Remote site communications options


Thread Starter


We are working on a Control system for the local municipality. They want to control their well houses based on the level in the standpipe. We have the control system worked out. (AB Micrologix PLC's in all locations) What I want to know, is what everyones opinion on how to do the remote communications is. We are looking at three options.

1. Leased line (least favorable) - Its reliable and easy, however it is very expensive over the long term.

2. Wireless Ethernet (Most Favorable) - We have been working with Wireless ethenet links for PC networks for a few months now, and the links seem easy and reliable, however I don't know how well they would work in a control situation. We would install the New AB ethernet modules at each site and it would also give the ability to have a PC port available at each site and to easily do remote programming.

3. Wireless Data - (ie Datalinc, or Esteem)I guess this is the tried and true way of wireless - unlicenced, however its no less expensive then our ethernet solution, and we loose some options. (but maybe with reliability as the bonus)

Please, I am very new to remote data, and would appreciate any help.

We are successfully using unlicensed Spread Spectrum RF for water/wastewater
monitoring and control at distances up to 20 miles. However, we have learned
that the larger the packet you transmit, the lower the chances of successful
transmission during inclement weather. TCP/IP wrappers adds an additional
overhead to each message of around 32 bytes.
For comparison a Modbus message to get/set all the DI/O at a remote site is 8
bytes total. Quite a difference.

Relatively large messages consistantly failed while small messages almost never failed during bad weather.

Just something to consider....


Alan Brause
I found it a bit odd how you mention Data-Linc with wireless serial, but not
wireless ethernet. We've used their SRM6200 Wireless Ethernet devices in
the past. In fact, we're going to be quoting 13 wireless modems from
Datalinc today. Their ethernet product is very robust, and it works well in
very noisy environments. We set one up for a customer (in his office inside
building, with only the 6" whip antenna), got in the car, went to the remote
reaches of his facility, and plugged in the modem and were able to
communicate with the master. Really powerful technology!

My experience on these three options is:

Leased Line: Not always reliable, it depends on the personnel at
the phone company. At some locations I have receive excellent support,
other places it will take a week for them to fix a problem ( it
always my problem, even if its theirs ).

Ethernet Radio: Is the best, but it is about $500 - $1000 more
expensive per unit than serial. This also provides the
ability to for peer-to-peer comms.

Wireless Data: I have used MDS for this, they have better diags
than the DataLincs and are less expensive, don't know about the
other brand.

My number 1 requirment for telemetry apps is remote programming.
I do not drive around programming PLCs unless I absolutely have
to. I like to see the HMI and the PLC program at the same time
from the central computer system. I can have the technician that's
doing the installion work perform the checkout with me. This is
easy to set up with ethernet. You have to do some planning to
make this work with serial.

Jay Kirsch
[email protected] <mailto:[email protected]>
The reason I don't see Datalinc as a good solution for ethernet is strictly based on price and experience. Datalinc is consistantly twice as expensive as the competition. We have been installing Wi-LAN wireless ethernet bridges with great success. One of our sites we had to actually install an attenuator to keep the signal strength below saturation. I don't know all the details of Datalinc, but Wi-LAN modems are SNMP manageable which makes things a lot easier.

Maybe Datalinc is twice as good, I don't know, but it seems as though Wi-LAN works just fine, and at half the price....hmm, not a hard choice.

Thanks for everyones help. I think we will stick with wireless Ethernet, unless someone has a good reason why not.

Locus Inc. ( will release it's OS2400-Ethernet radio at the ISA Houston show. It will list for $1495 and is an Ethernet switch. You can locate information on it and other Locus serial radios at their web site. Locus also has a number of Applications Engineers on staff who can answer all of your questions regarding industrial wireless ethernet.

Mark Weiss

Aslam Sherule

I accidently came across your question. We are exactly in this business. We have deployed many telemetry and telecontrol solutions. Visit our website

Please feel free to contact me if you need further information.

Aslam Sherule
Director of Technology
Telemetry Technologies
Suite 2250
3340 Peachtree Road NE
Atlanta, Georgia 30326

404-231-0021 Office
404-261-3669 Fax
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