Filtering my displacement signal

[krithika]

Hello All

I want to say that this discussion forum really increases my confidence to work on LABVIEW. I am really new to LABVIEW and i have posted so many silly questions and have got really helpful answers.

Well but i still have more unanswered question that i need help with.

So far I am able to send run a motor using sine wave input. Also i am able to get the displacement measure from the strains on the motor and visualize the same on LABVIEW(front panel).

Question 1:

I am displaying the sine wave in a wave form graph and i get the displacement output on a transposed waveform graph. How can i put them both in one graph?

Question 2:

My displacement is a sine wave but it has some noise. I want to filter the same. I am attaching with this email how my output looks like. Can you pls suggest me the best way to filter out the signal.

Question 3:

My acquired displacement data is continuous, if i want to check point by point what do i need to add in?

Also i have a traditional DAQ (RT series: PCI 7030- 6040E) board.

I really need all the help and support from you guys.

Thanks for the quick and helpful suggestions.

Best

Krithika

[krithika]

I am sorry i forgot to attach the document.

This post has it! PLS HELP ME OUT!

[devchander]

Hi Krithika,

for Q1: Modify the attached VI for your application and use it.

It performs simultaneous Ai/ AO and so, you will have better synchronisation.

In the same vi, i have inserted the generated signal array into the acquired signal array ands so you will get them on same graph.

For Q2: for filtering, use any software filter provided in labview.Just study the characterstic of your noise and use a suitable filter.Find this in functions-> analyse-> signal processing -> filters.

Q3 : for point by point analysis i suggest you write data into a file and do analysis offline !

Note: i advise you to do filtering on saved data instead of filtering during acquisition because since filtering also takes up process time and might affect your acquisition/generation.

But if you do not get any acq buffer related problems, go ahead and perform filtering during acquisition itself.

regards

Dev

[krithika]

Hi Dev

Thank you so much for the quick response. I am looking at the AI-AO Vi  that you sent me and I guess will contact you if i have some questions. But I have one other question.

If you see the output that i sent you-  I am not able to visualize the sine (diplacement ) at higher freq, say 100 HZ. Fro my application i need to play around with the Frequency ( range 1 HZ to about 100 HZ) and view the displacement on LABVIEW in real time.

So i will need to add the filter during data acquistion. I wanted to first subtract both the signals ( generated sine wave and the diaplacement) and see how different they are and view it on a graph. But as my diaplaced signal is a trasponsed array i am having difficulties with it.

Pls give me your suggestions.

Thank you so much once again for all the help so far.

Best Regards

Krithika

[devchander]

Hi Krithika,

Correct me if i understood you wrongly. When you said  "i am not able to visualize the sine (diplacement ) at higher freq, say 100 HZ." do u mean, that you are not able to generate a sine of 100 HZ??

If its so, you should be able to achieve this by selecting suitable buffer size, cycles per buffer and update rate.(buffer size= 10000, cycles /buffer 100 and updater rate 10000) and this should give you this desired sine wave of 100 hz.

regards

Dev

[krithika]

Hi Dev

No what i mean is that the noise in my displacement signal is high. I did not mean to the generated sine wave using labview but the analog input sine wave (from the strain gauges on my motor).

Thanks

Krithika

[Ryan_V[DE]]

Krithika,

From your attachment, it looks like your problem is not noise, but rather attenuation of some sort. Do you have any external (hardware) filters which have a bandwidth less than 100Hz? Are you able to see this 100Hz sinusoid with some other instrument (oscilloscope, RMS DMM)? Finally, are you sure that you are not eliminating the signal in software?

Regards,

[krithika]

Dear Dev

Thanks for the Suggestion. I did what you said and the sine wave looks great. But i am having trouble when i got to higher frequencies. With 10 Hz the output looks great. But at say 100 HZ i am not able to see the sine wave (Analog Input- The acquired data ) at all.

Pls help me out.

I have attached my VI with this email.

Best Regards

Krithika

[krithika]

Hi Ryan

Thanks for the email. I did try to look at the acquired signal at 100 Hz using an Oscilloscope i can see the sine wave but its distorted.

No i don't have access to hardware filters.

I have posted the updated VI , what Dev had suggested and i am able to see a better Sine wave at 10 Hz but no luck at higher frequency.

PLS HELP ME OUT.

Thanks

Best
krithika

[devchander]

Hi Krithika,

In your Attached VI, For AO write, i made update rate as 10000, Buffer size as 10000 and cycles per buffer as 100

And i got a 100 Hz signal of quite good resolution.

I have made vasues defaut in ur VI tha ti have attached, so run it and check it out.

Regards,

Dev