What should be considered when choosing flash memory cards for control systems?
- Automation
- 19.1.2024
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Depending on customer requirements, various 3rd party components such as exchangeable industrial flash memory cards from different manufacturers are also integrated into control systems. In contrast to conventional and cheaper end-consumer microSD memory cards that can be found in countless everyday electronic devices, industrial microSD flash memory cards are used in modern industrial automation. For example, in control systems, which are an important component of holistic automation solutions. Data and / or the operating system are stored on microSD cards on a very fast flash memory. As no moving parts are required to store the data - unlike HDD hard disks - microSD memory cards are more robust, more reliable and less prone to errors. So these memory cards should always work in modern control units without any problems, regardless of the manufacturer, right? Not quite, because the devil is often in the detail.
How to make the right choice of industrial flash memory cards?
During testing different combinations of flash memory cards in controllers for our customers, engineers at KEBA often discover that a card with a certain capacity works perfectly, while other capacities from the same manufacturer and model may not work properly and data may be corrupted. But why is that? Do state-of-the-art control systems in automation technology have a design or open system architecture with replaceable and non-soldered flash memory cards that could cause errors? Is it perhaps only due to the different properties and batches?
A precise analysis and definition of the customer's requirements and intended use forms the basis for selecting the right type of flash memory.
Flash memory types in comparison: SLC, MLC, TLC, QLC or pSLC?
Different types of industrial flash memory types (SLC; MLC, TLC, QLC, 3D-TLC, pSLC) naturally also have different properties and functionalities (e.g. service life, robustness for harsh industrial environments, speed, storage capacity, hard power-off stability, etc.) - and therefore also have corresponding price differences. A single-level cell flash (SLC) consists of one bit per cell, a multi-level cell flash (MLC) refers to two bits per cell, a triple-level cell flash (TLC) has three bits per cell and a quad-level cell flash (QLC) has four bits per cell. KEBA usually recommends SLC or pSLC (good price/performance ratio) cards in the control systems. MLC or 3D TLC memory types can also be installed at the customer's request. pSLC or pseudo SLC cards are based on MLC or 3D TLC technology. Instead of 2 or 3 bits, only 1 bit is programmed per cell, which increases the service life (program/erase cycles (P/E)) by a factor of more than ten. For this reason, the capacity is naturally reduced.
The more bits a flash array (storage infrastructure of flash memories) can accommodate in a cell, the smaller the flash array and the cheaper the memory module. The more bits per cell, the fewer program/erase cycles (P/E) the flash cell can cope with, which in turn makes it more susceptible to faults. If several bits are placed per cell and addressed with a cache flash memory controller, very high speeds can be achieved, but this also increases power consumption during reading and writing. The built-in flash controller and the firmware also play a decisive role. Manufacturers of industrial flash solutions can customize the firmware according to customer requirements and use it to solve problems. A precise analysis and definition of the customer's requirements and intended use forms the basis for selecting the right type of flash memory and the corresponding controller. This has a decisive influence on the required capacity, service life, speed and susceptibility to faults.
When choosing an industrial flash memory card, there are a number of basic points to consider:
- What is the minimum storage capacity required for the intended use?
- Which operating system is in use? (e.g. Linux or Windows)
- Is a database running on it? (if yes, then the memory card must be able to handle more write cycles)
- Requirements for the robustness of the memory card? (e.g: Resistance to damage or data loss in the event of a "hard switch-off")
- Required service life of the memory card? (by means of reference or test operation under typical production conditions, an extrapolation of the expected service life can be created by simulation)
Testing and optimization of flash memory cards in KEBA's automation solutions
During the development and implementation of holistic automation solutions for our customers, KEBA thoroughly tests all aspects of software and hardware components. Of course, this also applies in particular to our KeControl control systems with the industrial flash memory cards selected for and together with the customer. We check all the details about the processor and if we find evidence of an error in the processor implementation in the so-called errata document (correction directory), we let the memory card manufacturer take a look at it or even provide them with a whole assembly group for testing. Undocumented behavior of the processor during communication with the memory card has already been discovered several times. If this case occurs, we receive a firmware update or a new model of the memory card, test it thoroughly and then confirm that it meets our requirements. So we ensure that controllers, as part of our Kemro X automation solution, function flawlessly and, just like our other modular hardware and software components (e.g. controls, HMI, motors, I/O modules, engineering tools, servo controllers.....), are constantly being developed further.
At KEBA, we are working daily on new technologies and solutions to drive forward the seamless interaction and integration of different hardware and software components from different manufacturers and to take the openness of our Kemro X automation platform to the next level.
