Modbus RTU comm between Sentron PAC3100 and 1756-L73 AB CPU

Hi to everyone, this is my first thread in this forum, I hope you can understand my english... I'm from Argentina
I have a problem! I have a PLC project with a 1756_L73 CPU from allen Bradley, and I need to read variables from an energy analyzer SIEMENS SENTRON PAC3100 (7km3133-0ba00-3aa0) via MODBUS RTU, can anyone send me an example? it seems that my CPU doesn't have native modbus RTU port.
Tanks in advance!!

Welcome to the Forum !

You are correct; the 1756-L73 does not have a native Modbus RTU port. In fact, it has no serial port at all.

If the Siemens meter has only a Modbus RTU serial port, then you need to select a network to Modbus converter first.

There are quite a few EtherNet/IP to Modbus RTU bridge and converter devices. I strongly prefer the HMS Fieldbus "Anybus Communicator".

I cannot tell for certain if the Siemens meter has RS-232 serial port wiring, or if it is RS-485, or something else. That is one of the things you should also try to figure out.

I looked at a quick spec sheet for the Sentron and it appears to be RS-485.

There are several ways to get the data you need. As Ken as stated you will need to add something to the system to talk Modbus to the Analyzer. I have used the Red Lion DataStation Plus to do the Protocol conversion between a AB Plc and a Modbus device ($1,500 US). If you project needs a HMI in it you can also use a Red Lion HMI as it has the same protocol conversion function as the DataStation Plus ($800 on up depending on the size). Both of these solutions are very easy to configure and I have had great luck with the service life of the Red Lion products I have used in the past.

If you want a solution that plugs into the Chassis of your PLC then Prosoft makes several different Modbus Communication cards that work very well. They can be expensive (around $3,000 US) and are more complicated to use than other solutions. If you have a Point I/O System attached to your PLC, Prosoft has a card that will work with the Point I/O and is much more reasonably priced ($1,500 US). It only has Serial Communications but should work for your application.

Any more questions come on back,

You may use an AB Micro850PLC with 2080-SERIALISOL Plug-ins as a gateway.

Micro850PLC with 2080-SERIALISOL support Modbus RTU (RS232 and RS485)

MSG instruction can be used to communicate between Micro850PLC and 1756-L73.

And more important, Micro850PLC is quit cheap actually.

We have an Ethernet IP to Modbus Gateway.
http://www.icpdas-usa.com/gw_7472.html