Jump to content
OMRON Forums

Maximum encoder signal frequency


bmartins
 Share

Recommended Posts

Hi,

 

I have a PowerBrick LV crate and I want to read a 20MHz quadrature encoder with it. The manual states that "the absolute maximum signal frequency is one fourth of this clock frequency. It is generally recommended that a 20% safety margin for signal imperfections be provided". So, if I set Gate3.EncClockDiv=0, I would have 100MHz of sampling frequency and 25MHz of maximum signal frequency, 20 MHz with the 20% safety margin being considered, which would work great for my purpose.

 

However, the same section of the manual states that "Presently, the ASIC itself can accept higher signal frequencies than the encoder receiver circuits on Power PMAC hardware. These receivers are limited to an absolute maximum 10 MHz signal frequency (40 MHz count frequency). With safety margin, no signal frequency greater than 8MHz should be provided."

 

So, am I really limited by 8MHz? Or is this restriction gone? How could I check my hardware capability?

 

Thanks!

 

Bruno

Link to comment
Share on other sites

  • Replies 4
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

The 20% safety margin really is to account for the quality of the encoder duty cycle and phase offset (signal imperfections), not the actual circuits used. Although we specify in print the line rate is limited to 10 MHz by virtue of the input buffers there is headroom so you should be able to achieve the 10 MHz with quality encoders.
Link to comment
Share on other sites

The 20% safety margin really is to account for the quality of the encoder duty cycle and phase offset (signal imperfections), not the actual circuits used. Although we specify in print the line rate is limited to 10 MHz by virtue of the input buffers there is headroom so you should be able to achieve the 10 MHz with quality encoders.

 

I see. So the maximum achievable is 10MHz right? No way to go up to 20MHz? It is a PowerBrick IMS LV

Link to comment
Share on other sites

The line receivers are rated only to 10 MHz signal frequency. At 10 MHz and above, if you were to look at the output signals from the receivers into the ASIC, you would consider them "analog" signals, looking like they had an RC time constant. Most parts would operate successfully at quite a bit above 10 MHz -- I have run successfully several times at 12.5 MHz, but then you have to worry about part-to-part variation and possibly temperature variation.

 

That said, you can try higher frequencies without worrying about damaging things -- it would just lose counts if you go past its real capabilities. Look for the ASIC's "count error" status flag.

Link to comment
Share on other sites

Guest
This topic is now closed to further replies.
 Share


×
×
  • Create New...