Product category:
Smaller-Sized PLCs
News Release from: Omron Corp | Subject: CJ1 and CS1 PLCs
Edited by the Engineeringtalk Editorial
Team on 26 October 2004
PLCs speed through function block
processing
The latest range of programmable logic controllers from Omron features high-speed function block processing.
The latest range of programmable logic controllers from Omron features high-speed function block processing Programmable logic controllers have been in use in a wide range of automation tasks for over 30 years
This article was originally published on Engineeringtalk on 25 Oct 2005 at 8.00am (UK)
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During this time, considerable improvements have been achieved in their capacity, speed and functionality.
But all recent developments have primarily focused on improving the ease of use and integration of PLC technology in automation applications.
This covers the complete range from sensors to actuators and from field equipment to plant management systems.
In the early days, internal resources were scarce.
Programming in mnemonics and ladder diagram allowed very economical use of memory and processing power, at the expense of transparency, portability and maintainability.
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Omron has introduced a new version of its universal PLC programming software, adding powerful new features, while maintaining the ease of use for which the company's software is renowned.
With the advent of standardisation through the IEC61131 family of standards for PLCs, the need to unify PLC programming methods has grown.
Addressing should no longer be directly linked to vendor-specific hardware, and this should result in easy re-use of code.
Unfortunately, the additional processing power needed to handle the additional overhead could severely affect the performance of control systems.
As Omron's reputation in the field of PLCs has always been for high speed and reliability, such a compromise would not be acceptable.
The most important mechanism defined in IEC61131-3 to facilitate the re-use of code is the user-definable function block.
By separating the control process into logical, function-related units, blocks of control code can be made machine-independent, and therefore easily transportable.
In principle, user-defined function blocks may contain control code very similar to conventional PLC programs in any of the defined programming languages.
The main difference is that all data within the function block is symbolic and no longer directly linked to hardware or fixed memory allocations.
The control code defined in the function block can therefore be re-used within the same PLC task, shared between multiple tasks, or copied to other PLCs, without any change of the internal code.
With many competitors' PLCs, the invocation of a user-defined function block will cost significantly more processing time than the conventional way of programming.
Due to the required transfer of data, more advanced memory management techniques need to be employed in the internal software of the PLC.
And often, the use of these function blocks is an option requiring extra software to be purchased, or extra memory to be installed in the PLC hardware.
With the latest versions of the CJ1 and CS1 families of PLCs and CX-Programmer V5, Omron has now swept away these restrictions.
All CPUs now support user-defined function blocks as standard, with no extras required.
And most importantly, while keeping the same speed and reliability thanks to novel hardware architecture that relieves the firmware.
When using function blocks, the structure of each block is defined once.
This is the type definition, describing the input, output and internal state parameters, plus the algorithm in the function block body.
The body uses only symbolic variables to assure re-usability, and can consist of ladder diagram code (LD), or it may be written in IEC61131-3 compatible structured text (ST).
Whereas ladder code is better suited for sequential control and interlocking, ST is mostly used for data processing, complex calculations or decision branching (if-then-else).
A mix of LD and ST function blocks within the same program is allowed.
Each time a function block is used in a PLC program, an instance of the function block is created.
Input parameters are transferred to the instance, its body is executed, and the output parameters are transferred back to the PLC program.
This whole process is called invocation of the function block.
After the invocation, the internal state of the function block instance needs to be stored until the next time the instance is invoked.
With multiple instances of a function block type used in a PLC program, this will require more memory space and data management to assure correct re-entrance of the instance in the next control cycle.
In conventional PLCs, each invocation will delay normal program execution significantly.
All new CJ1 and CS1 CPUs (from Ver.3.0) contain a new version of Omron's own control code execution engine.
This ASIC, named MULCE (multilingual control engine), performs frequently used control instructions by hardware, without any load on the central processor.
Moreover, it will autonomously handle all memory accesses and instructions required for a function block invocation.
As a result, execution of function blocks is just as fast as normal ladder program execution.
The result is a no-compromise controller offering speed and ease of use.
The complete range of CJ1 and CS1 CPUs now have additional built-in memory to handle function blocks.
The built-in memory allows storage of the complete function block structures, enabling upload of the complete control code from the PLC, including function block variable definitions and comments.
The user program can be 100% restored from the PLC memory, without the need of optional memory cards.
This unique ability to upload the exact program and function block structures can be of vital importance when troubleshooting and performing maintenance on control systems in the field.
The new function block functionality in CJ1 and CS1 PLCs is an important step for the Omron's Smart Platform concept.
By using predefined and tested function blocks, the effort to integrate intelligent units or field devices into a control system will be significantly reduced.
Omron function blocks will provide program-less access to smart device functions such as online self-diagnostics, preventive maintenance statistics or self-tuning data.
A standard function block library is already available, supporting temperature controllers, vision systems, motion controllers and smart sensors.
An ever-increasing number of function blocks is freely available for registered CX-Programmer V5 users, and all are fully customisable.
With intelligence getting more and more distributed, system integration by simple and fast communication between devices is essential.
Omron's PLCs enable this with their smart function block architecture.
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