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RS485 signal switching

> Mike Harris>>>

>>> HV reed relays may be worth a serious look. >>> Will be a whole lot easier than a semiconductor solution. >> >> I have lots of experience with various 10kV-rated relays, >> reed-type and otherwise. They're not quite fast enough. > > How about a number of lower-rated reed switches in series, > in the same coil..?

Would that be fast enough for the OP's 500Hz requirement?

Anyway, the problem with reed switches isn't the switch gap, which is in vacuum and typically can handle very high voltages, but with the insulation between the reed's leads and the low-voltage magnetic coil. I've used may HV reed switches made with special potting compounds, only to have them eventually fail with a carbon breakdown path forming inside the potting material between one lead and the coil.

10kV insulation is a considerable challenge over say 5kV. 
--
 Thanks,
    - Win
Reply to
edoreshef
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use a thansistor to realize a compartor is OK.

Reply to
slebetman

I would assume that switching loads in and out in this manner would introduce glitches into the line. If you're using RS-485 like most people and putting half-duplex asynchronous serial onto it then it should be pretty robust to glitches.

"Pretty robust" doesn't mean "immune", however. If I were designing a system with this sort of thing in it I would pay close attention to the communications protocol built on top of my RS-485 bus and asynchronous serial transceiver. I would make sure that it has a means of error detection and correction, probably backward error correction with a checksum, acknowledge and repeat structure.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply to
Tim Wescott

Most people use RS485 with such protocols anyway since a bus with more than 2 nodes on it would at the very least need some sort of arbitration. So I assumed that's the scenario described by the OP. But yes, make sure you use the appropriate protocol for the job.

Reply to
slebetman

If you use a relay have passive pull up/down resistors on the line to put it into a known state whilst the wipers are flying. AFAIR the pulls are A to -ve and B to +ve.

The simplest wire is multiple RS485 line drivers and Enable/Disable each as required.

--
Tony Williams.
Reply to
Tony Williams

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