Data acquisition systems (DAS) are the basis for building monitoring tools that enable supervision of local and remote systems. Unfortunately, DASs are commonly based on proprietary technologies. The data format usually depends on the industrial process, the fieldbus characteristics or the development platform. Currently, there are many standards of DASs, but none of them offer a well-accepted Application Programming Interface (API). However, all of them comply with the same conceptual model. Understanding this model allows for the significant improvement of the design of a specific DAS. In this paper, we propose a conceptual model of a generic DAS. This model gives researchers an abstraction of DASs and a quasi-formal specification of a generic DAS. It also enables developers to compare the existing standards and/or to propose a new open standard.