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Frequency output: phase and relation to streaming input

timers streaming

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5 replies to this topic

#1 mikelwrnc

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Posted 28 October 2014 - 12:40 PM

Is it possible to use two timers to send frequency output at the same frequency but different phases? (i.e. 90 degrees from one another, so the pulses alternate). I believe that this is possible with the T7, but wanted to check if it might also be possible with the u3 that I already own.

 

Also, if I have analog inputs in streaming mode simultaneous with timers doing frequency output, should I expect any consistent relation between these? Are they driven by the same clock, and should I expect any phase difference between the two if running at the same frequency? Presumably the sample acquisition takes some amount of time that depends on the number of channels being sampled, but could I expect the sample acquisition start time to occur simultaneous with the timer pulse onset? (I'm using the input to monitor the output of the device that is receiving the frequency output, so if the send and sample events are simultaneous while the communication to and update on the device takes time, I might need to add a phase delay to the sampling [possibly by adding other dummy channels before the one I want?] to be able to measure the device once its updated)



#2 LabJack Support

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Posted 29 October 2014 - 04:46 AM

No. The timers on the U3 lack the ability to vary their relative phases.

 

 

The output timers are all run from a single internal hardware counter. Stream is run from a separate counter. Both of the counters are clocked from the same crystal. Depending on the settings used, the frequency outputs can phase locked to the stream scans. The bottom line, the two systems (timers and stream) run independently from the same clock source. So, it is possible for the "sample acquisition start time to occur simultaneous with the timer pulse onset" but there is nothing guaranteeing that it will.

 

 

This is getting into small details of the device. It may make more sense to use low level functions where you specify the clock divisors and counts.



#3 mikelwrnc

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Posted 29 October 2014 - 06:55 AM

The output timers are all run from a single internal hardware counter. Stream is run from a separate counter. Both of the counters are clocked from the same crystal. Depending on the settings used, the frequency outputs can phase locked to the stream scans. The bottom line, the two systems (timers and stream) run independently from the same clock source. So, it is possible for the "sample acquisition start time to occur simultaneous with the timer pulse onset" but there is nothing guaranteeing that it will.

 

Is this the case with the T7 as well? 



#4 LabJack Support

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Posted 29 October 2014 - 08:39 AM

The T7 is similar. There are two different hardware counters that can be used to drive the DIO_EF (new name: "extended feature" instead of "timer") outputs. However, the T7's DIO_EF outputs have a new PWM mode with full phase control. The relationship to stream is the same as with the U3; the outputs and stream are all driven by the same clock, but are in no way synchronized.

 

If you need to synchronize something with stream then stream_out is the way to go. With stream_out you can specify exactly where in your scan an output will be updated.

 

http://labjack.com/s...form-generation

 

http://labjack.com/s...mode/stream-out



#5 mikelwrnc

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Posted 29 October 2014 - 09:48 AM

If you need to synchronize something with stream then stream_out is the way to go. With stream_out you can specify exactly where in your scan an output will be updated.

 

And "stream_out" is only a T7 feature, right?



#6 LabJack Support

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Posted 29 October 2014 - 01:21 PM

Yes, Stream-Out is a T7 feature.  The UE9 has a limited version called Stream-DAC.  The U3 (and U6 and U12) does not support any type of stream output.




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