Dears , I have to exchange control from MM 440 to new inverter with positioning functions. Currently drive  stops according limit switches.  Now I want to go for encoder positiong. I would like to ask You for advice what options to choose. PLC on  the machine is CPU 315 PN/DP  and project is prepared in step7.   I thinking about usage of

6SL3210-1PE21-4AL0 Sinamics PM  5,5/4 kW (one step higher than motor -4kW)

6SL3246-0BA22-1PA0 CU250S-2 DP ( i have same in other place )

6SL3201-0BE21-8AA0 Braking resistor

6SL3255-0AA00-4JA2 AOP

6SL3054-4AG00-2AA0-ZE01   Card with Epos license

My questions are

1. I ve put CU to test in Hw config  and it seems to be possible to use it at step7.  Not sure if all firmware versions will be compatibile with step 7 .  I don't want to buy units which  I wan't be able to put in HW.  I didnt get from the seler firmware version . I ' ve wrote email to seler for further information.

2 . Because of cost limitation  I am planing to use old existing motor and  equip it with encoder. I think about absoulte  SSI encoder , or HTL    but  I would like to get Your advice . I checked that right now the drive is working  1305rpm what is divided by gearbox by 20.   Traversing speed is about 0,5m/s.  What resolution of encoder would You advice?  I thought about 1000 p/r   that gives  over 40k pulses per 1meter

3. I planed to use Epos function which I havent  used yet. Is it working ok for Step 7? I found document
https://support.industry.siemens.com/cs/ww/de/view/68109071

4. Should I consider any other solution form siemens  than mentioned above  on CU250 because of quite old equipment which  I am afraid may be shortly discontiued