Real-Time Measurement and Control

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Problem synchronizing position encoders measurements using cDAQ 9174

Hi,

The main purpose of my work is to read simultaniously and compare signals of two diffrent encoders.

I am using cDAQ-9174 on which is mounted an NI9401 DIO Module.

To make sure of the sychronisation of my position encoders (ctr1 and ctr2) measurements. We duplicated a signal so that both encoders would have the exact same input in order to see if they are measuring the same. the set up is described in the ''Setup'' image.

The VI I am using is ''Synch.vi'' joined to this post. I created the VI based on two examples :

https://forums.ni.com/t5/Example-Program-Drafts/Synchronizing-Two-Counter-Tasks-in-NI-DAQmx/ta-p/349...

and

 http://www.ni.com/example/31081/en/

I am using an arm start trigger to ensure that both encoders begin measuring at the exact same moment and i use a third counter (ctr0) to generate a pulse train that i use as a clock signal for both encoders to ensure their synchronization.

According to NI engineers with whom i had an e-mail exchange, This VI should work perfectly and there should be no problem.

The configuration we used is also correct according to them.

The signal I am using as an input could reach a frequency of 3MHz.

The resluts are joined to the post.

i visualised those results I got as described in the ''visualised results''. a zoomed area of those results is in ''zoomed area of results'' to describe better the results.  

 

It seems that there is a delay of the reading between the encoders. the same signal is read by both of them but with a delay.

What could be the origin of this problem ?

 

Hassen.

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Hassen13,

 

This forum is for Real Time Measurement and Control, that's probably why you haven't got any replies. Try posting it on the LabVIEW forum first.

 

In the mean time, have a look at this whitepaper to see if it gives you any help

 

http://www.ni.com/white-paper/4105/en/

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Hi

I will try that.

Thaks a lot.

 

Hassen.

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