Filtering my displacement signal

[Ryan_V[DE]]

krithika,

Are you seeing the same thing on the oscilloscope as in your LabVIEW program? If so, you'll need to figure out how to clean up your signal before it gets to your DAQ card. Also, does a higher sampling rate give you a better quality signal?

Regards,

[krithika]

Hi Ryan

What i see when i run the attached VI and look at the acquired data at 100 Hz i see that was able to see a sinusiodal waveform with distortion. But at 10 Hz the acquired sine wave is really clear.

I have attached my how my output looks like on labview.

I tried increasing the scan rate of analog input but no luck!

Pls Help Me Out!

Thanks

Best
Krithika

[krithika]

Hi Dev

Thanks for the post and VI. I am actually having trouble visualizing the displacement signal (the acquired signal).

I have attached my output how it looks like at 10 Hz and at 100 Hz.

I want to see a sinusoidal acquired data- the waveform chart on the left!

Pls help me out!

Thank You

Best 
Krithika 

[krithika]

Hi

I have an idea but i need your help for the same.

I have a VI attached. Its not a working VI, but hope that will convey my idea.

As for the descrition:

All this while when i was acquiring the data from my SCXI i entered ob0! sc1! md1 ! 0:1. But as i want to view the output from channel one alone i changed it to ob0! sc1! md1 ! 1.

Now the signal looks more distorted. I figured that with there is noise in my acquired data even when i don't feed in my sine wave. So I want to first substract the Analog input (when no sine wave is fed) from its self so that i can avoid the noise in the first place. After i have done that i want to execute my Vi and acquire my signal.

So sort of a closed loop. But i have no idea how i combine them together.

I Need YOUR SUGGESTION and HELP.

Pls let me know if this idea is feasible???!!
Have a Great Weekend.

Best Regards

Krithika

[devchander]

Hi Krithika,

Had a look at ur VI and Doc.

Try this, Keep sampling rate of AI and number of samples to read equal. A

nd try sampling at 1itself( since it satisfies Nyquist criteria for measuring a 100 Hz signal)

also run it at sampling rate = number of samples to read = 10K, and see if it works.

Plus, it looks your Test circuit that takes excitation from AO and is measured on AI is also doing some some attenuation. am i right?

Because in 10 Hz snapshot you have sent, I observe your AO generates 1V amplitude signal, whereas your AI measures it as  1mV amplitude signal.

So , can u suspect that this circuit has some components which are passing 10 Hz but stopping the 100 Hz signal?

regards

Dev

[devchander]

Hi Krithika,

Had a look at the Vi that u plan to use for noise subtraction.

Looks like this is what you want to do.

First Performing a Finite acq  without excitation, and then subtract this value from all acquired values(with excitation)

This is fine if you want to cancel off an initial 'offset' in your measurements,

but not to cancel out noise.

This is what i suggest, try to determine, what the noise is, where it is originating from and then take action on removing this.

Regards

Dev

[Ryan_V[DE]]

Krithika,

It sounds to me like the problem with your application lies outside of the computer. Please give us a list of your hardware and connections. Also, please let us know the input and output signals, both expected and observed values (amplitude, frequency, shape, etc.). This will allow us to determine what is causing the behavior you are observing.

Regards,

[krithika]

Thanks You!!

As for the Hardware Specs - I am using a CB-68LP for my analog output from the DAQ ( SINE WAVE GENERATION). I am using SCXI 1321 for my ANALOG input. The analog input is from a strain gauges mounted in a motor.

I send the sine wave analog output to an amplifier that conditions the signal  and i feed that signal to a dc motor (Electrodynamic vibration generator)  that has an attachment on to which i have strain gauges mounted (full bridge config). So the conditioned sine wave fed into the motor produces displacement which is I can obtain from the strain gauges mounted on the motor.

I have attached  tha picture that might help visualize. So at different frequencies the displacement will be different in amplitude but I should be able to get a sine wave.

The freq ranges i want to work on is from 10 Hz to about 1000 Hz.  I have maintained the Analog output from the DAQ - amplitude of the signal to be 1 v p-p.

The daq board is RT series PCI 7030/6040 E . So traditional DAQ.

Also i tried taking FFT of my signal i am having trouble displaying it. I can see the numbers but when i want to display the same its not happening. I have that VI aswell.  Pls Let me know if i am missing some thing??!!

Thank you Ryan and Dev for all the help !!

I have attached the motor specs aswell. Hope i was able to give you enough information.

Best

Krithika

[Ryan_V[DE]]

Krithika,

What SCXI module are you using? The 1321 is only a terminal block which allows you to make connections to external signals. The 1321 should be mounted to a module inside the SCXI chassis. Please let us know this module number.

Thanks,

[krithika]

The chassis is SCXI 1000. And then i have SCXI 1321 plugged into 1121.

Thanks

Krithika