How do you test and debug PLC programs before deploying them to the field?

Todos los software de programación de PLCs incorporan simuladores software para testear los programas. En mi experiencia, el problema radica en ser capaz de definir los escenarios de prueba. Lo voy ha explicar con un ejemplo simple un botón de marcha y un botón de paro de un motor. Cuando pulsas marcha arranca y cuando pulsas paro para. Pero que pasa si el botón de marcha se queda enganchado. Que depende de como este hecha la lógica volverá a arrancar. Se deben probar las condiciones de funcionamiento correcto y todos los errores plausibles que pueden producirse en un escenario real. Todo esto debería ser fácil de probar en cualquier software actual. Estas pruebas deberían realizarse con cualquier cambio, por peque?o y nimio que parezca.

In addition to all this, don't forget to design proper testing procedures during startup. There WILL be problems even if you thought you simulated everything well. Common problems may include valve actuators that hunt more than you expected, too much or too little hysteresis for a pressure switch, not considering what happens if an instrument goes in to a "trouble" state (such as losing echoes for a radar level gauge). Be ready for things like this with adjustments you can make in your software. You may need to insert some time delays for bouncing switches and the like. In short, you won't be able to simulate everything, so be prepared for I/O that doesn't do exactly what you expected.

To do a good process simulation is necessary understand very well the scope of work, interfaces with anothers disciplines, how instrumentation was selected, etc. After this, preparing a FAT documentation as reference considering a real situation of process, when applicable and possible.

I'm sort of laughing at ALL of this... 'testing the PLC' is far more than Input, Output, Results. Speaking as a former IFT(Integrated Functional Test) Engineer in lab environments at Rockwell's Landerhaven facility it's THE INTEGRATION that needs to be tested (Firmware acting on Hardware WHILE using Software to monitor 'the Nature of Behaviors'). Believe me when I tell you "Works as Intended" is NOT reality for Controls 'in the Real World' because it MAY be dysfunctional for "Works as Needed". Timing in the midst of Layers of Communication Strata alone is a nightmarish reality for those of us who grew up on Analog controls and direct wiring.

Many PLC manufacturers provide simulators or emulators that allow you to test your PLC program in a virtual environment. This helps you identify issues without the need for physical hardware. Simulators mimic the behavior of a real PLC and can be valuable for early-stage testing.

Emulation mode lets you iron out PLC software faults internally before releasing your code for formal testing. It's an important first step before peer reviews and external testing. It allows you to get an estimate of the PLC scan times to ensure the PLC hardware is compatible with your PLC program. In most cases, you won't have access to an HMI so end-to-end testing is not possible. But you can create operator screens in your PLC software application e.g. with Schneider Electric PLCs.

Emulation mode in PLC software allows you to run and debug your program on a computer, mimicking the actual PLC hardware. It uses real firmware and memory, offering a realistic testing environment. While providing accuracy, it requires external devices for I/O simulation and may have speed and memory limitations based on your computer's capabilities. Emulation mode is cost-effective, aids integration testing, and helps identify issues before deploying to physical PLC hardware.

Testing is a important phase befor software deployment to save time , efforts money and provide environment to field engineers. with just compiling and solving the warnings and key point we can already debug the software and make it more optimized to avoid deadlock and software malfunction situation in real environment. Then comes the simulation testing to test your hardware and code execution and last emulation to check the operation of process and optimize it without real environment. Though pre-defined test cases always help in the last one and you can already minimize the first part by using automated tools to generate software like UML or xml-based code generation.

maybe offline mode is better here to state. Before connecting to the actual PLC hardware, perform offline testing using software tools provided by the PLC programming environment. This allows you to review and debug the logic without affecting the physical system.

A emula??o seria importante em uma quest?o de abordar o funcionamento do hardware real do sistemas, criar assim um ambiente para se comportar de forma parecida ao ambiente real, gerar atraso nas resposta dos acionamento, inclus?o de ruídos dependendo da área de atua??o. Até uma quest?o de comunica??o e rede é interessante se estabelecer na emula??o se houver tempo hábil.

