Implementer (Machine Manufacturer, Programmers)

<< Click to Display Table of Contents >>

Navigation:  FAQs >

Implementer (Machine Manufacturer, Programmers)

FAQ Machine Manufacturers, Programmers


Selmo Engineering


Are software, PLC and HMI exchanged during retrofits?   


Software always, PLC and HMI not necessarily. In retrofit projects, the technical status of the installed hardware must be assessed. If, for example, a TwinCat 3 controller with the corresponding panel is installed, it is not necessary to replace the controller and HMI. However, if it is an older TwinCat 2 controller, Selmo recommends replacing the hardware, as support for these controller types expires in 2024.



Why replace functioning software?  


A functioning software is rarely a software that is easy to maintain and operate. Especially older machines that have been producing for years and are to be integrated into a digital production system pose a challenge. The machines are usually not digitally visible, or only to a limited extent. Selmo enables bit-precise diagnosis of the machine and thus reduces downtimes in the event of a fault. This cannot be guaranteed by manually programmed software.    



What information must be known about the existing machine in order to be able to model it?     


The sequence of the machine must be known, even if only in the form of videos and photos. This information is already sufficient to model the process in the logic layer. Ideally, the electrical diagram should be available for modelling in the grid layer "hardware level". If not, then the majority can be modelled via an IO setup. Controls and information from subsystems are collected on site.



How can Selmo expand systems?


Selmo also offers the option of modelling and generating individual, independent step chains. For example, if a conveyor belt of a transport system is extended by a turning unit, the sequence for this unit can be modelled. The generated step chain is then integrated into the inventory software.



Can the software also be changed manually later? 


Yes, the software can also be changed manually. However, this is not expedient, as any benefit of the Selmo method is lost.  



Can safety-relevant PLCs be generated?


No. Safety programmes must be created with the manufacturer-specific software. Selmo guarantees the highest functional stability and safety, but not in terms of personal safety.  



Why is it advantageous or necessary to always monitor ALL bit patterns of a step chain? 


This provides the guarantee that the system is in the exact expected state and that no unnoticed deviations occur. This requires a sufficient amount of sensors in the system to be able to decisively monitor every state. In this way, the maximum functionally stable software can be guaranteed.



What does the Selmo method do for my engineering?


An engineering boost. For you, your partners, your customers. Common, modern system modelling sometimes comes up against limits because production systems are becoming more and more complex. Many interfaces offer many potential sources of error. The Selmo method is different: it starts directly with the requirements description. The process is the focus, serves as a common view of the system and is simultaneously the model from which the plant software is generated. Because interfaces are eliminated, engineering time is significantly reduced and the scope for interpretation is minimised. Selmo thus leads to a great increase in efficiency and quality.





What does the free engineering tool Selmostudio do?


Creating step chains and PLC software becomes faster and easier with the innovative modelling tool. Selmostudio reduces the complexity of PLC programming to the essentials: What should the machine do and how is it mapped? Once the programmer and process expert have understood the simple principles of Selmo, Selmostudio is an engineering turbo.



How much faster is Selmo than manual programming?


As a skilled programmer, you can programme a simple step chain with a few cylinders in around three to four hours - if you know the process flow and how a step chain works. With Selmo, you only need to model the sequences and the assemblies and link them via the BitControl. Then the quick generation and import into the PLC takes place. The HMI is automatically generated from the programming code. An HMI developer would need several hours for this. If existing processes are required on different PLCs, then a generic model of the process is ideal. With Selmostudio and the generator for different PLCs, Selmo supports machine builders who today must program different software for the same mechanics. 



What are the main functions of Selmostudio?


Selmostudio implements the Selmo standard. It is a modelling tool, PLC generator and HMI generator in one. With the Modeller function, you create step chains (finite automata) and digitally document your machine system. It uses discrete state modelling for this purpose. Transition-related sequence programming is no longer necessary. The integrated generator creates the sequence logic software and the user interface fully automatically. With Selmo, unlike other solutions, you can process and display every possible bit pattern of a step chain.



