(DAQmx) Reading Circular Disc Profile Using Eddy Current Probe.

[AtulS]

Hello Every one,

I want to setup a DAQmx voltage task to read Circular Disc profile using eddy current probe.

Disc is rotating at 200 RPM scanning every row. (Plz Refer attached image )

eddy current probe is shifting to next row after completing one rotation (360 Degree) till last row .(Total number of rows are 32) For Every row circumference is reducing.

I reading data for complete single row when i get trigger for one rotation is complete using DAQmx Read function.

But at the end after collecting all Rows data i m getting array size different for each row 

i have kept 

Continues Sample with Multiple Channels

Sample Clock Rate = 10000 and Samples = 5000

and For Read Function No Samples = (-1) kept floating (Which is in while loop) i m taking data out from Read pallet when i get one rotation is complete trigger (Used Case Structure) 

I m plotting this Data to Intensity Graph but due to change in array size for every cycle defect position also gets changed . i m plotting it to the 0 -360 Degree range

I would like to know what Design pattern should i used and Sampling Rate and No. of Samples . 

[GerdW]

Hi AtulS,

use an encoder to provide a certain number of pulses per rotation.

Use those pulses to externally trigger your ADC sample clock.

Then you get the same number of samples per rotation!

(And even better: then those samples will be distributed equally with respect to rotation angle - and not in time like you do right now!)

[AtulS]

Time taken to complete one rotation for Disc is 240 ms is constant for all rows i m

reading data from Read function after every 240 ms for 32 rows.

Externally Trigger ADC Clock means i have to create another task to read no. of encoder pulses and apply those triggers to Sample clock function.

plz correct me if i m wrong i don't have much knowledge  about this.

 is there any other way bcz i don't have Encoder to test it out.

[GerdW]

Hi AtulS,

Externally Trigger ADC Clock means i have to create another task to read no. of encoder pulses and apply those triggers to Sample clock function.

To "externally trigger ADC clock" means you need DAQ hardware supporting external sample clocks.

You don't need any additional task. All you need then is to tell the current DAQmx task to use the external sample clock: there is a "source" input at DAQmxTiming function…

plz  …  bcz

Please read this! 🙂

[AtulS]

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@GerdW wrote:

Hi AtulS,

Externally Trigger ADC Clock means i have to create another task to read no. of encoder pulses and apply those triggers to Sample clock function.

To "externally trigger ADC clock" means you need DAQ hardware supporting external sample clocks.

You don't need any additional task. All you need then is to tell the current DAQmx task to use the external sample clock: there is a "source" input at DAQmxTiming function…

plz  …  bcz

Please read this! 🙂

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Thanks for your Reply.

I am using NI-6220 Card to read Eddy current Probe voltage  and Trigger for one complete rotation.

Is there any other possible solution Except Encoder.  

[GerdW · Accepted solution]

Hi AtulS,

I am using NI-6220 Card

It supports also external AI sample clocks (as well as other kind of triggers).

to read Eddy current Probe voltage  and Trigger for one complete rotation.

So you could use this trigger as a start trigger for the AI task: when a new revolution starts the AI task is starting to take samples. You could maybe also use it as stop trigger to stop the AI task after the revolution is complete…

Is there any other possible solution Except Encoder.

An encoder would be the most accurate option as it would allow angle-based measurements independent from rotation speed deviations! Check your requirements before deciding which hardware to use…

[AtulS]

to read Eddy current Probe voltage  and Trigger for one complete rotation.

So you could use this trigger as a start trigger for the AI task: when a new revolution starts the AI task is starting to take samples. You could maybe also use it as stop trigger to stop the AI task after the revolution is complete…

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Thanks For Reply.

Start and stop position is same for one revolution how do i integrate this logic for multiple rows.

is it possible to you post some VI snippet so i can refer.