Radio Links Between Plcs ?

[Guest Ken]

I recently came across an Allen-Bradley's Plc systems which has a module comes with an antena on it . I want to ask some questions : 1.What type of CPU allow for such radio communication between them ? 2.How is this link setting up ? What kind of the code we must write in program betwween master Plc and slave Plc ? 3.How reliable of radio link compares to cable link ? How much electromagnetic noise or object blocking ( like building wall ) interfere to it and how far it can reach ? Does anyone familiar with this or know any reading materials relate to this subject ? Thanks ,

[Chris Elston 78]

I dunno which one you got, but check out these companies listed here: http://www.mrplc.com/sites/displayrank.cgi?|57

[chrisbramall 1]

Hi as detailed in one of the other threads I have linked two SLC5/03 PLC's together using two external RDT radio modems acting as a DF1 node to node gateway using the msg command to read and write data. The link updates about once every two seconds at a baud rate of 19200. Is this any help ?

[Guest Ken]

Thank you for the Web site. One more question for Chris Bramall : Do you ever encounter any problem with it at all ? I mean , what happen to your datas when someone working with power tools close to it during transmitting or receiving datas. We use 2-ways radios to communicate to each other at our large plant where hundreds of machines running at the time and sometimes we can not communicate at all due to a lot of static noises , or sometimes we had strangers ' voices in our radios because someone outside the plant happened to use the same frequency with us in their radios. Tell me more about that?

[Ken Roach 194]

A module with an antenna on it sounds like a Data-Linc SRM-6000 mounted in the chassis. Those are terrific modems; they are 900 MHz "spread-spectrum" so it's difficult to interfere with them with just one broadcast frequency. They also have pretty good diagnostics, so you can program them to exclude the frequencies used by your 2-way radios, or frequencies that have a lot of junk on them from motion control or other electrically noisy processes. There's a lot to be said for proper antennas, too; I saw one of these installed at a steel mill where the master is outside the potline building and transmits *through* the corrugated steel walls to cranes running inside the building. That had a well-tuned antenna. I also saw one where the antenna was placed 1/4 wavelength away from a cinder-block wall. That effectively snuffed most of the transmission.

[chrisbramall 1]

We didn't have too many problems but keep a rolling check on the data stream using a time output transmitted from one PLC to the other and back again. If either PLC did not see a change for a set number of seconds the system was configured to shut the process down until the communications was reestablished. The radio system used was an RDT unit with a range of 10km but we were working at approx 0.5 km so we could dial the power level down a bit, and we could selected a free frequency. I havn't come accross the spread spectrum units but they sound pretty could from kens description.