ACC-24E3 dual encoder feedback

Hello,

I'm requiring dual encoder feedback for each axis in our application. Currently we were using Acc-24e2 connected to the quadrature AB encoder, and a separate ACC-84 connected to an SSI encoder.

Electrically, it looks like I can connect both an ABQuad and an SSI encoder to the ACC24e3 at the same time - is this correct? Can the software read both simultaneously removing my need for the ACC-84 cards?

Thanks!

pnewhook,

Yes. If you use ACC-24E3 cards with Digital feedback option, you can bring in a quadrature encoder on A and B lines and a serial encoder on U,V,W and T lines as explained in the ACC-24E3 hardware reference manual.

Please note that enabling the serial encoder read will prevent the index (ChC) input from functioning since this pin is shared with Serial Encoder Enable signal. If you require to use the index mark on your quadrature input, for example during homing procedure as a position reference, then you can disabled the serial encoder read, finish the homing for quadrature and then enable the serial encoder.

It seems that in your application each axis has dual feedback. If the quadrature is being used for velocity/on-going phase position and SSI is being used for position/absolute phase position then there is no need for using index pulse out of the quadrature encoder.

Regards,

I have a follow-up question about dual feedback concerning the programming (after a correct hook-up has been made).

Clearly, in the PPMAC script language, motor[x].ActPos and .ActPos2 return the two encoder positions. However, at least for .ActPos, the actual value returned doesn't correspond directly to any motor structure value: experienced PPMAC C programmers have already found out the hard way that script language motor[x].ActPos corresponds to C language (M->ActPos - M->HomePos); that is, in the scripting language, the value relative to the captured home position encoder count is returned.

So here's the question: Where's .HomePos2 (or conceptual equivalent)? Should I calculate an interpolated value for it based on the ratio of the two encoder scales? If so, what should I do prior to the axis being homed?