I/O Modules

Input/output systems find more use with PLCs; Ethernet and wireless are among top 5 means of communications. Respondents expect to buy more than in 2004.

I/O modules are applied most often as a slot in a PLC system or as distributed I/O systems; slot PLC connections saw the largest growth. Top five connecting communications are Ethernet, 4-20 mA, Modbus RS-485, DeviceNet, and wireless protocols. And, overall spending in the next 12 months will equal or top this year’s spending for a whopping 94% of respondents to a recent Control Engineering subscriber-survey.

To better understand subscribers’ I/O-modules’ applications and needs, Control Engineering worked with Reed Corporate Research on surveys for February 2006 and, previously, for December 2004. Mix of respondents differs, as do responses for the two surveys.

Among February 2006 study respondents—those specifying, recommending, and/or buying I/O modules—74% do so for in-plant requirements, and 46% buy for OEM needs. December 2004 saw 81% doing so for in-plant requirements, while 41% bought for OEM needs.

In 2006, some 37% of respondents primarily use I/O devices for both continuous and batch processing, while 16% cite continuous processing only; 28% discrete products, 13% utility services, 2% batch only, and 4% other. In 2004, some 45% of respondents primarily used I/O modules for continuous and batch processing, while 23% cited continuous processing only; 16% discrete products, 7% utility services, 5% batch only, and 4% other.

Types of modules

In 2006, discrete and analog input and discrete output represent the top tier of I/O modules used (over 90%) and will continue to represent the top tier of those used in the coming year.

In 2004, analog input, discrete input, network interface, discrete output, and analog output represented the top tier of I/O modules used (over 90%) and also are expected to remain the most used.

Endpoints of highest use for various modules (about 95%) and lowest use (about 50%) remained about the same as in 2004 and 2006. Within the high and low, few shifted more than 10 percentage points. PID went from 86% in 2004 to 74% in 2006.

In 2004, loop control went from 79% in 2004 to 68% in 2006. Blocks with network connections and blocks with on-board intelligence increased slightly from 2004 to 2006.

Applications for I/O modules

In 2006, 81% respondents apply I/O modules within PLC systems; 59% slot in PLC; 51% distributed I/O systems; 46% DIN-rail mounted from PLC control supplier; 35% PC-based systems; 25% DCS systems; 22% DIN-rail mounted from supplier different from controller; 20% network gateway; 10% programmable automation controllers (PACs); 14% single point; 9% IP67 block style; 7% IP67 modular style; and 2% other.

Largest changes in 2006 from 2004 were 12 percentage points more for slot in PLCs in 2006; 9 percentage points less for PC-based systems. Temper that decrease, though, with introduction of PACs, a new choice in the 2006 survey, which may account for the decline (PACs include PC logic with PLC-like ruggedness).

Some newer I/O technologies allow application flexibility, as any points to be used as input or output, suggests Thomas Trombley, Rockwell Automation Armor-Block I/O product manager, easing configuration to suit any control application.

Communications methods

In 2004 and 2006, Ethernet and 4-20 mA dominate current and future communications, both over 70%. Next closest was DeviceNet use at 59% in 2004; 43% in 2006.

The 2006 survey added questions on wireless, Ethernet, and other protocols. In 2006, networks used, highest to lowest, are Ethernet, 4-20 mA, Modbus RS-485, DeviceNet, wireless protocols, ControlNet, other proprietary, Profibus-DP, HART, CANopen, other, FOUNDATION fieldbus, Interbus, LonWorks, Optomux, and Seriplex.

Helge Hornis, intelligent systems manager, Pepperl+Fuchs (P+F), would add safety networks to the list, which he sees used significantly, especially in factory automation.

Robert Bristow, product manager for Honeywell, observes a “significant increase in the use of FOUNDATION fieldbus for process signals. Lately, significant portions of some jobs use that protocol, Bristow says, a trend he expects to continue.

Ethernet protocols, wireless

Among those using Ethernet protocols with I/O modules, highest to lowest, are TCP/IP, EtherNet/IP, Modbus/TCP, UDP/IP, FOUNDATION fieldbus HSE, Profinet, SERCOS III, Ethernet-Powerlink, EtherCat, other, and OptoMMP. Among leading protocols, TCP/IP at 80% and EtherNet/IP at 78%, were significantly ahead of Modbus/ TCP 38% and UDP/IP 28%.

