NI Cables (10P to DE9)

[cbutcher]

I'm looking at the cable offerings in the NI shop and find the following options:

https://www.ni.com/en-gb/shop/category/cables.html?page=1&FrontendConnection=10-Pin,%20Male%20RJ50&f...

- 182845-0{1,2,3}

- 192190-01

What is the latter cable? It has no image available, it says "RJ50 10-pin Modular Plug to DB-9 (Male), 1m" in comparison to the others' "S8 Serial Cable, 10Pos Modular Plug to DB-9, {1,2,3} m (non isolated)"

Weirdly, on this page: https://www.ni.com/en/support/documentation/cable-accessory-guide/compactrio-system-accessory-compat...

it lists the 1m version of the first 3 cables as suitable for RS485 (for the cRIO I'm using), but not the 2 or 3m cables. Is there any reason for this?

Hoping someone with some experience using these cables for RS422/485 can enlighten me - reading the shop pages makes me feel like I'm peering around in a dark cave and hoping not to catch my hand on a sharp edge...

[JÞB]

The quick answer. RS-485 uses balanced pairs for TX and RX with a specific characteristic impedance that must be properly terminated. 1 meter is about as far away as you really want to be. You may have some luck using longer cables at lower baud rates but, the bit error rate will suffer. If the communication protocol has a rigorous CRC with error correction, (not just detection, actual error corection!) you can use the longer cables at higher speed depending on actual environment noise variables. NOTE: You will be opening the system to performing outside of engineering margins. Somewhere, down the line, some maintainence technician is going to get very angry at you when the communications fail intermittently.