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PLCopen
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TC5 - Safety - introduction

PLCopen, together with its members and external safety related organizations, defined safety related aspects within the IEC 61131-3 development environments. With this, the safety aspects can be supported by a dedicated software tool, which is integrated into the software development tools. As such it combines the logic and motion application development with the related safety aspects. This combination helps developers to integrate safety related functionality into their systems, even from the beginning of the development cycle, while contributing to the understanding of safety aspects.

Basic requirements

The basic requirements for safety application for the machine builders are independent from the applicable safety standards:
Separation between safety and non-safety functionality
Deployment of applicable programming languages and language subsets
Deployment of validated software blocks
Usage of applicable programming guidelines
Usage of the common known error reducing measures for the life-cycle of the safety related software
 

Standardization – the way out

For users, these high demanding requirements should be controlled and reduced. This can be done via standardized solutions with which the normal functionalities can be easily implemented. Standardization in functionality and the integration and support from the software tools helps the programmers to integrate safety in their applications from the beginning, without inhibiting their functionality and performance, and without adding costs. This was exactly the target of the PLCopen Technical Committee 5 – Safety. With support from nearly all relevant safety control suppliers, software suppliers, and safety related organizations, they produced the first specification. Included in this specification is:

Representation of the software architecture
Definition of the programming languages
Presentation of safety related datatypes
Definition of language subsets
Definition of user levels for safe and fast programming
Programming guidelines
Error handling and diagnosis concept
Certification guidelines for the function blocks
The definition of a set of 20 safety related function blocks.
 

Overview of the applicable Function Blocks

Equivalent Antivalent
Mode Selector Emergency Stop
Safe Stop 1 Safe Stop 2
Safely Limited Speed Electro-Sensitive Protective Equipment
Safety Guard Monitoring Safety Guard Interlocking with Locking
Two-Hand Control Type II Two-Hand Control Type III
Sequential Muting Parallel Muting
Parallel Muting with 2 Sensors Safety Request
Testable Safety Sensors External Device Monitoring
Out Control Enable Switch

User Benefits

This complete approach provides the user with a harmonized view to the total application, safety and non-safety related application software within one environment. And with multiple implementations, this is also valid across platforms.
This means less educational efforts, and simpler transfer of knowledge and application software between different controls. Also, it tackles the ‘not-invented-here syndrome’, which often is a cause of errors and additional costs. By using tested functionality, and support in the programming environment, including language definition with subsets of functionality, one is able to create safety related application programs for easy commissioning.


Specifications

Part 1 - Concepts and Functions Blocks - is focused to the implementers of the safety functionalities. With this part 1 the safety aspects can be transferred to a software tool, which is integrated in     the software development.
Part 2 - User Guidelines - is focused to the users of the PLCopen functionalities and demonstrates the ease of use of the defined function blocks in real life applications.
Part 3 - Extensions to the Function Blocks - extends the scope of the specification and harmonizes the diagnostics interface for easier handling by the user.
Part 4 - Application specific FBs for Presses - contains a general overview of the implementation of safety around presses.

 

BGIA, the German certification institute for research and testing reviewed the PLCopen specification Part 1 and confirmed that it meets the relevant aspects of IEC 61508 and the related standards and can be used as a part of a specific safety requirement specification.

 

The German test & certification organization DGUV approved the PLCopen Specifications Part 3 and Part 4 as suitable basis to develop function blocks for safety applications for presses. As such the DGUV recommends that for safety applications for presses the function blocks are developed according to the PLCopen document and that their functionality is tested on a press.

 

 

 

 

 

 

 

 

 

 

 

 



 

 

 

Certification

For quick identification of compliant products, PLCopen has developed a logo for the Safety Specification:

 

In order to fulfill the requirements set, different levels of certification are applicable:
  1. Certification of the software tools, often part of the control supplier
  2. Certification / Conformity of the application at the user and/or machine builder
Ad 1: Certification of the software tool supplier

The development environment, including the safety related function blocks, as well as the underlying hardware, have to be certified by the relevant safety related bodies. In order to be able to be certified, certain rules, like described in IEC 61508 and related standards like IEC 61511, are applicable. The PLCopen specification provides a framework for this; however the overall requirements are beyond the scope of PLCopen, and have to be dealt with by external dedicated organizations.

Ad 2: Certification / Conformity of the application

Within an application, a certification includes the safety related software combined with the infrastructure, like sensors, switches and actuators, connection schemes, etc, like described in standards like IEC 62061. Certification or approvals for the application software are made easier, however the full application have to be dealt with by external dedicated organizations. The use of the PLCopen logo does not give any guarantee about any compliance or fulfillment. The use of the logo just refers to the inclusion of the ideas and guidelines as described in this document, within the relevant software environment, and the availability of this information in more detail on the relevant section of PLCopen website.