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Suggestions for a RS-485 repeater

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xxtigerxx

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I want to send a RS-485 more than 1200m so i what a RS-485 repeater.

Does anyone knows a circuit or a final product?

Thanks
:p
 

AdvaRes

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rs 485 repeater

Use max3192 IC.
 

xxtigerxx

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RS-485 repeater.

there is not max3192 in maxim!!
 

FvM

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Re: RS-485 repeater.

I see two points: MAX3291 isn't specified to extent RS485 at low baud rates above 1200m. It's specific preemphasis feature isn't effective for low baud rates respectively very long cables.

On the other hand, the specified RS485 1200 m limit is a convention without clear technical foundation. It's clear, that considerably higher distances are feasible at low baudrates.
 

AdvaRes

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Re: RS-485 repeater.

Hi all,
Hi FvM.
Actually the premphasis il always better in terms of distances and baudrate according to the figure below:
 

FvM

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RS-485 repeater.

Yes, I've seen the diagram. If you look at the preemphasis timing, it involves a 100 ns current raise. So the effect is reduced below 5 Mbps and neglectible below 1 Mpbs, I think. The diagram was made by connecting two point with a straight line or drawing a parallel line through one point.

But if the diagram is meaningful at all, you could extrapolate the conventional driver line to 100 kbps and below.
 

AdvaRes

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Re: RS-485 repeater.

FvM said:
So the effect is reduced below 5 Mbps and neglectible below 1 Mpbs, I think

Precisely, with a 1200 m you get a BW max of 3Mbps.
If this is not enough BW I'll use an ethernet connection if I was at your place xxtigerxx.
 

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RS-485 repeater.

The diagramm says 800 kbps for the MAX3291 and 400 kbps at 1200 m respectively 4000 ft. As I explained, the MAX3291 value is most likely an incorrect extrapolation.
 

AdvaRes

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Re: RS-485 repeater.

FvM said:
The diagramm says 800 kbps for the MAX3291 and 400 kbps at 1200 m respectively 4000 ft. As I explained, the MAX3291 value is most likely an incorrect extrapolation.

You're right FvM. I didn't pay attention for the feet unity in the diagram.
Thanks for correcting !
Cheers,
Advares.
 

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