how to choose incremental encoder?

[seyyah]

I want to design a closed loop speed controller for an induction machine. I plan to use an incremental encoder for speed feedback. Motor speed will be between 0-5000rpm. For this purpose how must i choose the encoder? How much pulses must it be or what to care?

 

[shangwa]

Hi,
Why don't you use a tachmeter for speed feedback
instead of encoder for poistion feedback???

Regards,

 

[IanP]

Majority of shaft encoders (within reasonable price range) are rated for output frequency below 100kHz (although they may be rated for 10 000 rpm or more).

I don't think that for speed control you need more than 100 ppr.

So the selection criteria should be based on mechanical properties (max rpm) of the encoder and electrical properties of the reading circuit ( (max input frequency; high speed digital I/O cards for PLC or PC are not rated for square waves above 20kHz)..

Example:
RPM = 5000
Encoder's PPR = 100
Output Frequency at Max RPM = 500khz .... well above max frequency response.

Solution: 10:1 speed reduction (by small belt or gears)..

 

[aym_qunibi]

i recommend you to use tacho generator thus you do not need position control, and if you will use an encoder pay attention to the reading device if it is in the frequency range of input pulses, and pay more attention if you use a PLC to read the pulses,so you check if a high speed counter available.. :wink:

 

[lcg22]

how about using a counter to measure the encoder output? then the high output freq is not a problem. most counter has a 20MHz+ time base. take an example NI 6602.