dirty power - RFI Forum at eHam.net

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eHam.net Forum : RFI : dirty power

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dirty power	Reply
by KC6PGA on March 8, 2008	Mail this to a friend!
Ok, so it is not exactly directly ham radio related, but computer and electrical, so I am trying to communicate between CNC machine tools and PC computer using RS 232 with hardware handshake. Cable length is six feet. I have been having intermitant problems with buffer overrun on the CNC control side. I am thinking about pulling a new dedicated circuit with its own neutral and a isolated ground bonded to the main. I am in a total RFI pollution area with electric commuter trains running 60' from my place, three phase power switching large inductive loads, frequancy drives and plenty of other noise. I am considering an isolation transformer, but are there any reccomendations? Oh,BTW ham radio is difficult here and during commute times impossible with the broadband rfi from the bart trains hitting 30 over s9.

RE: dirty power	Reply
by KF7CG on March 9, 2008	Mail this to a friend!
By all means replace the RS232 cable as well. Though it is normally run in Unsheilded Twisted Pair type cable, run it in Sheilded Twisted Pair type cable. The sheild should only be connected at one end of the cable run. I would start with the shields conneted at the PC end, but it that doesn't work use the CNC side. In an environment that is that noisy ground loops in communications lines can be a problem. RS232 has two grounds a signal ground and an electrical (sheild) ground. Keep these separate and ensure that signal ground goes to signal ground and that the sheilds is not connected at one end. KF7CG

RE: dirty power	Reply
by KG4RUL on March 9, 2008	Mail this to a friend!
Have you considered a short haul fiber optic modem? From the catalog page: "In addition, it brings effective data communications to manufacturing environments. It can be installed in applications requiring very high data transmission rates, offers resistance to Electromagnetic Interference (EMI), and isolation from lightning-induced current surges and ground loops. " http://www.telebyteusa.com/catalog/products/9271.htm

RE: dirty power	Reply
by JOE_LEG on March 9, 2008	Mail this to a friend!
Hello Charles, You mentioned 'Machines' as more than one. If so are you conecting and disconecting the cable depending on which one you are D/Ling to or running the cables to a switch box and everything stays connected? Also are the baud rates matched? May even try lowering the rate a bit. Let me know the paticulars like controler types, comm program used, baud rate, error correction and I'll see if anything pops to mind. Being an intermitant problem, I'm betting cables, but need a bit more info. BTW, is the PC acting as the CNC controler itself for the machines? 73 Joe Leggett

RE: dirty power	Reply
by KC6PGA on March 10, 2008	Mail this to a friend!
I move the cable from machine to machine, but would love to have everything connected at some point. The problem is not so much with downloads as it is with drip feeding the programs in real time using the handshake to control data flow and prevent buffer overrun. The machine runs from it's own controller, but the program is fed in as needed from the PC. I know my settings are correct and the problem appears to be in the handshaking. I am going to try an optical isolator to positivly prevent ground loops. I think the best Idea I have had so far is to borrow a laptop and try that. It would pretty much eliminate the ac power as a factor and would appear to eliminate ground loops as well. Thanks for all the advice ADam

RE: dirty power	Reply
by KB9DT on March 10, 2008	Mail this to a friend!
Might be trying to go too fast with the RS232. By the time the source stops sending, the receive buffer may have already overflowed. Try a slower rate.

RE: dirty power	Reply
by JOE_LEG on March 10, 2008	Mail this to a friend!
Hi Adam, Sorry for calling you Charles:) You are shedding a bit more light now with your last post. You have NC machines fed line by line of code from your PC. As the last line is executed the PC sends the next line of code. Much like a tape reader (stop bits). Correct? If this is the case and you are using hardware 'hand shake', I'd suspect that. Like I said in a past post, need the particulars to truely help. Tell me what this 'Hardware' is. I do have a few years of NC/CNC machining behind me and another few years in IT.(though been awhile) 73 Joe Leggett feel free to EMail me if you prefer, it's in my profile.

RE: dirty power	Reply
by JOE_LEG on March 10, 2008	Mail this to a friend!
BTW check your pre posting file(S) to see if there is a needless call for an other line of instruction to be sent or appended to cause an over flow problem. Have seen that a few times. 73 Joe Leggett

RE: dirty power	Reply
by AA4PB on March 10, 2008	Mail this to a friend!
Check to see that your computer serial port is true RS-232 (i.e. puts out at least +/- 9 volts). There are some, especially laptops, that only do 5 volts and that doesn't leave much margin for noise. Make sure your machine and computer are powered from the same outlet so that you don't have a ground reference problem.

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