When it comes to exchanging data between the PC world and the automation world, there is no way around an OPC server. At least that is a widely held opinion. However, our experience with Siemens S7 controllers is quite different. We have successfully realised projects with OPC server and projects without. Sometimes the use of an OPC server is unavoidable then, this question does not arise. Most of the time, however, it is possible to do it without one.

Our experience has shown that data transfer can even be faster and more reliable without an OPC server. The prerequisite for this is a good implementation of the ISO-over-TCP protocol (Profinet) in the PC software. This is exactly what we have in our software. With the help of the Profinet interface, our software is able to read and write data blocks from a Siemens S7 PLC. Also the connection to several PLCs is not a problem.

The advantages of a direct Profinet connection are obvious: No complex OPC server configuration and no additional license costs. But not so obvious is the speed advantage of a direct Profinet connection.

The diagram on the right shows how fast this can be. We measured the speed with a S7-1200 CPU with data sets of different sizes. The data sets are read from a data block and written into an Excel file. The times here are well below 200ms per data set. It should be noted that a large part of the time is needed for writing into the Excel file. The pure data transmission via Profinet is much faster.

Writing speed of datasets into Excel with an S7-1200

The transmission time depends on many factors: PLC-CPU, program utilization, network, PC speed, etc. With a fast S7-1500 CPU and almost ideal conditions we were able to realize transmission times in the range of 1 ms. The S7-1200 used here for measurement is of course slower. There the pure transmission times are about 10 to 12 ms.

Especially when a lot of data has to be read or written, our software brings clear speed advantages. For example, if you use our Excel-PLC coupling to acquire machine data. This allows you to read a lot of data from the data blocks of one or more Siemens S7 CPUs in a short time.

Advantages of a direct Profinet connection

  • Faster data transmission

  • Lower costs (no OPC license required)

  • Less work for the PLC programmer

Further information and free trial download

PLCDataReader

SPSDataReader

PLCDataWriter

SPSDataWriter

PLCDataSuite

SPSDataSuite