Data Acqusition Using NI PCI 4474 and Dayton EMM-6 Condenser Microphone

[xcnmoore]

Hi all,

Before I take the plunge and purchase the NI PCI 4474 for data aqcuisition in my system, I'd like to verify a few points.

• Will the 4474 accept a signal from a 48V Phantom Power supply that has been unbalanced by way of a XLR to SMB adapter?  Is this DAQ card a good idea for a condenser microphone? 
• If I had issues with ghosting when I used a different DAQ that had multiplexing, is this card likely to solve the ghosting problem? I think the ghosting appeared because the output impedance of the Phantom Power supply seemed high when measured: 10k ohms.
  • Note: I need to sample from multiple channels at once because the other two channels give the power input to my acoustic transducer (a speaker, not the microphone) by way of a current and voltage measurement. The source impedance of these other two channels are around 1 ohm and 50 ohms.
• The rated 102.4 kS/s rate will apply to all three channels at once, correct?
• In figure 7 on this page (http://www.ni.com/white-paper/7059/en/#toc5), for a pre-polarized set-up (the EMM-6 microphone is pre-polarized, I think), I can't tell what all the components are...could someone tell me? The caption could have listed what the purpose of each component was, specifically the third.
  • Is the Dayton EMM-6 pre-polarized or externally polarized? It says it is an electret condenser, so I believe it is pre-polarized, but would like to verify.
    • If it is, should the built-in excitation current be set to 0 amps?
• Would purchasing the 4474 from ebay be a poor decision?

Sorry for the large list, but I want to be sure.

Thank you in advance!

[RahRahMirez]

Hi xcnmoore,

So I have a few clarifying questions that will help me better understand what kind of device you need, and if the NI PCI-4474 is right for your application.

1.  First, this particular card is not spec'd to take inputs of greater than 42.4V.  Are you actually reading in this phantom power voltage?  I see in the spec's for the microphone you mentioned that it utilized phantom power between 15V and 48V.  Are you certain you'll be needing to read 48V?

2.  The speaker you are powering:  what kind of power does it require?  And you intending to generate power from the card to power the speaker, correct?

3.  The sample rate would be applicable to each of the channels.  You can know this because the specifications manual says the spec's are for "simultaneously sampled" channels:

http://www.ni.com/pdf/manuals/373861d.pdf

4.  The components you're seeing are the microphone on the left, then the corresponding preamplifier, then the ancillary equipment for reading that signal.

5.  I can't really speak to the Dayton microphone spec's, sorry.  You may want to check with them to verify.

6.  I've heard on multiple occaisions of people getting counterfeit devices on the internet that do not work with National Instruments products and drivers, so you do take an inherent risk when purchasing a card on the internet that it is genuine hardware.  My personal advice would be to consider purchasing a device and therefore be certain your hardware will be functional.