What are the main advantages of Selmostudio?


It is free to download, demos and modelling examples included. With Selmostudio, inputs and outputs are modelled as zones. The modelled sequence with all steps and zones is generated directly as standardised, error-free and hardware-independent PLC code in accordance with IEC 61131-3. Programmers can import the code in future into any type of controller that complies with this international standard. Selmostudio generates not only the syntactically error-free PLC code from the sequence description but also the HMI. The operator is provided with a uniform, system-independent operating concept: a Selmo system always provides information on what is happening, what needs to be done and what is missing in the event of a malfunction. Selmo minimises downtimes for your customers and maximises plant availability. This increases customer satisfaction. You get more focus on your successful tasks.


What are the benefits of Selmo modelling? 


Up to now, process and machine sequences in graphical form have usually served as the basis for programming the sequence. The description is doubly complex: First graphically informal, to create a common understanding of the process, and then formally in PLC code for implementation. Selmostudio creates PLC and HMI code directly from the process description. Only sensors and actuators have to be assigned to the individual steps in the grid layer. This means that the process engineer-programmer interface disappears completely; the double effort is eliminated. 


Does generation also help me with software checks? 

Unit and integration tests are conventionally carried out to check software for errors. Standard syntax checks detect many manually caused "typos". Logical or syntactically correct typing errors, however, must be searched for by unit tests at great expense. To find any deviations from the graphically described sequence, they have to be restarted after each software change. Selmostudio takes over this translation work for you and generates syntactically correct, error-free software. As with any other programming or modelling method, the process steps must of course be correctly formulated in advance.



How can I imagine the generation of the HMI?

Selmostudio generates not only the PLC code from the model but also the HMI. Inputs and outputs are modelled as zones. You can define which zones require an HMI button for operation. The modelled sequence with all steps and zones is generated directly and the diagnosis is derived from it. The operator or your customer receives a uniform, plant-independent operating concept. For maintenance, there is no longer a system standstill without an error message. Each step chain reports the error and indicates what is missing to continue. In this way, Selmostudio minimises downtimes and maximises your customers' plant availability.


What is the benefit of the Selmo software structure that is always the same?

To make the software maintainable, large plant operators specify software standards or structures. These specifications must be implemented at great expense and consistently adhered to. After all, acceptance is the goal. PLC code generation with Selmostudio, on the other hand, automates compliance with the standard: The code always has the same structure, regardless of function. The Selmo standard makes the code easy to understand because it is always structured in the same way - whether for an assembly line or a woodworking machine.


What do my customers and I gain from a hardware-independent software design according to IEC 61131-3? 

Often, the same plants for different target markets have to be delivered with different controllers because many plant operators rely on a single controller. The software must be rewritten or manually adapted for each required control system. Selmostudio, on the other hand, generates the PLC code according to IEC 61131-3, so programmers can import the code into any type of controller that meets this international standard.


Is there support that I can contact?


Yes - but we assume general PLC programming knowledge. The Selmo support team is available to you by e-mail support (to or via our contact form (

 from 9:00 to 15:00.  We will be happy to make you an individual offer for workshops, training and consulting. Selmo licence partners receive free training and ongoing support.


I want to give user feedback. Where do I turn?


We are a start-up that makes our tool available to you at a low cost. Our innovation is constantly being developed. Therefore, we look forward to your feedback. They don't always have to be positive. On the contrary: we learn from the toughest critics. Write to us via our contact form ( about what you would like to see in the next versions of Selmo. 


Are Selmo training materials available?



We offer individual training online and offline - at your site or directly at ours. Training is provided in the Selmo way of thinking about processes. Tutorials with application examples are being planned and will be published step by step in our help centre( Use our Selmo demo there to get a first impression of the Selmo benefits. Further functions and practical examples will follow. We want to react to the market and its needs - and not the other way round.


What basic knowledge do I need to model and generate step chains with Selmostudio?


