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Quadrature mode

quadrature frequency

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3 replies to this topic

#1 dam

dam
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Posted 21 September 2013 - 02:00 PM

Hi,

 

I have an incremental encoder (5000ppr) and it seems that the labjack miss some pulses when I use LJControlPanel. You say that the total number of edges should be less than 100,000 per seconds. So if I set A track to the timer0 and B track to timer1, can you confirm that the labjack will give correct result if the encoder does less than 100,000 / (4 x 5000) = 5 round per seconds?

 

Thanks.



#2 LabJack Support

LabJack Support
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Posted 23 September 2013 - 09:09 AM

Yes, I agree with your map.  If you are not streaming, and the only timers you are using is the 1 pair for this quadrature input, then it should be good up to 5 revolutions/second.

 

http://labjack.com/s...rs-guide/2.10.2

 

Can you cause the issue if you steadily move in one direction, or only with back-and-forth movement?

 

Does the issue go away if you go slower?

 

One thing to try is to enable Counter0 and connect one of the quadrature phases to that at the same time.  It will report the total number of edges it sees, and is handled purely in hardware so does not affect the quadrature timer input performance.



#3 dam

dam
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Posted 23 September 2013 - 11:05 AM

Can you cause the issue if you steadily move in one direction, or only with back-and-forth movement?

 
I can cause the issue if I move really fast in one direction (ie more than 5 revolutions per second)
 

Does the issue go away if you go slower?

 
Yes, I do not have the issue if I go slower.
 

One thing to try is to enable Counter0 and connect one of the quadrature phases to that at the same time.  It will report the total number of edges it sees, and is handled purely in hardware so does not affect the quadrature timer input performance.

 
I had done the following test:
- enable Counter0 and connect it to the A track
The counter does not lost edges and it seems normal as the Labjack support Counter at 3Mhz.
 

Yes, I agree with your map. If you are not streaming, and the only timers you are using is the 1 pair for this quadrature input, then it should be good up to 5 revolutions/second.

 
Ok thanks. Do you have any plan to create a Labjack which supports higher frequencies for quadrature mode?



#4 LabJack Support

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Posted 23 September 2013 - 01:30 PM

Not sure yet if the T7 faster, but if it is it will be something like 2x faster, not 10x.  To really go substantially faster requires hardware to track the quadrature, rather than doing it in firmware.  We have thought about some ideas for an accessory, but nothing in development at this time.

 

We have had customers use a Quadrature<=>SPI chip (LFLS7366R-S from usdigital.com) to do faster, as all our devices can speak SPI.

 

https://forums.labja...?showtopic=6065




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