Re: RS485 is bidirectional does it mean it is fullduplex?

Floyd L. Davidson wrote:

> And since we are *not* dealing with a power distribution system,
> your point seems to be less than appropriate.

It is more pertinent than you realise. The equipment I deal with
incorporates a range of measurement and control systems that includes
nano-volt signals, RS485 signals and 4-20mA current loop signals passed
over 150m of multi-core shielded twisted pair cable to the instrument
racks. The environment that this lives with is extremely noisy, features
high magnetic fields, extremes of temperature range and earth potentials
that can leap well off the normal reference level (and it is not the
noisiest environment I have worked with). Some of the communications
signals run in quieter areas and span about 50 different buildings on the
site. Each building has its own sub-station and the site has a SuperGrid
power feed (it uses short bursts of extremely high power at regular
intervals). So, as you can imagine, as a Systems Engineer with
responsibility for just some of the equipment on this site, I have to know
how the site earthing scheme works and what risks are involved. So in all
respects I am quite on topic for this thread and relevent with the advice I
have provided.

>>>>See my other post re isolated comms interfaces.
>>>
>>> Why not do some real research, and find out how it is actually
>>> done.
>>
>>Many of us have and employ this sort of consideration in our daily
>>practice.
>
> Reality check time: telephone cables all across the country and
> around the world are grounded every 3000 or 6000 feet.

Last time I checked around here the telephone company cables were
unshielded twisted pairs (but that was quite some while ago).

The other types of cable we use on site include unshielded and shielded
power cables, heliax coaxial cables and triaxial cables. I have to know how
to deal with each and every type.

--
********************************************************************
Paul E. Bennett ....................<email://peb@xxxxxxxxxxxxxxxxxx>
Forth based HIDECS Consultancy .....<http://www.amleth.demon.co.uk/>
Mob: +44 (0)7811-639972
Tel: +44 (0)1235-811095
Going Forth Safely ....EBA. http://www.electric-boat-association.org.uk/
********************************************************************
.

Relevant Pages

  • Re: Cutting Coaxial Cable
    ... Do I have to call my cable tv company to tell them to turn off power to ... NO, these cables carry RF, no dangerous voltages/currents. ... if you have to ask if you'll get electrocuted cutting a CATV ... regulations on signal leakage from CATV systems since the signals on the ...
    (alt.home.repair)
  • Re: Shielded mains cable
    ... would be needed to make the range of DSL on a given cable ... Trans-oceanic telephones cables used very high voltages. ... were powered in series like Christmas tree lights, ... range of DSL less than range of voice signals, ...
    (rec.audio.tubes)
  • Re: USB over Cat5 wiring
    ... "Active" cables have a chunk of electronics built into them that regenerates the signals and thus restores it to "as good as new". ... Only a limited amount of power is available from a USB connection. ... A powered hub doesn't draw power from its upstream connection, supplying both itself and any downstream demands from its power supply. ...
    (uk.comp.homebuilt)
  • Re: Bi-directional audio over power cable
    ... The main restrictions come from the cable, which is a big shielded cable with optical fiber inside, a pair of 37.5Ohm/km for power, and a pair of conductors for RS-485 control signals. ... the power cables are not individually shielded so I'll get noise from the RS-485 signals, I've no idea how bad that can be and if that can still be OK for voice; ... as I need bi-directional audio, I guess I have to shift the audio signals to higher frequencies to have both on the same line. ...
    (sci.electronics.design)
  • Re: Stop Sign and Traffic Light in same intersection?
    ... Two intersections in Long Beach in 1963 doesn't prove ... since I couldn't see the signals until ... arms or dangling assemblies at night, and especially if, in a power ... Drivers who continue to ...
    (misc.transport.road)