Data acquisition undergoes a paradigm shift
October 17, 2013 by Kristina Urquhart
Is “Configurable I/O” making fieldbus technology obsolete/redundant? My definition of Configurable I/O is a termination assembly that has sufficient flexibility so that the individual signal termination (typically the pair of wires connected to the field device) is independent of the I/O card residing in the backplane.
Traditional I/O systems have field junction boxes where a range of signals are gathered by a single multiconductor cable, which then runs to the interface room and typically terminates in a marshalling cabinet. There are two reasons for a marshalling cabinet. The primary one is to separate individual signal types on the multiconductor cable from field back to the individual signal types so that they can be terminated on the correct I/O card. The secondary reason is that it is often the demarcation point between the field and the control system with knife gate and/or fused terminal blocks for isolation and protection. There is, of course, a significant amount of engineering and labour needed for terminations to manage all of these signal cross-overs in the marshalling cabinet, as well as the real estate factor, that makes it an obvious target for elimination.
Fieldbuses that have only one signal type eliminate the requirement for the marshalling cabinet, and now many control system suppliers are offering Configurable I/O, which also makes the marshalling cabinet redundant — for signal cable management, at least. Three DCS (distributed control system) suppliers (Emerson, Honeywell and Invensys) offer Configurable I/O and, according to the rumour mill, several others have it on their development path. Invensys claims that its “Universal I/O” product doubles the I/O intensity (effectively halving the real estate and cabinets required) in a project. The company also indicates that indirect costs associated with control systems typically require an additional 20 per cent investment to the actual system value. Honeywell claims that using Configurable I/O results in up to a 33 per cent reduction in installation costs, in large part because of reductions in engineering hours, real estate and the associated incremental investment for ancillary items.
The Honeywell and Invensys systems both support discrete input, discrete output and Analog I/O with HART signals that are configured through system software. As a result, these systems are effectively hardware independent. The Invensys “I/A Series Intelligent Marshalling Solution” has eight individual isolated channels per card with support for pulse signals, as well as four signal types. Honeywell’s “Universal I/O” supports full redundancy with 32 channels per module. The third DCS option is Emerson’s CHARM (CHARacterization Module), a special terminal block supporting the four basic signal types with intrinsic safety, as well as thermocouple/millivolt inputs. With this option, you install a CHARM for each signal, up to 12 per base plate, to a maximum of 96 channels per carrier that is then wired back to the control system.
A number of non-DCS manufacturers, including WAGO, Advantech, Moxa, Pepperl+Fuchs, Stahl and Phoenix Contact, also make remote I/O products that are similar to CHARMs, though they will not integrate or be configurable directly by the DCS system to which they are connecting. These systems typically communicate by some form of Ethernet-based industrial protocol that will require mapping the parameters/signals to registers in the controller. The fieldbus organizations are also continuing to develop products and tools to make connection of remote I/O easier. The Fieldbus Foundation, with its F-ROM (Foundation for Remote Operations Management) project, is working to develop an I/O system that uses DD (Device Description) files to provide an integrated end-to-end solution as a single platform-independent environment. Through their relationship with ISA100, F-ROM will support a wired or wireless backhaul, though the present remote offerings more closely resemble traditional I/O cards of one card per signal type. Like HSE, on which F-ROM is based, the challenge is getting DCS suppliers to support the HSE protocol. Now that F-ROM has demonstrated HSE with remote I/O, a DCS supplier without Configurable I/O may work with another project participant to develop the appropriate “card” to be mounted in its backplane.
One constant about the automation industry is change, and though one of the fieldbus advantages appears to have been replicated with Configurable I/O, an all-digital system continues to have advantages, including less field cable, power over the wire, fewer terminations, and full bidirectional digital communications. Configurable I/O has the advantage of flexibility integrated into the control system while retaining the comfort of traditional wiring practices. Just like we have different buses for different applications, the same is likely to hold true for Configurable I/O systems.
This column originally appeared in the October 2013 issue of Manufacturing AUTOMATION.