PXI-4462 - Microphone Set Up

[MeCoOp]

First time using NI-DAQmx, PXI-4462 and microphones.  Setting up a task in Max and I'm unsure as to what type of analog input to select: voltage or sound pressure.  Not sure what type, if any corrections are done by the 4462.  Tried several searches but unable to really find any info.  Any help is much appreciated.....MeCoOp

[Nick_F1]

Hi MeCoOp,

Thank you for posting on the National Instruments forums.

When creating a task in MAX, if you use sound pressure, it is applying a scale factor for you.  It can output the data in dB’s.  If you want to use voltage and apply the scale factor yourself, then you will want to use Custom Voltage with Excitation since your microphone will most likely need some sort of excitation to work.

If you have any other questions, please let me know.

[MeCoOp]

Well if you insist......My chassis has the PXI 8185 controller.  Can I connect the 8185 directly to my laptop and communicate with the hardware through LabVIEW?  I would like to be able to test my software/hardware interface before making an executable.

Thanks.

[Nick_F1]

Hi MeCoOp,

If you want to interface with the hardware in our PXI chassis, you will need to get something like the NI PXI-ExpressCard 8360.

You can also use remote desktop or something similar like VNC to control your 8185 with your laptop.  Neither one of these programs are supported by NI, but there should be a lot of help on the internet to show you how to control a computer with another computer using either remote desktop or VNC.

The other option is to look at this knowledge base article.
Remote Laptop Control of PXI System

I’m not exactly sure what you are trying to do, so I’ve listed several options for you.

[MeCoOp]

I've been having trouble building confidence with my results thus far.  I wrote a simple vi to read from the 4462 and analyze the data.  Currently I have two microphones set up in the reverberant room connected to the 4462.  The problem I encounter is no matter what channel I select, meaning regardless if the channel has a microphone hooked up or not, the output in the form of total band power is the same.  To futher illustrate my test set up I am using a pre-polarized PCB condenser microphone model 377B20 and a PCB microphone pre-amp model 426A11.  I've also attached the simple read program that is giving me the aforementioned results.

Thanks in advance.

[Nick_F1]

Hi MeCoOp,

If you have the Sound and Vibration Measurement Suite or the Sound and Vibration Toolkit, you can open and run the SVXMPL_Baseband FFT(DAQmx).vi or SVXMPL_Zoom FFT (DAQmx).vi.  By using these VI's, we can figure out if there is an issue with your application or your hardware since we know that the examples work with your 6642. 

To find the example, click on Help >> Find Examples...
Then go to the folder Toolkits and Modules >> Sound and Vibration >> Analyzing and Processing Signals >> Frequency (FFT) Measurements

Give this a try and let me know what happens.

[MeCoOp]

Nick, thanks for the timely response.  I tried using the SVXMPL_Baseband FFT(DAQmx).vi  and the SVXMPL_Sound Level Meter(DAQmx).vi with the same results from my previous post.  Independent of the channel having a microphone connected my readings tend to be the same.  I'm not sure what else to try but I am begining to suspect a hardware issue.

[Nick_F1]

Hi MeCoOp,

Would you happen to have a signal generator around that you can send a sine wave to the DSA card with?  That is one way to check to see if your hardware is working correctly.  Another issue might be that your condensor mic might not have power.  The preamp will amplify the signal, but the microphone itself will need power in order to work. 

[MeCoOp]

Nick,

I don't have anything availible to generate a signal.  The microphone is powered through the IEPE sent from the 4462.

[Jordan_D]

Hi MeCoOp,

Do you have a power supply or any other known signal source that you can use to test out your analog inputs? This would allow us to verify that your DSA board's analog inputs are functioning properly before looking to elsewhere to solve the problem.