Wireless Ethernet and Modbus/Ethernet

  • Thread starter Jody Gallant CET
  • Start date
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Thread Starter

Jody Gallant CET

We are planning on building a high speed wireless ethernet system in our local area. We currently build and service the control stations in the City (small city) and would like to make it so these stations can be on the same backbone. Is it possible, with a Sixnet RS-232/Ethernet converter, or something similar to reliably put all the stations onto the network? They are all Modbus RTU at this point and the master stations use a variety of communications types. (ie from Dialup to leased lines) Any thoughts? Ideas? Thanks Jody Gallant CET
 
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Raymond van der Tas

When putting your control systems on the LAN (ethernet) you will need to consider if your devices (controllers, plc's, etc) really do support multi-master access. You may find that some of your devices only tolerate a single-master at a time. This limitation may require to restructure your design. A good idea may be to place a blind-node (pc-box) close to your device(s). This blind-node will run an operating system like Windows9x, NT, 2000. If you then also equip this blind-node with an OPC Server you can reach the data accross the LAN with your favorite SCADA/HMI OPC Clients. Any OPC Server is capable of exposing its data to multiple OPC Clients simulatneously, thus providing multi-master access. In case your LAN is configured in a multi-domain, or in case you also want add internet access as well, you may find that Microsoft DCOM configuration becomes too complex or too limited. For those cases you can install ICONICS DataWorX32 v6.1 on your client computer(s). DataWorX32 is an OPC Client/Server capable of reaching remote OPC Servers either through plain DCOM or through a TCP/IP communication channel. Your favorite SCADA/HMI can then reach the remote OPC Servers through DataWorX32. In case you want to use GENESIS32 SCADA/HMI software you will not need the DataWorX32 module. Additional info www.iconics.com Raymond van der Tas
 
I know that Data-Linc offers advanced radio modem technologies for both Modbus and ethernet (Modbus/TCP/IP). They have been a leader in the industry for a long time, and their products are very cost effective.
 
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Richard Theron

Hi Jody How many wireless stations (nodes) would you be putting on the network? Are all the RS-232 devices Modbus RTU? What wireless system would you be thinking of? I presume that the master station is Modbus RTU as well. I have done a similar application before using UHF with 10 nodes and four RS-232 devices on each node. Worked very well. Regards Richard Theron FieldServer Technologies 1991 Tarob Court, Milpitas, CA, 95035, USA Phone: 408-262 2299 ex 125 Fax: 408-262 9042 www.fieldserver.com
 
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Jody Gallant

> Hi Jody > > How many wireless stations (nodes) would you be putting on the network? We have not gone so far as to get a fixed # of stations yet. Could be upwards of 30 Scada Sites, plus some other stuff. (see below) > Are all the RS-232 devices Modbus RTU? Most likely. > What wireless system would you be thinking of? We are looking at Wi-LAN. Our initial plan, is to build a single high speed network down the river valley. (all sites being in the valley makes it somewhat easier) The backbone will be 12Mbps using 4 wireless bridges configured point to point(two legs). At each of the sites, there will be another wireless modem (probably 4.5Mbps) configured as a multipoint master. Each lift station/pumphouse or control station will have a 4.5Mbps bridge configured as a multipoint slave. These will all be throttled back to 19,000kbps or so. The reason for all of the bandwidth is to help offset the costs with another project. There are currently no high speed WAN solutions in the area. (at least not economical, as even a T1 connection is >$1000/mth) We can sell the rest of the bandwidth to a few of the companies on the river who need high speed connections between their buildings in different sections of the valley. Also, the city is looking for a solution to connect all of its municipal buildings. (planning comission is using the sneakernet to bring autocad the 10kms from engineering to City hall) My point being, the water/wastewater is not enough justification to spend that much on a backbone, but if a single universal protocol (ie TCP/IP) could be used the system costs could be split up making it worth while. > I presume that the master station is Modbus RTU as well. > Yes, there will actually be several master stations, but being a single network, they could share the data. > I have done a similar application before using UHF with 10 nodes and > four RS-232 devices on each node. Worked very well. > > Regards > > Richard Theron > FieldServer Technologies > 1991 Tarob Court, Milpitas, CA, 95035, USA > Phone: 408-262 2299 ex 125 > Fax: 408-262 9042 > www.fieldserver.com Thanks for all of your help with this. Do you think what I am proposing is possible, or will sharing the bandwidth cause timing problems? Keep in mind, nothing is controlled remotely. All of the logic is at each site, only settings are changed remotely, and monitoring is done. Any Ideas/Comments? Thanks again Jody Gallant CET Shadcomm Ltd.
 
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Jody Gallant

Agreed. I have looked at these options as well. But considering the cost factor it doesn't really make sense. <$2000CDN for a 4.5Mbps Ethernet modem, or >$3000US for something well below 1Meg. I realize I don't need all the bandwidth, but a single system could be built rather then a bunch of them for different purposes. Jody Gallant CET Shadcomm Ltd.
 
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Paul Horvath

hi jody,

it sounds like you have a solid plan in place to justify the installation of a wireless high speed (10 mbs) network. Your potential customers for sharing the backbone may demand more of your system than you can provide however.

we have used data-linc products, but as fas as i know, they haven't offered a proven TCP/IP wireless connection yet. Most of there devices a simply a copper replacement medium and do not adhere to any IEEE standards.

i have come across two systems that work well.

The first is Grayhills EZ-Com IP Router. This is and industrial modem, however, it is only 2 Meg throughput and it does not comply with IEEE 802.11 or IEEE 802.11.B. It is capabale of going 30 miles using the appropriate antennaes and 60 miles (claimed) using a repeater.

The second is by BreezeCom as distributed by Black Box. This is an IEEE 802.11 (hopping, not dispersed, more important that you hop since you may have "customers") device and can go 30 miles with approriate antennaes and amplifiers. however, the throughput is 3 Mbps but you can overlap the cells to achieve 15Mbps throughput. This device is less expensive than the data links and we are currently using it in industrial applications. The device also provides load sharing so you can "promise" your customers reliable connections.

As far as using Modbus RTU over TCP/IP, there is a published protocol for "wrapping" modbus/TCP and a RTU packet. This is an industry standard and is published for public information.

i think someone had already mentioned putting a pc local which would perform your RTU conversion to OPC. This also is a solid solution. Once you have a number of OPC Servers installed talking to all of your RTUs, it is quite simple to develop and HMI for paramter downloading. Entivity and Iconics are two products that have fairly nice libraries for HMi development. Iconics Genesis is based on OPC so the intergration is completely seemless. I believe Entivity is also but, i have not had enough interaction with it to give it high mark.

If you have any questions, please feel free to give me a call 734-975-8108.

Thanks, I hope this helps

Sincerely,
Paul Horvath
Sr. Integration Engineer
Schnedier Automation
[email protected]
 
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Locus, Inc. will be releasing a 2.4 GHz license free wireless ethernet switch (802.11) soon. Please contact us at www.locusinc.com for more information. I believe this will solve all of your problems.

Mark Weiss
 
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