Lightning vs Spread Spectrum 1

[ICman]

I was considering the use of Spread Spectrum technology to transmit control signals (analog/discrete inputs and outputs) from one building to another. These buildings range from 100 ft to 1 mile apart.

I was told that it would never work, due to the numerous, strong thunderstorms that roll across north Texas. They told me it would knock out the signal and cause a loss of control (if the signal is "out" for a few seconds).

Has anybody had similar experiences?

I'm trying to save the cost of running conduit/cable just for a few signals. Any suggestions?

 

[melone]

Does it have to be sent via cable that you run?

 

[Lewish]

It depends on the type of Spread Spectrum implemented, whether it is a frequency hopper or a PRN. PRN is more succeptible to ramdon noise.
Get the jamming ratio specification for the equipment under consideration to determine if it is acceptable for the job.

 

[ICman]

Thanks for the replies. Additional info:

In one particular case, I'm trying to get two 4-20 mADC signals from transmitters located on compressors to a control building, housing a PLC. I estimate the cost to run a conduit at about $10K, whereas a wireless system would be about half of that.

A couple of the radio systems I found use "hopping" technology. The systems convert the 4-20 signal to a digital stream, transmit it via radio, then convert it back.

The systems I've researched include those from Omnex, SCADALink, and WISE. They mostly use 900 MHz frequencies, but others are available (2.4 GHz, 50 MHz). All are license-free.

... Steve L.

 

[nbucska]

What is the bandwidth and the max. delay you can tolerate?
It is possible to add ECC and repeat if corrupted. <nbucska@pcperipherals.com>

 

[robertjo24]

I have used 900Mhz spread spectrum for years in the automation and control industry, and I must say that the only time I have ever had a problem with lightning was when it knocked out the power,(or struck the antenna.
The 900Mhz spread spectrum technology is well proven in the industrial setting. I would not hesitate to install a system for this application. I would be very interested to converse with those who would dissuade the use of this system for this application. They wouldn’t be from an electrical contractor would they (to run the conduit)?
If you have specific questions regarding the application of spread spectrum for automation and control (900Mhz, 2.4Ghz, 5.2/5.7Ghz), please feel free to contact me for more info at joroberts24@earthlink.com.
A properly engineered control system will not allow a brief communications outage to cause a loss of control. The systen should run as is until signal is restored.

 

[robertjo24]

One additional thought:
Do you have an additional comm. port on the PLC at the control point? If so, you can place a small PLC ($250.00, DL-05 @ automationdirect.com) at the compressor (capable of four AI and several DI &DO), and have the control point PLC poll the PLC at the compressor. The devices could be linked via external RS-232/422 data radios. I recently engineered the same scenario for one of our stations. This is very cost effective and simple to implement. The integrated RTU/data radio devices I have seen have less TX power that the dedicated data radios, reducing overall range.
If you have further questions, please do not hesitate to contact via email. I would also suggest a posting in the “Programmable Logic Controller (PLC)” forum on this website.
There are many respondents there smarter than me on automation and control issues.

 

[ICman]

Thanks Robertjo24 for the insight. The person that thought lightning would have a detrimental effect is an instrument/control specialist (35 years) who seems to know his stuff. Several sites are located in north and east Texas, an area that is known for some powerful thunderstorms. We have a UPS with batteries for backup power.

I don't know if I would trust control functions to wireless, but certainly data gathering should be okay. Some sites have extra comm ports, some don't. I have looked at the option you described - passing serial data - but it really isn't viable in most of these applications.

Yes, perhaps this post should be in the PLC forum, but I thought this forum could perhaps better address the specific question.

Feel free ask if you have questions.

. . . Steve

 

[djs]

Hello;
We use spread sprectrum radios to transmit telemetry all of the time. However like robertjo24 we use PLC's at each end. An example is to use A-B micrologix PLC's and MDS 9810 radios. total cost of around $4K.