Siemens Scale Modbus Comms?

[speakerman 4]

Hello everyone; We have five Siemens BW500 Milltronics scales running totalizing programs, and would like to move their data into an Allen Bradley 1756 controller. The BW500 supports the Modbus RTU protocol, and we were considering that as an option. Is there anyone who has achieved this and can let us know of any barriers, challenges to overcome, or critical configuration parameters to make this work? It seems simple enough, but the 32-bit architecture of the 1756 controllers did create some unexpected complications with the Yaskawa drives we just installed, so I want to make sure we can achieve this before pulling wires and committing resources to the path. The milltronics units have 4-20mA analog outputs as well, so we could send the running rate to the PLC and write a program to totalize based on that. It would be very easy to wire up, and take a bit of programming to calibrate, but in the end it could not be as accurate as a direct reading through Modbus. If anyone can shed some light on this, please let me know. Happy programming, speakerman.

[Michael Lloyd 85]

Prosoft sells a couple of different Modbus cards that work pretty well. I would check them out MVI-56E Modbus Master / Slave MVI56E-MCMR Enhanced Modbus Master/Slave Communication Module (for use in a remote rack) The also have a Modbus TCP card that works really well.

[speakerman 4]

Thanks Michael; These are obviously going to work great with the AB, matching the 32 bit tag format, which was my only niggling concern. I'm sure the MODBUS side will be bullet proof. If we go with the Modbus, I have a feeling this will be the way. Happy programming, speakerman.

[Michael Lloyd 85]

The ProSoft cards can get and store floating point data (I don't usually use that functionality) or it can store floating point as 2 integers (default). Since everyone's idea of how data should be packaged seems to be different (though there is some standardization) I like the 2 integer method. Ive seen the need for word swapping, byte swapping words, and even word swapping byte swapped words. All of these can be addressed with a little coding in the PLC (look up the Bit Field Distribute (BTD) instruction.)