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Using the U3 to determine angle of rotation


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#1 drail24

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Posted 25 June 2013 - 02:09 PM

Would it be possible to use the U3 and a hall effect sensor with a toothed wheel to determine the instantaneous degree of rotation of a running engine? I understand the U3 has a quadrature mode that can be used for similar type functions and that you can fairly easily determine RPM and direction using a hall sensor and trigger wheel, but does anyone have any ideas how to read incremental degrees of rotation. I am trying to record other sensor data that should be occurring during a particular degree of rotation (say 30 degrees). I would like to constantly monitor the degree of rotation (from 0 to 360) and then overlay that information with the other sensor data to determine what readings I am getting at various degree angles. The rpm range would vary between 0 and approximately 5000rpm's. I'm thinking the easiest thing may be to buy and off-the-shelf incremental rotary encoder, affix it to the engine, and then read the output signal from it using the U3. However, I have hall effect sensors and trigger wheels already available and thought it might be possible to use those instead.

#2 LabJack Support

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Posted 25 June 2013 - 02:14 PM

The reason to use quadrature is when you need to track forward and reverse motion. If your engine is always moving the same direction, you can just a basic counter to count the pulses from your 1 sensor. You might want some other sensor that gives you some sort of signal once per rotation, so you can have a known location to count from.

#3 drail24

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Posted 25 June 2013 - 05:09 PM

Ok, I see. So it is more a matter of getting a trigger wheel with enough teeth and enough separation between teeth to accurately read each one. The number of teeth will determine how fine a resolution can be achieved (each tooth represents some amount of degrees). Would it be feasible to still use a single sensor but have a missing tooth or a particular tooth with a different signature that would represent the starting count or reset point. Thank you.

#4 LabJack Support

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Posted 26 June 2013 - 08:46 AM

Nothing real obvious occurs to me, but depending on the exact nature of the sensor and your setup perhaps you could have it where most of the teeth give you a high voltage of 2.5V but one tooth is closer and gives you a signal of 12V. You feed the signal to directly to 1 counter with just a series resistor to limit current from the 12V pulse, and this counter counts every tooth. You also feed the signal to another counter, but with a /3 voltage divider so only the 12V pulse results in a signal big enough to cause a pulse.

#5 TonyF

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Posted 27 June 2013 - 03:32 AM

Would it be feasible to still use a single sensor but have a missing tooth or a particular tooth with a different signature that would represent the starting count or reset point.


I have had to do similar things and I have found that sometimes the simplest way is to use a second sensor, which just gets a single pulse per rev. (or two if you mount in on the cam). Then use the signal from this sensor to start the counting on the main sensor.
You may be interested in the topic that I started a month ago on quadrature/timing and counting coding.


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