From OpenSCADAWiki
Data sources are characterized by a large variety, which can be divided in three groups:
- Sources of "raw" data, providing the ADC code or levels of discrete signals, and also the sources which include simple processing. Typically, these are modules of distributed MODs or simpler industrial programmable logic controllers (PLCs).
- Powerful industrial PLCs, which have significant computing power and the possibility of formation of complex parameters with different structure.
- Local or related data sources. For example, the MOD as expansion cards, and also the data of the environment of hardware and software in which the system operates.