Angular velocity measurement in continuous mode with NI-9401 card

[Skirpt]

Hamed,

It looks like you have fixed the error that you were having before. Unfortunately I am unable to test this. Have you tried running it to see what results you get? I am not sure what you will need to put in the offset and phase. That more depends on how your subVI interacts with your VI. I think the best way to find the correct values would be to try it out. 

Sorry that wasn't too much help. Let me know how this goes.

[Hamed26]

Thanks.

Unfortunately this deterministic approach with buffered counter is working very bad, with very inaccurate results. While my angular velocity should be around 1500 rpm it is showing me - 0.07 RPM !!! and the other point when I export the Angular velocity data from the graph to a excel file, it has only a few number of datapoints. Unlike what I was expecting that we define a sampling rate and samples to read for this, but unfortunately it only shows a few number of data points. I added a collector block becasue first I could not see any data on my graph and since I wanted to collect the maximum samples, I defined the number of data points to be collected to 100,000,000 data points. So, In conclusion:

1) Very inaccurate or in other words false results (0.07 RPM instead of 1500 RPM)

2) Very low number of data points (about 10 samples when I was running my machine for about 10 seconds and it should have shown 20,000 samples due to the samples to read that I defined )   

Please have a look at my attachment file.

Thanks

[Cavarval]

Hello Hamed,

There are several factors here.

About the inaccurate readings, verify you are using an appropriate decoding type. X4 is more sensitive but it is prone to errors in environments with vibration. Also it is only valid for quadrature encoders, so please verify that as well.

What about the raw data? Is it possible that the data processing is leading to wrong velocity values?

About the low number of points, note that you are using a Waveform Graph. This type of indicator does not save any type of historical data, so if you export it, you will only get the latest data set. You have two alternatives:

1. You can use a Waveform Chart instead. Waveform Charts save historical data and you can actually specify the number of data points the chart will store increasing the Chart History Length by right-clicking the chart.

2. You can configure the tasks to perform TDMS data logging instead of simply exporting the chart to excel. Se this article for an example. The TDMS can be opened in excel and will have all the acquired data. However, it will store the original data only; since you wan to to store the processed data, you can find this article useful.

[Hamed26]

Thanks a lot.
Unfortunately, The answer is not noticeably changing by using X4 or X2 or X1 decoding type, just slightly changing but still far away from its correct answer . Errror percentage is about 2142757.423 % !!!!! a disaster !!! It should show about 1500 rpm while it shows between 0.07 to 0.09 rpm !!!

And about the data points, I see the data from the waveform graph showing Angular velocity Rad/s, it has only 4 data points (I am not talking about the rpm indicator). Still the same problem. I am so baffled. 

[Cavarval]

Hamad,

I am not talking about the RMP indicator either, but the Waveform Graphs, including the Velocity Rad/s one.

About the decoding type, did you try the two pulse method? If you have a two pulse encoder and you use the X1, X2 or X4 methods you will have wrong readings.

[Hamed26]

Thanks for your answer.
This is my encoder ( please have a look at the attachment file). I have both A & B channels. 

Should I deactivate the Z index Enable button?

Another question is why the following method of speed measuremnt working correctly for me but the buffered counter method is not working?

Measure Angular Position and Velocity with a Single Counter and no External Clock

As stated before, what I really need is a reliable method for measuring angular velocity with a deterministic approach such that I can define sampling rate and samples to read in order to synchronize them with other measurement tasks.  

Thanks.

[KeaneSenses]

Were you able to try to track a and b from the encoder as a two pulse encoder?