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quadrature encoder


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6 replies to this topic

#1 Jason S

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Posted 20 February 2013 - 09:05 AM

I have used LabJack U12 and UE9 before but it's been a while. Which of the LabJack models have good support for quadrature encoder inputs? By "good" I mean that they capture all 4 state changes per cycle and can handle reversal of direction / jitter correctly. I have a 1024 counts/revolution encoder I plan to use on a motor going up to 6000RPM --> up to 102,400 counts per second. I would like to take regular samples of some analog input voltages and at those same sampling instants, capture the encoder count. Which models is this possible with? We have a limited budget so I would like to find the most economic solution that meets our needs, and the LabJack models are good candidates if I can confirm they will support this use.

#2 LabJack Support

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Posted 20 February 2013 - 02:43 PM

All the newer devices (everything except the U12) have timers that can be configured as quadrature inputs:

http://labjack.com/s...s-guide/2.9.1.8

The problem is that your quadrature is too fast. You are expecting up to 100k counts/second, which means 400k edges/second. The limit for the U3 is 30k edges/second (if not streaming), and

http://labjack.com/s...ers-guide/2.9.2

The U6 is the same. The UE9 is rated for 100k edges/second.


Perhaps you could use a chip to track the quadrature and have the
LabJack periodically get readings from the chip over SPI. Such as the
LFLS7366R-S:

http://www.usdigital.../interfaces/ics

#3 Jason S

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Posted 22 February 2013 - 08:02 AM

The problem is that your quadrature is too fast. You are expecting up to 100k counts/second, which means 400k edges/second.

No, I expect up to 100k edges per second. 1 count per edge. (only 25k pulses per second)

Thank you for the numerical data, it sounds like the UE9 is the right choice. (What about the T7?)

Perhaps you could use a chip to track the quadrature and have the
LabJack periodically get readings from the chip over SPI. Such as the
LFLS7366R-S:

http://www.usdigital.../interfaces/ics

ok, thanks for the pointer.

#4 Jason S

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Posted 22 February 2013 - 08:05 AM

p.s. has there been any thought to adding another forum area for "Selecting the right model"?

#5 LabJack Support

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Posted 22 February 2013 - 10:06 AM

Good idea on having a forum board for product selection. We are working on new web site stuff to help compare devices, and will see what that leads to. Is your encoder 1024 pulses/rev? Or is it 256 pulses/rev and thus with 4x counting you will get 1024 counts/rev? We have not looked at the quadrature edge rate limit on the T7 yet, but I will see if someone can do that.

#6 Jason S

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Posted 25 February 2013 - 08:08 AM

We have not looked at the quadrature edge rate limit on the T7 yet, but I will see if someone can do that.


How difficult is it to give this information? I need to decide which to buy, T7 sounds more attractive for other reasons.

#7 LabJack Support

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Posted 25 February 2013 - 03:34 PM

Did some quick testing and 240kE/s is the error free max. That is a real number. The edge-rate specs in the user's guide are usually halved to be more conservative and account for variability.


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