Opto 22 suggests that Ethernet is far and away the feature/technology/communications medium of greatest interest. They have developed boards to swap with 20-year old I/O systems to make them Ethernet enabled, for easier information transfer to business applications. Opto 22 calls Ethernet the prevailing plant-floor communications technology. Senior application engineer for Opto 22, Tom Edwards, says, “Right now, Ethernet accounts for about 50% of the product we sell. By this time next year, we wouldn’t be surprised if that figure grew by 10% to 20%.”

Many reasons for Ethernet preferences, according to Bill Black, controllers product manager, GE Fanuc Automation, include ease of installation, hardware cost (off-the shelf switches and hubs), and familiarity with the technology.

That doesn’t mean everything is located at the point of measurement or actuation, Black cautions. “Despite the wide range of granular I/O [modules] designed to allow the user to distribute control, the trend is still to maintain half of the I/O connections in the control cabinet.... even though there has been a flood of DIN I/O modules, it is still expensive on a per point basis, and networking is still perceived as complex,” Black says.

Jeff Payne, product manager, PLC, I/O & PC controls, AutomationDirect, says communications is “possibly the greatest change in the PLC market over the past five years,” revolutionizing how PLCs are programmed and relay data with other PLCs and with PCs for HMI, SCADA, or DCS applications. “Communications consistently ranks in the top three decision-making characteristics of PLC and I/O products. While serial communications are still very popular, reliable, and inexpensive, Ethernet is fast becoming the communications medium of choice,” Payne says, because of network speed, ease of wiring, and availability of off-the-shelf networking components like switches and hubs.

Top six wireless protocols (used or plan to use) are 802.11 (any mention) 17%, Ethernet (any mention) 8%, Bluetooth 5%, proprietary 5%, WiFi (unspecified) 5%, and ZigBee 5%. Six others were mentioned. Indecision leads for use of wireless with I/O modules at 28% for “don’t know/haven’t decided/evaluating,” followed closely by 27% for other.

Purchasing

Among 2006 respondents, an average of 155 I/O modules were purchased during the past 12 months. Average spending per respondent on I/O modules in the past year was $111,737.

Hornis, P+F, says process automation use has influenced these purchasing trends. “A large number of factory automation applications use considerably less than the quoted 155 modules. Secondly, the average purchase price ($720) is very high,” he suggests, influenced by process automation responses.

Purchases of I/O modules will increase in the next 12 months among 47% of 2006 respondents; 47% expect to purchase about the same. Only 6% predict a lower demand. Slightly less expected an increase in I/O module purchase in 2004 at 43% in the next 12 months; 53% then expected to purchase about the same. Only 4% predicted a lower demand.

End-users increasingly want an “OEM to define the system, hand it to them, and guarantee the performance,” says Joe Benedetto, senior product manager, Schneider Electric. Also, “increasingly we see that end-users don’t need to buy the PLC’s bigger, more expensive I/O system. So if they only need 50 or 100 I/O points in one location, they buy distributed I/O because it is less costly.” A lot of distributed I/O modules are being used with PLCs because it costs less than larger I/O systems and requires less panel space, Benedetto says.

Leading features among those purchasing in 2006 were technical support, availability of stock, communication capabilities, and ease of use. Network capabilities rounded out the top five and cost was just below that (see graphic).

Responses to I/O module product features show the critical nature of support, Black, GE Fanuc, says. “Users demand easy installation, commission and trouble-shooting, and support.” Support rates highest, suggests Benedetto of Schneider Electric, since “a lot of end-users don’t have the inhouse technical support staff they once had, so they rely on manufacturers to provide that support. Capability to support a product is just as important as the performance of that product, in many cases.” Stock availability is important because “downtime is horribly expensive.... tens of thousands of dollars per minute, depending on the application. But panel control builders and other OEMs don’t want to keep an inventory because it costs money unnecessarily. OEMs expect manufacturers to have products available immediately.”