Mitsubishi Electric is expanding its MELSEC FX3 series of PLCs with the FX3G, a compact controller for mechanical handling and plant engineering automation, offering 128 I/O (expandable to 256 I/O with a serial network), a powerful CPU, extensive memory and easy configuration through clip-on application modules. The company describes this new development as "customised control at a micro level."
Like all of Mitsubishi's third-generation controller series, the FX3 features advanced new technologies, including a second system expansion bus to the left-hand side of the CPU (central processor unit). Of major importance to many plant engineers and business owners - and in line with Mitsubishi's design policy with regard to legacy systems - it offers full migration capability and compatibility with the existing MELSEC FX series, so can retrofitted to existing control systems very easily.
The FX series is claimed to be the world's most successful line of compact controllers, with over nine million units sold over the last 30 years. Mitsubishi says that the original FX caused a sensation, as it led to the demise of the individual hard-wired relay as the base unit of control system engineering, creating new opportunities for control and automation of production plant.
Replacing the popular FX1N, the new FX3G is said to be resetting the cost-performance expectation, with a larger program memory, faster instruction execution, additional programming instructions and improved functions and expansion options. Particular advances have been made in communication and positioning functions, as well as seamless integration with other control devices and networking options.
In keeping with Mitsubishi's policy of maximum usability, the FX3G is based on the same space-saving technology concept as the more powerful FX3U and FX3UC, which are designed for high-level and demanding automation tasks. All the necessary components – including power supply unit, processor, memory and I/O – are integrated directly in the ready-to-use controller units.
Performance is claimed to be class-leading, with 0.21us processing per logical instruction cycle and sufficient memory for 32,000 program steps. It can therefore handle significant automation tasks. If users so wish, they can also take full advantage of structured programming techniques as per IEC 61131-3. Compared to the original FX1N, of course, this is remarkable performance that would previously have been available only through larger modular PLC systems.
In addition to the standard system bus for up to eight expansion, special function and network modules, the new controller also has a second bus system as per the larger FX3U series PLC. Up to four additional modules can be connected to this adapter bus, namely two interface modules (RS-232 or RS-485) and two analogue adapters - including a new temperature data acquisition module for Pt1000 and Ni1000 elements. This ADP bus makes the FX3G extremely flexible for a compact PLC.
The new adapter bus modules were developed specifically for the FX3 family, with modern technology that make them very compact. They can be integrated without additional programming and can be addressed directly with special data registers. In addition to reducing the number of program steps needed, this also saves engineering time and, therefore, money. Additional expansion slots are also available on the front of the unit, where up to two expansion boards can be inserted to add serial communications interfaces (RS-232, RS-422 or RS-485) and analogue functions.
Users can program the FX3G using the GX Developer or GX IEC Developer programming software package. This supports the IEC 61131-3 standard and program development with 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, making both programming and system configuration fast and simple.
The FX3G is offered in 14, 24, 40 and 60 I/O versions. Power supply is 100-240V AC for international deployment, with a 24V DC version to follow. 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 open fieldbus networks.
A display module that plugs into the front panel of the base unit provides quick access to information. Important controller data can be displayed and edited with the help of four function keys. A two-level password protection system with separate sets of access permissions for users and developers ensures that only authorised personnel have access to the program.
With communications and networking becoming ever-more important, the FX3G supports CC-Link, Profibus, DeviceNet, ASi, OPC, Freqrol, 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.
Each FX3G can act as either a slave or master on the CC-Link network. The ability to become a CC-Link master means that the FX3G can integrate to the Mitsubishi CC-Link Safety Relay, which manages basic safety functions such as emergency stops, light curtains and other safety devices, and gives users the added benefit of networked safety diagnostics back at the FX3G PLC.
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 - such as the Mitsubishi D700 - with dedicated instructions to make programming quick and easy. This enables speed and motion control tasks to be fully integrated, at low cost, with other control functions.
In summary the new MELSEC FX3G controller is economical for standard mechanical handling and plant engineering applications. It is a platform for building customised lower and mid-range automation control systems, and can be seamlessly integrated with the larger iQ Automation Platform series.