Rotary encoder best option here?

[JZerb]

A typical encoder and a very economic one (I often buy Sick optical encoders)with 2048 PPR connected for four fold counting will still be under the 100Khz limit of the micrologix 1400 and will give you high resolution. Combined with the gear ratio you mentioned you will achieve excellent positioning precision.

1750RPM / 60 = 29.167 RPS
2048PPR x 29.167 = 59734.016 PPS or about 60Khz
2048PPR x 4 (Four fold) = 8192
8192 x 350 (Gear ratio) = 2867200
You can see where this is going,after you've figured out how many motor revolutions per one table revolution you will have very high count to divide over your 360 degrees.

thank you for this. im still reading and re reading this to digest the math but i think im understanding it. the only part youve got me lost is the (Four Fold) spot. and also the motor will more then likely not run at 1750 RPM, thats just what it would run at if i were to put 60hz to it from the VFD. Typically i run about 30-40hz to get the desired results. would you then downsize the PPR on the encoder to match? or as a general rule should i always size an encoder based on the motor name plate RPM and Hz?

 

[kalabdel]

thank you for this. im still reading and re reading this to digest the math but i think im understanding it. the only part youve got me lost is the (Four Fold) spot. and also the motor will more then likely not run at 1750 RPM, thats just what it would run at if i were to put 60hz to it from the VFD. Typically i run about 30-40hz to get the desired results. would you then downsize the PPR on the encoder to match? or as a general rule should i always size an encoder based on the motor name plate RPM and Hz?

The four fold is me not knowing much about RSlogix and talking Siemens instead. I assume RSLOGIX will have something like that but I won't have time to look at the software till the end of the day. It's basically counting the rising edge and falling edge of the two optical sensors in the encoder. It increases resolution and enable detection of direction of rotation.
You can loosely calculate motor RPM at the frequency of your choice by scaling RPM to Hz 1750/60 and then multiply the product by the expected frequency (30-40) and in this case you will get lower resolution which means you can up the PPR of the encoder you buy but you have to be careful not to exceed the PLC's max frequency of 100Khz when the motor runs at 1750 RPM. I would suggest figuring out first the motor revolution to table lrevolution rate before specifying the encoder.