Basically, Selmo is easy to use. Even process engineers with little PLC knowledge can use it to model simple step chains and generate them with a click. The challenge is to change the way of thinking from sequential logic based on transition conditions to state modelling. If the process has been thought through logically and precisely, the greatest effort has already been made with simple step chains. For larger plants or retrofit projects, the expertise of Selmo system engineers and licensees is required. The implementation of the PLC program requires experience with PLC development environments. Our support and scheduled tutorials enable you to implement simple applications yourself.



Do I necessarily have to generate with Selmostudio or can I just model and then programme manually?


You can just as well just model and programme yourself. Our tool is an aid for digital project planning and for quickly generated PLC code for step chains. Automatically implement step chains always in the same structure, without deviations due to individual programming. Use our tool as you need it. It can be used and tested free of charge.


How do I get the exact sequence logic of the machine??


The sequence logic is derived from the informal process description and is based on the description of the machine sequence. It is simple step-by-step thinking without the distraction of driver details. As a result, with Selmo we achieve a common understanding for all involved, from the very first moment.


How can step chains be executed in parallel?? 



Which signals are to be monitored and how are they defined?


On which controllers does Selmostudio already run with the integrated code generator?


The Selmo model itself is hardware-independent. At present, Selmostudio supports all controllers based on the TwinCAT 3 system from Beckhoff. Our development experts are working on supporting other controllers. Status January 2021: Integration in the CODESYS software platform is about to breakthrough. Work is underway on further CODESYS-based PLCs. Because Siemens does not support the import of PLCOpen, Siemens will be specially integrated on-demand. Selmo strives for platform independence for its customers and licence partners and prefers open systems as a first step. 



Is the generated PLC code readable for the PLC programmer?


Except for the core blocks, which are in a compiled library, the generated PLC code is readable. You receive generally understandable machine software. The PRG block is a structure that is easy to understand. It is integrated via the block call and the individual inputs and outputs are attached to the block. The module functions like a switching mechanism and can be compared to an IC. When the inputs are connected, the logic reacts with the outputs and display information. In principle, we rely on diagnostics at the HMI instead of an online search in the program code.



Do changes always have to be made with the code generator?


No, changes do not necessarily have to be made in the code generator. However, we at Selmo recommend it, because any change to the generated PLC code can endanger the system integrity.



Is it possible to read back code - for example, because of manual changes?


No, reading the back code is not possible and not intended. Changes to the logic should always be made through the process, via the model and generator.



How do I get to Selmostudio and the Selmo demos?



You can register for Selmostudio without obligation and free of charge in our download area, download 3D demos and test Selmo in practice:




Do I pay for generating or for modelling?


Modelling can always be tested free of charge, including the generation function. You can test the system for a short time based on your step chain. Even during the test phase, you benefit from all the functions of Selmo. The step chains are generated in a PLCOpen XML file that is simply imported into the PLC. You do not pay until you are convinced that the step chain can run. Then you can apply for a license key ( The offer for your step chain will be sent to you. You only pay once you have accepted it.



How much does a step chain cost?


You pay for the performance of the generator based on the number of steps and assemblies in a step chain. A quotation for this will be sent to you when you apply for the licence key. An online calculator for calculating step chains is planned.



How do I get the step chain running for an unlimited time?


Via a licence key, which you can either request yourself in the "Selmostudio" tool - or via our website: 

1. you have downloaded the free Selmostudio, modelled it and generated the PLC code.

2. you have transferred the PLC code to the target system.

3. there you can read out the request ID. You need this to be able to use your PLC code generated by Selmo for an unlimited period. 4.

Fill out the form with all the required information and send it to us. 5.

You will receive an offer from us and, if accepted, an invoice. The amount depends on the number of sequences, steps and zones to be licensed.



Do I have to pay for the step chain each time it is generated?


No. The calculation is based on the number of steps and zones. You always pay only the difference to the amount already paid.

Example 1: Sequence costs € 599 - you extend the sequence (step chain) accordingly - new sequence costs = € 700 - you pay € 201 to use the new sequence.

Example 2: Sequence cost € 599 - you change the order of the steps in the sequence and the name of the zones = € 599 - you pay € 0 and can use the newly generated sequence immediately.