Encoder connection to multiple PLC's

[mjrx]

I have a motor feedback encoder going to back a servo drive. I need to also wire that same encoder to a PLC counter card to monitor position. There is not an encoder out on the servo to use for this, as some servos have. To complicate matters, I need this encoder to also go to a second redundant PLC. It cannot be switched between the PLC's as it needs to be live to both PLC's so the redundant PLC can keep track of position - in the case the redundant PLC gets called to action, it needs to know where (position) the other PLC left the machine. So in a nutshell I need one encoder to be paralleled across three devices. I know I just can't parallel them because of possible voltage level differences, loading issues, feedback problems, etc. Is there some COTS isolation device I can use for this, do I have to get creative with diodes, or other iso method I could try? Thanks in advance.

[RussB]

If you actually have a system that is so important to need redundant controllers, you need to add another encoder to the system to get a 100% reliable redundant position. Also I would never use a servo motor that did not have its own encoder or is this only needed for speed control?

[Crossbow]

Be careful wiring an encoder to so many things. It's going to degrade the signal, and it's very low voltage and prone to noise to begin with. Why not just have more than one encoder, or have one PLC read the encoder and repeat it out a high speed pulse output?

[panic mode]

what type of encoder we are talking about? what is the nature of the interface?

[mjrx]

Its just an incremental quadrature 1024 ppr encoder, used for feedback between motor and drive. I found an encoder signal broadcaster that takes one encoder input and rebroadcasts it, optically isolated to up to four different devices. It is made by BEI. Thanks for the answers, I am now leaning more to a seperate encoder, and it will probably be a 16 bit absolute type.