office IT systems, which are both open and easy to upgrade, the industrial OT (operations technology) space cannot offer the same longevity. Additional hurdles to industrial electronics products for hazardous industrial environments include ongoing testing and evaluation according to the latest published revisions of the IECEx standards, as well as increased regulatory burden related to cyber security and enhanced safety requirements.
So what choices do process automation engineers currently have? Simply put, conventional I/O, fieldbus, and soon, Ethernet-based I/O. Communication methods have evolved from mechanical (pneumatic) to electronics with the 4-20 mA current loop, to a wider serial (RS-485) and fieldbus technique. The 4-20 mA option remains the most used method, with more than 50 years of deployment proving it to be the convention for varying signals.
Conventional I/O is a combination of discrete on/off signals (known in the industry as digital I/O) and 4-20 mA analog I/O signals. And in process automation, the flow, pressure, level and temperature measurements are important variables in any application. The HART communication protocol has been part of a small renaissance over the past few years, as it provides many valuable device details to users who can extract additional data without compromising the working process. Plus, HART has been available built-in (at no additional cost) in many field devices over the years.
Process fieldbus systems based on IEC 61158-2, such as Foundation Fieldbus and Profibus-PA, could have been deployed in the past 25+ years, but they never completely replaced the prior I/O technologies.
Now, as fieldbus faces declining market acceptance and product availability, it is being phased out. This has created great concern for end users who may have recently signed up for a technology that might not be available much longer.
New options with Ethernet-APL
Over the past few years, four industry-leading standards development organizations (SDOs) have collaborated with 12 leading manufacturers of process automation technology, leading to the creation of the Advanced Physical Layer, known as APL. Based on the IEEE 802.3 cg specification for a two-wire, Ethernet-based technology with distances far beyond regular office Ethernet and fulfilling the need to go 1,000 meters (3,280 feet) with 10 Mbit/s data speeds, Ethernet-APL is a modification of the Single Pair Ethernet standard. Because it is just a physical layer, it supports any industrial Ethernet protocol.
