New microPLC doubles speed, I/O

13 July 2009

Mitsubishi Electric has expanded its MELSEC FX3 series of microPLCs with the FX3G, a compact unit with 128 I/O that can be expanded to 256 I/O with the CC-Link Remote I/O network. It has a more powerful CPU, and easy add-on configuration through clip-on application modules.

Mitsubishi FX3G
Mitsubishi FX3G

Mitsubishi says the FX3 is among its third generation of controllers, and as such features advanced new technologies, including a second system expansion bus. It offers full migration and compatibility with the existing MELSEC FX series, so it can simply be ‘dropped’ into existing control systems.

The FX series may well be, as Mitsubishi claims, the world’s most successful line of compact controllers, with over nine million units sold over the last 30 years.

The new model replaces the FX1N. It has a larger program memory (32,000 program steps instead of 8,000), faster instruction execution (0.21 microseconds processing per logical instruction cycle, as opposed to 0.55 microseconds in the FX1N), 120 additional programming instructions and improved functions and expansion options.

Particular advances have been made in communication and positioning functions, the seamless integration of other control devices and networking options. The previous FX1N came in I/O sizes of 14, 24, 40, and 60 I/O models that were expandable up to 128 I/O. The FX3G comes in the same basic sizes, expandable to 128 I/O with expansion modules and up to 256 I/O with CC-Link.

Its 0.21 microseconds processing per logical instruction cycle and 32,000 program step memory enables it to handle significantly larger automation tasks and opens up the possibility, if the user desires, to fully utilise structured programming techniques to IEC 61131-3. Contrasted with the FX1N, this is a considerable performance advance which would have been available only through larger modular system solutions.

The new controller is programmed with the GX Developer or GX IEC Developer programming software package. This supports the IEC 61131-3 standard and program development with the function block, ladder diagram, instruction list, structured text and sequential function chart languages. The programming instruction set includes both basic instructions and over 120 dedicated application instructions. The previous FX1N supported three languages, MELSEC Instruction List, Ladder Diagram, and Stepladder.

I/O and other expansion options
The FX3G comes in 14, 24, 40 and 60 I/O versions. The power supply is 100-240V AC for international deployment, with a 24V DC version to follow for specialist deployments. All output types are available in digital relay and transistor versions, and all base units can be expanded to up to a total of 128 I/O with additional modules and up to 256 I/O via CC-Link networking.

A display module that plugs into the front panel of the base unit provides quick information. Important controller data can be displayed and edited with the help of four function keys. A two-level keyword protection system with separate sets of access permissions for users and developers ensures that only authorised personnel have access to the controller program.

With communications and networking becoming ever-more important, the FX3G supports Profibus, CC-Link, Ethernet, and CANopen, plus data communications via up to three serial interfaces.

A USB port and an RS-422 port come integrated in the front panel. Other connections can be implemented with interface modules.

FX3G can adopt either a slave or master status on the CC-Link network. The ability to become a CC-Link master means that it can integrate to the Mitsubishi CC-Link Safety Relay which manages basic safety functions like emergency stop, light curtains and other safety devices and gives the user the added benefit of networked safety diagnostics back at the FX3G PLC.

Second bus system: the “Adapter Bus”
In addition to the standard system bus for up to eight expansion, special function and network modules, (shown on the right side of the CPU in the photograph), the new controller also has a second bus system like its bigger brother the FX3U. These slimmer modules are shown on the left side of the CPU in the photo. They carry the marking “ADP.”

On the left side, up to four additional modules—two interface modules (RS-232 or RS-485) and two analogue adapters, including a new temperature data acquisition module for Pt1000 and Ni1000 elements—can be connected to this secondary “adapter bus.”

These new “Adapter Bus” modules can be integrated without additional programming and can be addressed directly with special data registers.

For positioning, the new PLC has six high-speed counters supporting frequencies of up to 60kHz. There are also pulse outputs for frequencies of up to 100kHz for controlling up to three independent stepping or servo motors. Direct connection is also available for up to eight variable speed drives with dedicated instructions to make programming quick and easy. This allows speed and motion control tasks to be fully integrated, at low cost, with other control functions.

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