Dear all,
I have carried out measurements of delays in MPI and Profibus networks. CPU315-2DP is connected to CPU314 via MPI and CPU315-2DP is connected to Simoreg6RA70 via Profibus DP.
In MPI network I sent one byte from input memory of CPU314 to data block in CPU315-2DP and one bit is connected to output memory of this PLC. My probes measure the time between setting of input bit in CPU314 and setting of corresponding output bit in CPU315-2DP.
Then, I sent PPO3 to Simoreg and some bit is connected to digital output. My probes measure the time between setting of output bit in CPU315-2DP and setting logic '1' on digital output of Simoreg.
In both networks these delays depend on transmission speed but in both networks for constant speed I got different values. In MPI network, for tr. speed = 187.5 Kbit/s I got values from 29 to 69 ms. For tr. speed = 19.2Kbit/s I got values from 122 to 256ms.
In Profibus, for tr.speed = 12 Mbit/s I got from 4 to 8ms and from 43 to 71 for 9.6Kbit/s.
My problem is explanation of these results. I know both PLCs have their own cycle and each time CPU315 gets message in different instants of its cycle but why these results differs so much?
Best regards,
gumis
I have carried out measurements of delays in MPI and Profibus networks. CPU315-2DP is connected to CPU314 via MPI and CPU315-2DP is connected to Simoreg6RA70 via Profibus DP.
In MPI network I sent one byte from input memory of CPU314 to data block in CPU315-2DP and one bit is connected to output memory of this PLC. My probes measure the time between setting of input bit in CPU314 and setting of corresponding output bit in CPU315-2DP.
Then, I sent PPO3 to Simoreg and some bit is connected to digital output. My probes measure the time between setting of output bit in CPU315-2DP and setting logic '1' on digital output of Simoreg.
In both networks these delays depend on transmission speed but in both networks for constant speed I got different values. In MPI network, for tr. speed = 187.5 Kbit/s I got values from 29 to 69 ms. For tr. speed = 19.2Kbit/s I got values from 122 to 256ms.
In Profibus, for tr.speed = 12 Mbit/s I got from 4 to 8ms and from 43 to 71 for 9.6Kbit/s.
My problem is explanation of these results. I know both PLCs have their own cycle and each time CPU315 gets message in different instants of its cycle but why these results differs so much?
Best regards,
gumis
