A Client is a computer program or a device that, within the framework of the Client-server model requests data, services, or resources from a server. This communication principle is one of the fundamental architectures of modern IT, automation, and measurement systems and enables the structured exchange of information within a network.
The client initiates communication by actively sending requests to a server. The server processes these requests and provides the requested data or functions. Although communication occurs in both directions, the exchange of data is controlled by the client. The client decides when information is requested, transmitted, or updated.
In measurement and automation technology, clients often retrieve measurement values, status information, or diagnostic data from devices and systems. For example, visualization software acting as a client can access a measurement data server to display current process values or analyze historical measurement data. Similarly, SCADA systems, control systems, or analysis applications can retrieve data from distributed measurement data acquisition systems.
Many industrial communication protocols are based on the client-server principle. These include, among others, OPC UA, Modbus TCP, MQTT with corresponding broker architectures, as well as various web and database services. In these applications, the client sends specific requests to the server and receives the desired information in response.
A practical example from the field of measurement technology is connecting a measurement data acquisition system to analysis software. The software acts as a client and retrieves measurement values from the server either cyclically or on an event-driven basis. This allows process data to be monitored, analyzed, and documented without the server itself having to actively send data.
The client-server model enables a clear division of tasks, centralized data storage, and flexible system scaling. As a result, the client is a central component of modern network and automation structures and has become an indispensable part of industrial measurement and monitoring systems.