Programming Help

Scads can be implicitly divided into a server part and a client part. Interrogation of field devices and data collection is done by the server (usually via PLC), from the server the clients take this data to their monitors. The notions of “server” and “client” part are conditional. In fact, the division is made by licenses for scada components, and the licensing policy of each manufacturer is different. Up to the division of: the number of processed signals from the field, protocol drivers, the number of workstations, the ability to create a web interface, mobile interface, and even whole pieces of functionality can be for some money. It is often easier to contact the vendor and provide the initial data on the project to help with the selection of licenses.

There are two modes of operation: development mode and runtime mode. These modes are not necessarily mutually exclusive: you can edit the project on a single workstation, the engineering one, fill it in and it will be updated on the user workstations. This is very important – to change the project without downtime and shutdowns, because the technological process can not be interrupted, and operators should always be able to control it. Scada creates graphical interfaces, configures data sources from field devices, it is responsible for user (operator, dispatcher, technologist) interaction with what is happening in production, as well as archiving all the necessary data in the database.

Archiving is one of the mandatory functions, it is very important to be able to “go back in time” to sort out the flight in case of something unforeseen or for global analysis in slow, long processes. For example, I was recently asked by geologists to unload a table of data on oil pressure at wells over the past year.

Periodically, scada puts all the collected data into a database. They can then be viewed in the form of graphs (we call them trends), and if necessary, if stipulated in the TOR for the APCS, it can be unloaded in the form of reports in Excel or something else. Archiving is done in different ways: in MS SQL, MS Access, in the same MS SQL, but according to its own cunning algorithm with additional archiving, and some even in their own binary database.

Programming Help

A special item in scads is informing the operator: current messages and alarms. They are also necessarily archived. In general, messages are divided into current and important (alarms). Current messages are hidden away, but the log of alarms is always displayed on the operator’s screen. Audio messages are attached to text alarms, so that somebody did not oversleep an emergency 🙂

SCADA market

The most common, in my opinion, are scads made by Invensys Wonderware, Iconics, Siemens, Indusoft, AdAstra, Emerson, Rockwell Automation.

I personally have worked with the Windows ones: Invensys Wonderware InTouch and more powerful System Platform, with Iconics Genesis32 – and with (yet?) little-known B&R APROL under SLES (technically, it is not quite a scada, but cooler – from under Aprol are programmed and the controllers themselves).

For search queries, such as SCADA, HMI, you can see examples of interfaces and mnemonic schemes.

Appearance and usability is, alas, in last place. And it concerns not only the rantime, but also the development. For development, every scad has at least default symbol libraries, from buttons and other controls to graphic images of pumps, pipes, valves, and containers. Here the clever SCADA-package developers (not to be confused with us, asushnikov – the developers of projects in these packages) could achieve a fundamental advantage over competitors, making thoughtful libraries, from which even the most distant from the design and usability engineer, despite the reluctance would make humane interfaces and mnemonic schemes. Unfortunately, this sphere now follows the same extensive development path that IT developed until recently – functionality buildup, adding more, higher, stronger, harder, better, stronger, and users are not thought of enough.

Middle level

The middle level is PLCs, programmable logic controllers. Here everything is simple enough, most often physically PLCs consist of separate modules. For programming, each PLC has its own development environment, sometimes it is combined with the environment to create SCADA.

The modules are as follows:
power supply unit;
digital inputs;
digital outputs;
analog inputs;
analog outputs;
temperature inputs;

PLC’s composition