i have an application where we would like to have the ability to do programming changes on a PLC via a modem (Allen Bradley SLC 5/05, if it makes a difference). However, we don't have a telephone line available. Does anyone know of a manufacturer that makes a modem that functions using wireless (that is, cell phone) communications?
we have apply this system.
we use ip static to remote monitor ( we use leased line via- fiber optic and satelite, we think cheaper than via cellular phone. ) slc plc, for prgrammning and monitor the data, then logging data to our central server.
for remote terminal we use 1 pc server with linx gateway to acces plc from central server.
pc central we use rslogix500 , rs view and linx.
pc remote ( direct to plc ) use rslinx gateway. gateway addres of plc use address of remote pc.
why we use pc remote? because some times our technician visit the remote plc for check or maintain.
then we use pc remote to for temporary logging data, so our central server not work heavily with raw data from plc.
for all applicartion, land line or cellualar we think, best use static ip. because setting of linx more secure and safe if use static ip than diynamic.
the difficulty ( because i am not a satelite man ) when we 1st time to make route to plc remote from central server. ) best if you need advice from your line provider to connect from central in order to acces plc ip number.
the summary of our work to connect
1. make route from pc remote to plc. via comand com of windows xp
2. make route from pc remote to pc server( ask to satelite man, faster than try by oursef), idem
3. sett gateway of plc to ip pc remote. than
4. set all linx setting to connect each other.
5. get conected from you central to plc.
Just done this myself and so have gone through the headache.
There are two main types of connection, remote initiated and remote terminated. Remote initiated means the remote device makes contact with you, remote terminated is where you want to make contact with it. Remote initiated is the easiest from an IP address point of view, in the same way that your PC can have any address on a LAN that is connected via a router to the internet, the remote device can have any IP address. But you need remote terminated, this means that you will need to know and have access to the remote devices IP address.
Different wireless providers have different solutions or APIs to solve this problem. All of them route the connection from the remote device to an IP address on their private networks. Some then give you access to their private network so that you can reach the device, others map their internal IP address to an external IP address on the web. The internal IP address is more secure because script kiddies have no access. A fixed public facing IP address is more flexible and can be contacted from anywhere in the world but anyone can try to break in.
A further complication is part of your question of whether to have a fixed IP address. As mentioned above you need to know the remote devices IP address, so if the provider changes it all the time you would be sunk. However there is a solution, the wireless device knows its IP address and transmits it to a Dynamic DNS company who then let your system know what is the current IP address of the remote device. Of course they do charge for the service.
That headache has come back again. The answer to your question is that you need to know what the wireless provider can offer before you can decide what you need.
