Hello, I need to install an additional flex io rack, there is already on in the cabinet but the logical rack is full, it is the end of the line on the blue hose. Can I run my shielded cable from the RIO connector on the existing rack to the new one and assign the new one to any of the logical racks in logix 500 that have space available? I believe I need to be in program mode and just change the G file configuration to match what is installed. Also, what is the difference between the blue hose and any other shielded or unshielded cable? Could I run a comparably sized shielded cable from the top of the cabinet to the bottom where the new rack will be?

AB support told me that I can address it this way and that any two conductor cable may work but they will not debug or support it without the Belden 9463 or equivalent.

You need to move the terminator resistor. If you are not using them, then start doing so because eventually the noise generated by reflections on the signal cable is going to drive you nuts. You will need to change the "last rack" dip switch on the last rack and set it on the new one.

You can't just use ANY cable. You need to match the impedances fairly closely. As you increase the speed/distance, this will become a big problem, and you won't be able to predict what will happen because the resulting reflections and ringing that the incorrect impedance will cause can cause any node on the cable to stop communicating, not just the one you are adding. It is not just "twisted pair". It's actually equivalent to twinaxial cable which is an old IBM mainframe cable design.

It has to be shielded because unfortunately AB chose to use a signal format which is susceptible to interference as well. If you can get the impedance right (78 ohms), twisted pair cabling however should do pretty close to the same shielding. Remember this important detail though. Arcnet (aka Controlnet) and Ethernet both have nulls in their signalling around DC. The protocol is designed such that the NIC cards filter out everything under about 100 Hz including any 60 Hz induced signals in their magnetic interfaces (the NIC card has an isolation transformer and a couple other inductors) which makes it pretty much immune to almost any interference.

Since the DH+/RIO protocol was not designed with a similar null, you are playing with fire if you try to skimp on the shielding because twisted pair is meant to handle relatively high frequency interfering signals, not low frequency ones. Each half-twist induces an opposite polarity signal from any nearby stray EMI fields and the two cancel each other out. However, the half twists have a relatively small aperature. With the relatively low frequency interference that DH+/RIO is susceptible to, twisted pair probably won't give you any effective protection.

It works fine for current loops partly because they usually filter off all kinds of noise in the input cards (DC filtering) and because it's a current-based signal instead of voltage based so the coupling to free space in the circuit is relatively weak relative to DH+/RIO line receivers which are voltage-based.

Thanks for the reply, that sounds like enough evidence to convince my boss that he just needs to buck up and get me some blue hose. There is a resistor on the last one so I will move that and adjust the switch when I have the opportunity to do the changeover. Thanks again.

The manual tells me that the last rack switch is only used for PLC-2. I am going to leave it in the position that the current last rack is in except for the addressing switches. FYI I guess.