Combo I/O modules simplify system design

Reduce the panel space and cost of the central PLC you’re using by distributing I/O closer to the process.

FOR INDUSTRIAL machine configurations that are spread out over a factory floor—sometimes in different rooms—the control system designer is faced with additional cost and space requirements that can involve another PLC and accompanying I/O.

Many machine builders want to reduce the panel space and cost of the central PLC they’re using. Their PLC performs mostly monitoring, some control, and the link to the operator interface (OI). They would consider downsizing their PLC to a controller populated with only network interface cards or moving to a single integrated OI/Controller. This would eliminate the cost/space of the rack, low-density I/O cards typically found inside the rack, and overall panel size needed to house the instrumentation. With either approach, they could distribute I/O closer to the process in smaller junction boxes near the sensor zones.

This is the solution Acromag claims to offer with its Ethernet BusWorks I/O products, the newest of which is the 95xEN line of combination modules. The 95xEN modules include four analog inputs, two analog outputs, and six discrete I/O channels.

“What’s really new in our Combo Modules is the mix of the I/O, the design of the discrete input/output interfaces, and the availability of three Ethernet Communication options,” says Don Lupo, Acromag’s director of marketing & sales for process products.

The combo modules allow controls engineers to place a DIN-rail mounted, 1-in. wide package in a remote location. “They don’t have to deal with adding another PLC, controller or complex bus-coupled I/O solution,” says Lupo. “They now have the ability to grab one to four continuous or discrete process parameters, send information back to a controller over the network, and write to the analog and discrete outputs on the same module for control, shutdown, alarming or retransmission.”

The new modules supply six channels of discrete inputs or outputs in any mix or combination. “The technique involves populating all six DIO channels with circuitry for both sensing and high-side switching of 5-36 VDC logic signals,” says Lupo. “It’s known as built-in ‘loop-back’ monitoring. With this design, all channels remain inputs unless written, in which case, that channel becomes a sourcing output. For controls engineers it means when they turn a discrete output channel on or off, they can then read it back through a discrete input register tied to the same channel for validation. No extra wiring or looping back to another channel to verify the integrity of their outputs is required.”

Ethernet communication options for Modbus TCP/IP, Ethernet IP and Acromag’s new Ethernet i2o technology mean interoperability with major brand PLCs, controllers, recorders, PCs with HMI software packages, and embedded PC applications using VB, VC++ and .Net.

Performance specifications include 10/100Mbps communications, -25 to 70° C operation, three-way isolation, surge protection, high-accuracy/low-drift, field calibration registers for analogs, and approvals for CE and UL/cUL listing for Class I, Division 2 locations.

Lupo says Acromag’s Ethernet i2o technology allows two 95xEN modules to update each other automatically without a controller. Communication takes place over any Ethernet link, and no special software is needed as each module has built-in web-pages. Updates between modules are based on time and change of state. “For failsafe systems, output channels can be configured to ‘hold last value’ or fail to a pre-defined state in the event of communications, power or signal wiring loss,” adds Lupo.

With i2o, for the small cost and time of configuring a couple of Ethernet I/O modules, machine control system developers have the option to eliminate or minimize the expense of pulling wires. Lupo says an example would be the quick and simple addition of adding I/O modules to a system for switching applications, process stops, shutdowns, annunciation or data-acquisition/recording purposes.

The 95xEN products offer machine builders another advantage, claims Lupo. “Since they are simple, combo analog/digital I/O products, they can be viewed as devices that help Ethernet-enable any system,” he says. “By adding the module to the machine, users can Ethernet-access any 4-20 mA or discrete signal directly through their own Ethernet link or HMI system. In many cases, it’s simpler and easier to connect to analog/discrete signals than through digital protocol conversion devices on the network. And, since Acromag’s Ethernet products support up to 10 sockets each, up to 10 different users can view the I/O device at the same time.”

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