[daedalus]

Hi,

Im currently in the middle of a rewire at the moment, and would like to add support for using a mesa anythingio card as well as the parallel breakouts i have at the moment.

Im doing this so i can run the drives as pwm-mode torque controllers, and close the control loop in EMC. The problem is i need to connect the encoders both to the drives and the mesa card.

The mesa card has single ended encoder input. Is it ok to just wire gnd, and +A,+B,+C to the mesa card and the VSD-A in parallel? Are there grounding issues i need to worry about with doing this?

Tom

[Xerxes]

Hi Tom,

It should work especially for small power motors where currents are low but you definitely need to pay attention to grounding. For large motors and/or safe (smoke free) operation I would build an optoisolator circuit between the encoders and Mesa card.

Please see my attached schematics that was designed for USC board for similar purposes. You may add second optoisolator if you need also index channel. I guess this would work also with Mesa.

[epineh]

Hi Xerxes, with this type of application should the grounds be kept completely isolated as you have drawn and not tied together ? That would make sense to me as far as isolation goes but the electrician in me wants to tie all grounds together.

It is something I have wondered about.

Cheers.

Russell.

[Xerxes]

You could be creating a ground loop that may cause malfunction or even destroyed components. When drive starts drawing many amps of current, it makes notable voltage drop in ground cables that may cause problems to Mesa card. It could also pull amps of ground current from Mesa card which may not like it.

I think it would be possible to avoid such problems without isolation too, but in that case you need to know exactly what you're doing. Isolated grounds not only eliminate the problem but are also safer choice when something goes wrong, that's why I suggest it.

You definitely can still ground drives when using optoisolator. Purpose of isolator is just to eliminate ground current from flowing via Mesa card.

[epineh]

Cool that is wanted to hear, thanks for the advice, I am trying not to destroy any more components, isolated ground it is.

Russell.

[daedalus]

Thanks for the advice, and for the schematic.