Currently, I am doing an upgrading project, which employed Profibus DP network consist numbers of Siemens S7/200,300 PLC, a HMI station monitors the building condition, retrieves data through an Applicom card, from which to exchange data with EM277 DP module.

We purchased two PCU1500PFB brand new cards and finished the design on software and Hardware redundancy. However, a crucial problem been found and the whole thing go to a halt.

A DP slave always needs to exchange data with the only master in this network to get the configuration and identify itself when power on. Things happened when power cycle the PLC, all the WO* registers contain PID setting will be overwritten to zero. Moreover, all those WO* are controlling the PID output to maintain the temperature and relative humidity in side the CleanRoom¡­¡­..

According to the Em277 spec, applicom will store output data form HMI and write cyclic to the PLC. If disconnect the profibus connector the V memory will still be kept. Looks like Applicom card wipes all data after recognizing the Slave.
I have contacted and ask the local Tech support staff to come and help, he left with no result.
Any help will be appreciated. Thanks

Li Wei Shi,
A-control.Pte.Ltd

 

Let me get the whole picture of the network because i had a problem like that.

The S7-200 with the Em 277 is tha slave and the Master the s7-300 is writing the data to it, And the HMI is also writing to the S7200?

 

Hi,

I have scores of these EM277 units in the field, once configured correctly, they're transparent and problem free.

You should check the special memory words within the S7-200 to confirm that the Host configuration is correct (referencing the expected V memory addresses) also remember that the Host configures the IO configuration as well, so ensure that your buffers are configured as you expect. Beyond that, v-memory as output will be read but not written to, v-memory as input will be written to but not read by the master.

To be sure, I keep the PROFIBUS buffers separate and access them once a cycle. This avoids background pass and consistency problems (which may not exist!!)

Regards

Marc Sinclair
--
http://www.germainesystems.co.uk

 

As we are only about to upgrade the HMI, PLCs will remain original, probably. People had considered such saturation many years ago, and already writen something to take card. But We could not bear the loss of our assumption.

V memory won't be overwritten until the DP slave module receives configuration message from master and enters the data exchange mode. During normal operation, as long as don't power cycle PLC, everything runs smoothly.

I suspect that when initialization of DP communication happens the Output Buffer inside PLC will be force to zero. Number of output & input Bytes are zero shown in the "DP Slave module information" before pluging into the network. If so, What else I can do....

 

Hi,

This sounds quite sensible, during configuration, the buffer should be cleared, it sounds like the s7-200 program doesn't take account of this. Try copying the data you want to share to the buffer area every scan, that way it's always fresh, and always there.

Marc Sinclair
--
http://www.germainesystems.co.uk

 

Well the problems i have when I do the Profibus network of s7-200 with HMI to connect to a master S7-300 the problems I have was:

1. The HMI write the values to the S7-200 and the S7-300 write the values as well when I began the DP network so the valuse start changing really fast and they remain in 0 all the time. To solve it I do a change value program in the S7-300 and S7-200 in the comunication network, befor I send the data and after.

2. The comunication V* was in the same part as some V of the program so you need to change the ofset in the hardware configuration of the EM277 in Step7.

 

The Tech-support of Applicom product finally acknowledged this issue & promised to feedback to us once received solution from their R&D team based in France...