Measuring the impact of vertical integration on response times in ethernet fieldbuses

The introduction of Ethernet and Internet technologies in the fieldbuses of automation systems widely facilitates vertical integration. Control functions can coexist more easily with higher level functions such as supervision, production reporting or maintenance. But what does the response time of the control function become when architecture components -e.g. controllers, remote input-output modules or fieldbuses -are requested in parallel by other functions? In this paper, we focus on switched Ethernet-based fieldbuses using Modbus TCP/IP. The evaluation of the impact of vertical integration on the response time of control functions is obtained from a series of measurements on a real system. A great number of response times were measured with a specific automated equipment that we developed. Three types of load on the control architecture are studied: traffic on fieldbuses, requests on controllers and requests on remote input-output modules. The analysis of the measurement results shows which level of vertical integration can be reasonably allowed, taking into account the required response times.