2.1. Objective

Many applications require a quick reaction time via the distributed I/O. In SIMATIC, PROFIBUS DP is used for fast and efficient data exchange between distributed I/O and S7 stations. Typical configurations consist of one DP master with several DP slaves that are operated on the non-clocked PROFIBUS DP. Programming units (PU) or operator panels (OP) are also frequently used on the DP line.

In PC-based automation, a visualization is often used in the DP master in addition to the control job. This raises new questions.

One of the most important questions when designing such DP configurations concerns the "DP reaction time" to be expected:

• How long does it take until a distributed output reacts to a distributed input when
  • processing is performed via the process image and the cyclic OB1?
  • processing is performed via direct commands and the process alarm OB40?
• Which statistical fluctuations can occur?

Just as important are the questions regarding the performance of the HMI devices:

• Which update time (time of a signal change at the input until it is indicated) can be expected?
• How long does it take until the output is set after pressing the button (operating time)?
• Do these times also apply when visualizing with the DP master (PC-based)?

Furthermore, the mutual effects are also of interest:

• Which influence does communication via PROFIBUS DP have on the cycle time of the DP master?
• Which influence does an increased utilization of the DP master due to an additional load program have?
• Which effects does the simultaneous operation of programming unit and operator panel on the same DP line have?

To answer the questions listed above, the "Industry Automation" Division has performed extensive measurements with typical mono-master systems on the non-clocked PROFIBUS DP.

To conveniently access the measurement results, you can compose your desired configuration with the interactive user interface.