Splitting RS422 Signals

[travasky]

Can RS422 encoder signals be sent to multiple receivers? I need to send the spindle encoder feedback to both the Oak as well as my spindle drive's secondary encoder input (for positioning the spindle during tool changes. Motor is not 1:1 with spindle). Alternatively, I could use an inductive switch to do the orientation sensing but like the idea of having one less component in the system and the accuracy of the encoder over an inductive prox switch. There are RS422 encoder splitters but they're in the range of 600-800 USD and may be more complex than is needed here. So, back to the original question, can the RS422 encoder signal be sent to both devices in a "dumb" way without added electronics?

[DannyB]

Assuming they are receiver-only, the RS422 standard allows for up to 10 receivers, wired exactly as one might think.
See figure 2 of this and other sources.

This definitely requires proper termination.

However, allowable current and other issues makes it somewhat impractical (they are limited to 20ma). See here and here for more than you ever probably wanted to know

This is one significant reason RS-485 exists even when you need just multi-receiver and not multi-sender/receiver.

Whether it works or not will depend on the drivers/receivers used, cable lengths, etc.

Otherwise, you have to play games with 422->485 and 485->422 converters or something similar. Note that 485 should be backwards compatible with 422 so you may be able to get away with one side of this.

Best answer you can get here is "try it". The standard at least allows for it

It definitely does not require hundreds of dollars worth of stuff to make this work even in the worst case (though it may require making some pcb's yourself)

[travasky]

I saw a recommendation on a similar topic on another forum to literally split them at a terminal block. The encoder runs about 12 feet to the control. I could terminate a foot or so away from the control and drive so the split cable lengths would be very short. Total cable run of approx 12-13 feet. As far as I know both the oak and the drive are simply receivers. Worth a shot?

[DannyB]

With these parameters, i'd say it's worth a shot.

You may have to terminate the cables with resistors at the oak/drive side.
(you are just about at the length it makes sense to do so).

Also, FWIW, here's an encoder splitter for 250 that should work http://encoder.com/blog/encoder-product ... er-signal/

(Again, you could build it yourself for less if you need to, but depends on time/effort/money)