Author Topic: fseq and fpp and 25ms  (Read 1187 times)

Offline charleskerr

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Re: fseq and fpp and 25ms
« Reply #15 on: March 09, 2014, 03:20:52 PM »
There is also the issue of data run lengths.  If one goes to 2MBaud, one has to start considering the degradation of the signal.  It also starts to become import to run the ground line (Contrary to popular belief, RS-485 is not a 2 wire electrical specification, it does have a ground line).  I ran a show with my SSD protocol (A 2MBaud+ data rate), and noticed it was very particular about having a good ground and I had to start being aware of the data line lengths.  Not saying one will experience an issue, just stating we started to experience a few items (and for every factory that we have wired, it is also imperative that we follow the electrical specification).
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Offline Timon

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Re: fseq and fpp and 25ms
« Reply #16 on: March 14, 2014, 11:12:12 PM »
I suspect you were having some common mode issues. RS485 does not use the ground to get the data through but to reduce the common mode which can disrupt the signal. If you run isolated RS485 then you don't have any possibility for common mode issues.

The place you need isolation is any spot in the chain where the device gets power from the AC line. That's where common mode issues can crop in. At higher data rates common mode can effect the data more easily. The SSC's don't need any isolation since they get their power over the cable. So if you isolate all line powered devices and then your not likely to have any data problem.

 

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