Debugging tools are essential for testing and debugging PLC programs, whether using simulation, emulation, or real hardware. These tools, integrated into PLC software, include breakpoints for pausing execution and inspecting values, watch windows for real-time variable monitoring, force tables for overriding values, and traces to analyze program history and events. These tools help track data changes, simulate scenarios, and analyze timing and logic, enabling efficient troubleshooting and program refinement.

Debugging functions helps narrow down the specific areas in your PLC program. It reduces the herculean task of manually searching for bugs and fixes. These tools are provided by the PLC manufacturers to analyze issues. In siemens for example, watch tables, Traces, cross referencing are useful debugging methods.

Debugging tools in PLC software, essential for testing and troubleshooting, facilitate program monitoring and modification. Features like breakpoints enable pausing execution to inspect variables and inputs. Watch windows display real-time variable values, while force tables allow overriding input/output values. Traces offer event sequence visualization. These tools aid in tracking data changes, simulating scenarios, and analyzing program logic and timing across simulation, emulation, or real PLC environments.

A Depura??o é essencial durante todo o processo de emula??o e simula??o, ferramentas que facilitam a visualiza??o a??o por a??o do programa ou exibi??o a cada ciclo de scan ajudam a validar se o comportamento do programa no ambiente virtual corresponde ao comportamento esperado no ambiente real.

Whether utilizing simulation software, emulation mode, or a physical PLC device, effective testing and debugging of PLC programs require dedicated debugging tools. These tools, integrated into your PLC software, facilitate real-time monitoring and modification of your program during execution. Key features include breakpoints, enabling you to pause execution to inspect variable values, inputs, outputs, and registers. Watch windows display selected variable values in real-time, while force tables allow overriding input, output, and register values. Traces provide a history of events, aiding in understanding program behavior over time. These tools are essential for tracking data changes,

Normally, code should be "self-explanatory". This means, that it should be written in a way, that comments are barely necessary. However, there are some specifics when it comes to PLCs. 1. Most PLCs reference some absolute addresses at some point. That is the case because at some point the signal has to come from an physical input. Because of this, symbolic names should be used that do NOT reiterate the absolute hardware addresses. 2. Always do some network comment. Depending on the PLC manufacturer, you might know this under a different name (i.e. rung). 3. Have a change history for the PLC program. Doesn't has to be something fancy like actual version control. Even a general table can do the job and is better than nothing in the end.

It reminds me of when I was just stepping into automation - staring at a PLC program with no comments. Those cryptic variables made no sense. ?? I learned the hard way - take time to explain your logic and variables! Your future self will thank you when making changes or troubleshooting late at night. Meaningful names and comments save headaches later. ?? Document that PLC program! Your coworkers and future self will appreciate it. Now, after 15+ years, I make sure to document any collaborative work. ?? It makes life easier and lets you enjoy vacations. ?? Thoughtful documentation upfront pays off long term. I can attest diligent commenting has saved me many headaches over the years! So don't forget to document your PLC program! ??

Effectively documenting and commenting your PLC program is a crucial best practice for testing and debugging. These written explanations and annotations enhance program clarity, making it easier to understand, maintain, and collaborate on. Clear, concise, and consistent documentation assists in identifying program purposes, logic, and errors, facilitating modifications and updates. At various levels – program, block, or line – provide overviews of objectives, inputs/outputs, parameters, and logic, ensuring comprehensive and accessible information for programmers and stakeholders.

During my professional career in PLC programming, I realized that documenting the software, commenting on the programming logic, using easy-to-understand language, and simple logic is not just a matter of organization, but an act of respect for the colleague who will need to make changes or perform maintenance on the machine.

?When documenting test results, include details of what didn’t work by describing failures, steps to reproduce, diagnostic data, and root cause analysis. ?Clearly document corrective actions and retesting results to enhance system reliability. ? Ensure to comment your code thoroughly and use clear, descriptive names for inputs and outputs to improve readability and ease of maintenance.

? Start by performing a complete I/O check. Verify all physical connections and labels, power up the system, and check the status indicators. ?Test digital and analogue inputs by simulating signals and ensure the PLC reads them correctly. For outputs, activate each point and confirm that connected devices respond as expected. ?Use real-time monitoring and debugging tools to step through the program and observe its behaviour.

