PLC Logics and HMI Screens for User Roles Management: A pratical approach to PLC authentication / authorization using IEC 61131 - 3 Ladder Logic (AUTOMATION RECIPES)
This booklet is the fifth of a series dedicated to automation recipes created with the PLC (Programmable Logic Controller) and HMI (Human Machine Interface) binomial. The series is aimed at an audience of readers with an elementary knowledge of PLC programming, eager to learn advanced solutions, extensively tested on real systems. In modern computer programming, generally oriented to the development of "object-oriented" software, the developer strives, as much as possible, to resort to so-called "Design Patterns", standard solutions for frequently recurring problems. A design pattern describes a problem, particularly recurring in a given context, and then provide the heart of the solution to this problem. It is therefore possible to successfully reuse this solution, thousands and thousands of times, with the certainty of using an efficient and well-tested solution. In the present series, which deals exclusively with development on PLC-HMI, the term "design pattern" has been replaced by the term "automation recipe" for an easier understanding by the non IT reader. This fifth notebook addresses the issue of authentication and authorization of the user; mandatory topic in every computer application project but very neglected in automation projects with PLC. From this point of view the innovative character of the contents and the uniqueness of the topics will surely be appreciated by the reader. In detail, the first section of this notebook, dedicated to the application domain, illustrates the problems related to the authentication and authorization of the user by means of appropriate login and password fields. It is then shown how not only the navigation of the HMI pages can be authorized or denied according to the user's access role, but also that some fields of the screens can be rendered not visible to the unauthorized user. The second section deals with the development of combined software for both PLC and HMI. The logics of the Login subroutine and the LOGIN password access screen as well as the main navigation MENU are explained. Finally, the third section shows the application of the concepts developed in a specific case of a waste water pumping plant. All the logics, published in the book, have been developed using the IEC61131-3 compliant Ladder language; therefore it is extremely easy to migrate them on almost all the PLCs of other manufacturers. The same applies to HMI screens whose graphic controls are very similar on the different equipment offered on the market. The reader who already has experience with other manufacturers' equipment can therefore continue to use what he knows best.