frequency response - sound and vibration

[samtha]

Hi,

I need to find the frequency response of the DUT. I am using the NI example from sound and vibration toolkit to do

so (LabVIEW 8.5\examples\Sound and Vibration\Getting Started\SVXMPL_Getting Started with Swept Sine (DAQmx).vi) now my problem is

to tabulate the phase difference between the stimulus and response when i do it i get constant values. Even though i dont give any response 

signal to the channel i get the wave same as stimulus, is it suppose to be like that !!!!!!!!!! I will attach my vi so that it gives the idea where 

i am measuring the phase difference pls check it and help me with this.....thank you in advance.

[samtha]

Hi can anyone pls help me out with my problem its urgent!!!!!!!!!!!!!!!!!!

[Jason_D]

sk_labview,

Do you get good results when you run the original example?

If not it is likely that your stimulus is not being input the way you think.  Can you test the cards you are using in MAX to verify the input?

If you are getting good results with the original example it must be something you modified.  Are you getting good results on the graph?  What about the log file?  Are they both showing the same bad results?

[samtha]

May be you are right it must something i modified even i thought the same thing i will trial and test everything and get back to you thank

you for the reply.....

[samtha]

Hi i get error at swept sine engine function the error is:

 Error -200018 occurred at SVT Swept Sine Engine (DAQmx).vi:1DAQmx Write (Analog 1D DBL 1Chan NSamp).vi:1

Possible reason(s):

Measurements: DAC conversion attempted before data to be converted was available.

Decrease the output frequency to increase the period between DAC conversions, or reduce the size of your output buffer in order to write

data more often. If you are using an external clock, check  your signal for the presence of noise or glitches.

 I found it by highlighting the execution of the program, I am not able to figure out what to do.......so can you please help me out

with this !!!!!!!!!!!!!!!!

[sundarganesh]

What is the DAQ card you are using for executing this Frequency Response?

This DAQ error is related to the output frequency of your signal higher than the possible output rate of the card. Basically, you are trying to update at a rate higher than the capability of the card.

For doing Frequency response, generally you need to have a NI DSA card (446x/447x/449x) with one Analog output and two analog inputs (minimum). Generate the swept sine signal from the Analog output channel, give this signal as input to your DUT and also to one of the Analog input channel. This input to your Analog input channel will act as your Reference signal. Then the response signal from your DUT, connect it to another Analog input channel. You would get a very good response results.

The reason why you need to have a DSA board is that, for doing Frequency response, we need to acquire both high frequency and low frequency components without much loss. This is possible only if your DAQ board has a higher dB value (in the range of >110dB) which is present only in DSA boards.

I have completed a Frequency Response Analysis just a week back with the same example programs. So there wont be any problem with that vi.

Regards,

Sundar Ganesh

[samtha]

hi Sunder thank you for your response the daq card iam using is USB 6215 or i even have USB 6221 but i am using 6215 so is it possible to

determine the frequency response using this DAQ  

[sundarganesh]

NO.

You cannot use a M Series DAQ card for doing Frequency Response Analysis. You need a Simultaneous Sampling DAQ card like 6133 or DSA cards which are also Simultaneous sampliing card.

The reason is, all the M Series DAQ cards has only one ADC which is used for all the input channels through Multiplexing. This configuration cannot be used for Frequency Response as we have to sample both the source and the response signals at the same time which is possible by having individual ADCs for individual channels. This configuration is present in S Series DAQ cards and DSA cards.

Regards,

Sundar Ganesh

[samtha]

hi sundar thank you again i have one question since we dont have dsa boards or 6213 daq card, can we use 2 daq cards daq card 6221

to generate and the other daq card 6215 to acquire the response......is it possible that way.....

[Jason_D]

sk_labview,

You absolutely can use an M-Series card to run this example (I just used my PCI-6251).  It may not perform as well without DSA and as the text on the example mentions you will want to seriously consider out-of-band aliasing.  If you don't believe me you can look at the list of supported devices for this example.

That being said which device did you get the error with?  What frequency were you trying?

If you could you should try the defaults.  Also you might want to give the example, Getting Started with Swept Sine Express VI a try.