A la puesta en marcha del PLC es conveniente ir con una plantilla preparada con todas las pruebas necesarias. Comenzando por el reconocimiento de se?ales y activación correcta de salidas. Probando las distintas maniobras. Y algo que normalmente por falta de tiempo no se contempla: Depurar el programa para las situaciones anómalas que no hemos definido en el proceso. Por ejemplo, si un motor debe pararse al llegar a un final de carrera... ?Qué pasa si ese final de carrera no funciona?

En mi experiencia, algo que también suma es crear interfaces HMI que facilite la visualización del estado de las variables. Muchas veces, cuando el proceso es grande, la lista de variables es extensa, por lo que depurar la lógica viendo estados de activación/desactivación, perjudica pues confunde en vez de ayudar. En ese sentido si elaboramos un "scada" simple (Que solo servirá para el comisionamiento) que pueda indicar los elementos de control animados, facilita a tener claro como evoluciona el código, de esta forma permite ubicar errores rápidamente, por ende depurar se hace más sencillo.

Creo que es fundamental crear un documento que permita registrar las pruebas que se realizan al sistema. Este documento debe ser completado primero en forma interna y luego junto al cliente, de manera de demostrar que el sistema funciona correctamente. Para crear este documento es una buena idea hacerse la pregunta: ?Que pasaría si...? Esto nos puede dar una buena idea de las condiciones que soporta nuestro sistema.

Starting from the hot loop check, it's very important to check that each software tag communicates with its assigned appropriate hardware tag. After doing a hot loop check, logic check plays a vital role. Checking of the tripping logic with actual operation of the field element is also important to check system healthiness. Soft tag communication with the third party system also needs to be checked and make sure all the tripping logic tag need to be hardwire to increase system reliability.

PLC developers have to get better at writing automed tests, and the more important process of test driven development (TDD). The vast majority of your tests of your PLC software should be the low-level unit tests, see "the testing pyramid". This will ensure you will get a good design of your PLC software. It will also ensure you will have a battery of regression tests that can be executed at any point in time. Further, the tests will act as documentation for any developer that will have to maintain and expand the code. All the tests cases will act as an acceptance criteria for your code. Only relying on manual testing, which unfortunately is the norm in industrial automation, is risky and mostly results in bad software architecture.

Testing is important, but... You can reduce it effectively with Libraries and version control. My systems are all based on a custom library that I developed for the company I work for. These control objects in the library go through a TDD (Test Driven Development) process, and then an Integration test with common objects that will it will interact with. Following this approach means that the low level testing for the object is reduced to zero when next implemented, as long as the version is controlled. Following this approach has dramatically reduced errors, testing requirements and has increased reliability and confidence in the software. But it all starts with test driven development

Though testing is crucial for PLC/SCADA ?? programs before commissioning. Use simulation software to emulate I/O and the industrial process. ?? Debug in emulation mode before deployment. Utilize debugging tools like breakpoints, watch windows, and variable tracing.?? Add clear comments and documentation for maintainability. ?? Validate safety circuits, process simulations, MES/ERP integration.?? Follow testing procedures and logs. ?? Consider OPC communications testing, hardware-in-the-loop, CI/CD pipelines. ?? Robust testing methodology ensures smooth site acceptance and avoids issues during qualification runs. ?

In my experience, testing your PLC, HMI/SCADA softwares should be done to reduce time spent during commissioning and implementation. A good test with many scenarios is effective.

Simulation across multiple disciplines in buildup to a plant go live has always beneficial, allowing engineers to get a real feel of the systems designed. However, simulation was limited to planning & feasibility tests until now. However, the capability of digital systems is expanding and now enables us to test the PLC code against the designed systems in the digital world. This is phase of validation is referred to as virtual commissioning, where most equipment, sensors, motors, drives can be modelled & parameterised. As virtual commissioning is becoming a main stream activity, OEMs are able to validate the PLC code almost completely before arriving onsite, with savings upto 30% to 40% of the onsite commissioning time.