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How to protect the ADM485 chip used in outdoor applications?

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Junior Member level 3
Jun 10, 2001
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Can anyone tell me how to protect the ADM485 chip when used in outdoor applications.
What sort of things to hang onto the data lines?
Any practical cct that you've used and robust enough for outdoor use that you can share is appreciated. Pls post cct if possible.

thanks. ..lak


This is what I use for my 485 apps.

Its an Isolated RS485 link

OOPS, guess the bmp never took.

check this:


blue snake

ESD protection

normally you protect the differentail levels on the two wries
with a bidirectional surppressor to GND on each line.
and you can take an current kompensation inductur.

rs485 cct

I've used a isolated link dc-dc converter for the +5v.
I've also used opto 6n137. protection using P6KE6.8 TVS diodes.

So the question is... for this isolated link, should I earth all terminals with a 3rd wire, or earth each with 100R resistor with a common 3rd wire or
should I join all terminals ground together with a 3rd wire.(no connection to earth) ? Its a mouthful ...I know.

Using only 2 wires, my 485 are damaged quite frequently esp. outdoor sites ,though there's no sign of lightning damage...system offline...sustained customer abuse... help..


rs 485

i think you are using step down transformer + linear regulator to get the 5 voltage supply

do the following
1- use bipolar supressior between the differintial terminal
2- use 3rd wire ( earth) and connect 2.2 nf/250 v between each erminal
of the transformer secondary and the earth.
3- connect 100 ohm between your circuit ground and the 3rd wire

plz email me if it gives good results

You can use datasheet RS485 isolated chips like ISO485 and check its protection circuitry ,ISO485 is from BURRBROWN (at now TI)

but do not use ISO485 at all because it has bug on receiving mode.

you can check isolated rs485 chips from maxim and others.

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