Hi there,

I want to command a PLC controlled plant system remotely with the help of an SMS using GSM modem.

The user should be able to control the start/stop of the plant pumps as well as verify the status of them via a set of pre-programmed commands through SMS.

Can anyone please help me out in this regard??

 

If you work with SIEMENS S7-200, there are 2 ways for receiving SMS with a modem GSM:

1. Push-style: configure the modem to tell the PLC when a SMS is just received.
2. Pull-style: configure the modem to store the SMS and then the PLC asks the modemm for incoming SMS.

The second option is clearly more robust, because you will not have unexpecting comunications from the modem in the freeport comunication.
The configuration for this is AT+CNMI=0,0,0,0.

Then your PLC must ask periodically for new SMS. The AT command for this is AT+CMGR=1 (inbox 1). You will get the SMS in the V memory and then you can analyze it.

You will need however expert programming.
If you want to save time and gain robustness and flexibility, there is a library for STEP7-MicroWIN that solves the problem, Nubitek_SMS_Manager.
Have a look at:
http://www.nubitek.com/section02/pr01-sms_mgr.htm

You can download and test it for free.

Here you can also have a look at visual examples of use, like 'Communication in distributed installations':
http://www.nubitek.com/section03/examples.htm

Hope this helps!

Regards

J.C.