Modern control systems much appreciate the graphical user interfaces. “A picture is worth a thousand words”, but it seems that the future of Human Machine Interfaces in automation is far beyond that.
As opposed to the SCADA term, a lightweight local user interface of a machine is sometimes referred to as the human-machine interface (HMI) – in this context it is an embedded part of the machine. SCADA, on the other hand, is an all in one software package that consists of tightly coupled components implementing functionality to operate a system as a whole. It is worth noting that in spite of application kind this interface is a place where an interaction between someone responsible for making a decision and something responsible for the decision execution occurs. This post address the question what are the consequences if this interface is used, for example, to start drilling by a CNC machine, in one case, or alternatively to start moving remotely say load of 200MW from one power plant to another one in other case. After all, in both cases the operation can be initiated by pressing a virtual “ACCEPT” button on a touch screen. However, is it a sufficient reason to call this interface as an HMI device in both cases, and what is more important, can we use the same or similar solutions in all circumstances to decrease development and deployment costs?
In any cases, while interacting with a machine or with a system finely we operate a process. To operate effectively we must fulfill the following requirements:
- Provide a representation of the process behavior and its current state – output interface;
- Provide sensors to allow entering the operator decision – input interface;
The vendors of modern solutions – that meet highly demanded customer expectation – for this purpose employ 3D graphic, touch screen, voice recognition, motion tracking and many others technologies. However, communication with the user is only one aspect that we must focus on. To recognize others we have to look under the cover.
Automated processes are dynamic and stateful, so the interface has to provide an informative context for decision making. To reach this goal the process behavior must be tracked all the time by processing its variables to optimally adjust the screen content and expose the most important elements in an instant of time. Once there are more and more process variables within the automation systems, one has to choose, how to organize the structure of control system and mappings with the visualization purposes. Each variable can be recognized as a set of attributes: value, quality, timestamp and meaning. First tree attributes can be simply expressed as simple (primitive) or complex numbers and bind to the graphic on the screen in a generic way. The fourth (meaning) attribute is usually assumed that it does not change over the time, and therefore the interface behavior and appearance is designed (hard-coded) to express it in a communicative way. For example, we can distinguish a selected part of the screen to allow operator communicate with a chromatograph analyzer in a pharmacy automation process.
Unfortunately, this design time approach is often too rigid to seamlessly adapt for example exchange of the device by a new one from another vendor. Furthermore, hard-coded approach is useless when we must deal with multifunction devices that use pluggable components and variety of accessories. To avoid this unnecessary design cost and avoid proprietary solutions we need a next generation solution that can be called “Semantic HMI”. Semantic HMI is an approach that relays on discovering the meaning of process variables using the meta-data provided by the plant floor measurement and control devices, like analyzer, PLC, DCS, etc. In this approach the meta-data must be provided as a context for the real-time process data and processed simultaneously by a smart enough semantic HMI.
OPC Unified Architecture technology meets all the requirements, because:
- It is a platform neutral standard allowing easy embedded implementation
- It is designed to support complex data types and object models.
- It is designed to achieve high speed data transfers using efficient binary protocols.
- It has broad industry support beyond just process automation and is being used in support of other industry standards such as S95, S88, EDDL, MIMOSA, OAGiS.
Connection between HMI, as the decision entrance device, and process control device, as the decision execution device, may engage many technologies (e.g. RS232 serial bus located inside the box containing both, Internet, wireless connection, etc …). Unfortunately, vulnerability of the communication medium is only one measure of the security issues severity. Directly related decision cost and its consequence makes together another measure that must scale the required security robustness. In other words, without authentication of the transferred data, data sources and users we cannot expect and rely on the responsibility. Even in the completely shielded control room of a nuclear power plant, at the end of the day we must know who is responsible for pressing the virtual “ACCEPT” button if any problems occur. On the other hand, can you imagine a message on the screen saying “you must login to continue…” in a really critical situation in places like that.
There are more and more modern solutions of HMIs: advanced graphics, with high resolutions and touch screen, high IPs for front panels, faster CPUs, integration with modern operating systems, etc. However, they must offer much more to be used as a decision entrance device in applications like process control of municipal-wide heat distribution network located in the city of Lodz Poland (750k citizens), supplied from three plants with total thermal output power of 2560MW producing hot water distributed using ~800km of pipes interconnected by ~8000 nodes. In application like that, the most important features are openness to be seamlessly pluggable, visualization flexibility to expose process data in the context of process metadata, and appropriate security precaution to provide selective availability to control functions. It seems that using new standards, like OPC UA and new technologies, mentioned above could cause synergy effect leading to reusable on-the-shelf products withstanding even most demanded requirements.
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- Read full story: Control systems, HMI change management, security