Zlinx Radio Modems

[Noely 0]

Hi, Has anyone ever used ZLinx radio modems with allen bradley plc's. I want to connect a panelview 300 to a slc 5/03 processor via DF1 communications using wireless technology, or has anyone got any recomendations as to how to go about it.

[Rod_Hackney 2]

There are several radio suppliers that are in the Allen Bradley partner program that supply radio modems. Both licensed and spread spectrum license free models. I would look at ABs website for referenced manufacturers. I have worked with Esteem radios in the past and they are an AB partner.

[paulengr 44]

I've had extremely good luck with Aerocomm modems. The price is very good. They work very well for DF-1 traffic. There are limitations. You can't try to do any sort of "multiplexing" with them. The radios handle it but they are protocol-unaware so they do it very badly. You can also create an Ethernet-like interface (the radios have a small Lantronix board mounted in them according to a tech at Aerocomm) but don't expect to get some sort of "free" Ethernet out of it, especially since it's not PCCC-ethernet. I do have a setup where I did the multiplexing. I put in a PLC-09 arbitrator and put in 3 separate pairs of radios on it. Everything works fine. The range is pretty good. They are currently penetrating lots of metal walls, through a concrete block wall, and past a vat of RF noise...err, liquid metal. I went for them for a second reason...wavelength. I know that everyone keeps talking incessantly about 802.11 and "standards" but they fail to realize that the 802.11 standards are horrendous in terms of the typical industrial plant because they lack decent penetration. Speed of light is 2.98x10^8 meters/second. At 900 MHz, that works out to 900 x 10^6 cycles/second. Doing the division, you get 0.33 meters (wavelength). Below about 10% of the wavelength, for the most part, conductive objects are effectively "transparent" from an RF point of view. So anything thinner than about 3 cm is almost radio-transparent. That's why AM radio works so much better inside a building than FM in many cases. Once the object starts to get thicker than that, from an RF point of view, things get messy really quickly and you get dead spots as a result (actually, diffraction patterns). At 2.4 GHz, the wavelength is now just 12.4 centimeters so objects have to be 1 cm or less to be "transparent". At 5 GHz, essentially everything conductive becomes a reflector. This 10% rule isn't hard and fast, but it at least gives you something to shoot for. So although you get more bandwidth with 2.4 GHz or higher, from an industrial perspective, speed is often not a serious issue. It's nice to be able to simply ignore the building structure since 900 MHz nicely passes through almost everything. Once you are at 2.4 GHz or higher, steel structures become a serious penetration problem and optical and radio "line of sight" usually mean the same thing. Aerocomm sells a nice frequency hopping radio that does just that. They are extremely simple to use. They have a DB-9 port. Depending on the model you get either RS-485 or RS-232 (although you can't use DH485 with them). You can configure them with the free software to several different channels, turn on DES encryption, etc. They are very simple to use. One additional trick. The "master" always has the link light on. The slave actually indicates when it has a solid link. So put the "slave" where you intend to do your troubleshooting.