Resynchronisation between NI9215 and NI9263 after filtering

[MathieuSG]

Hello,

I just bought a NI system with a NI9172, a NI9233 for acoustic and vibration measurement with IEPE conditionning and AC mode, and a 9215 to have voltage Inputs.

I also have Labview 8.5 pro, and the sound & vibration toolbox 5.. I am a beginner with Labview.

The 9215 is used to measure electret microphones (used in mobile phones) with a swept sine measurement. I have to filter DC offset, because there is no AC mode with the 9215.

I have 2 questions.

1) Synchronisation between 9215 and 9263

If I do a loop between Output and Input (Fs = 50kHz, number of samples = 25000, sinus at 1kHz), I observe a delay around 0,47164 second, so 23582 samples. 

Where does this delay come from ? By reading the data sheet, the delay of ADC is around 4.4useconds so much smaller than what I measure. I suppose that my VI is not very good concerning synchronisation. I also tried to measure delay by using the VI SVL Measure Propagation Delay (DAQmx).vi with a smooth pulse, and the result is 1 sample at 50kHz. I find this more realistic. So, how can I have a good synchronisation in my VI ?

2) DC filtering of the 9215

I designed a high pass filter (RIF), and it causes an other delay. For my swept sine analysis, I need a good synchronisation between output and inputs. I found an VI express which perform such measurement. I can precise how big is the delay (number of samples) between the 2 channels. So, I need to correct this value with the delay introduced by my RIF filter, is it right ?

The next step is to use a speaker to generate the swept sinus, so I suppose I will have to use the SVL Measure Propagation Delay (DAQmx).vi with a MLS to measure the acoustic delay between mic and speaker. Is it the good way ?

Could you help me and correct me if I am in the wrong way ?

Thanks for your advices.

Mathieu 

[ElRambo]

Hello,

I have a few questions for you :

When you say that you're connecting an output to an input, between which hardware's output and which hardware's input do you do that ?

When you say that there is a delay, what do you mean ? How do you get this delay ?

Moreover, a RIF filter can add a small delay for sure.

Regards,

[MathieuSG]

Hello,

thanks for your help. In fact, I wanted to send you my VI in order to explain more precisely my problem, but I modified it...

I made an other one which can explain what I would like to do with some comments on the front panel. As you will see, I am Labview beginner...:) I suppose my problem is that the tasks made by Outputs and Inputs do not begin simultaneously...

"between which hardware's output and which hardware's input do you do that"

My hardware's output is NI9263 (4 analog outputs). My hardware's input is NI9215 BNC (4 analog input with BNC). I send

The Output AO1 is direct linked to the AI0.

 After all this pre-processing (downsampling, highpass filtering), I would like to do swept sine measurement. I suppose that synchronisation is very important for such measurements. I saw in the Swept Sine VI Express (sound and vibration toolbox) that I can include a delay in samples. Must I add here the delay due to highpass filtering ? Or modify settling parameters and/or integration time ??

If you have some advices to help me !!  Thanks

Mathieu

[ElRambo]

Hello Mathieu !

I had a look at your VI and I have some advices for you :

Have you ever heard about triggering ? In your case that would be the solution to synchronize your generation and acquisition, I advise you to have a look at software triggering. In LabVIEW you will find loads of examples with the example Finder (Help > Example finder).

Moreover, when programming with DAQ, I advise you not to use the DAQ Assistant which is pretty useful to test something fastly but it's not really efficient. As you are begginer with DAQmx, you can simply right click the DAQ Assistant and select "Generate DAQmx code" that will show you the way to develop your own code with DAQmx VIs.

Hope this helps ! Don't hesitate to ask again if you need help !

Have a nice day !

Regards,

Message Edité par Maxime MULLER le 09-12-2008 02:58 AM

[MathieuSG]

Hi Maxime,

thanks for your answer.You are right.

I have ever heard about triggering, because I already used other acoustic software measurement, and for me it was only to start a measurement (with an external signal for example).

I didn't know that I had to define trigger between hardware output and input, but it 's logical.In the other softwares I used, it should have an internal trigger, but I could not see it. With Labview I have to make this function.

I will try your advices. At the moment, I just uses VIs express in order to understand how Labview works, but I clearly see that I 'll have to perform VIs myself.

Thanks a lot. 

Mathieu

[MathieuSG]

Hello,

I read a lot of documents concerning Timing and Triggering on the NI website.

I improved but I have difficulty to understand how define sample clock, and number of samples, between read and write tasks...

For example, on the attached VI concerning finite sampling acquisition, it doesn't work. I generate a 500Hz sinus(1000 samples at 50kHz as excitation signal) and I meet an error concerning buffer size, or sample clock.... How should I configure these parameters ?

Furthermore, I saw that in NI examples, a Triggering VI is used. I didn't use it because I read that I could configure the Timing VI of the Input task with an internal trigger linked to the output task. Is it a good way or is it better to use triggering VI ?

Thanks for your advices.

Mathieu