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designing a DAQ

Discussion in 'Embedded' started by kkrish, Dec 6, 2009.

  1. kkrish

    kkrish Guest

    Hi all,
    I have to design a data acquisition system for two different
    signals. One is within the frequency range 300 hz (+ or - 25 Hz) and
    the other one is less than 5 Hz. I do not know the amplitude ranges of
    these frequencies(I guess it may depend on the sensors used). I do not
    know how to select the sensors and how to design the other hardware.
    If you can either give a pointer to me or if you could tell me what
    are the dos and dont's and the important things to consider while
    designing. Can I design a single daq card that can capture the 300Hz
    and 5 Hz signals. I just know that I need to use a D/A converter and a
    signal conditioning (amplifier and filter) circuit. How to proceed.
    Are there any proper commercial techniques related to DAQ design? I
    have collected some data from some micrcontroller project sites but I
    am seeing some expert comments or suggestions being passed in this
    group and I want to get some suggestions.

    Thanks in advance.
    kkrish, Dec 6, 2009
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  2. The design depends on your exact requirements.
    There are many processors/controllers that have support for
    multilpe DACs. Else, you can use a single DAC that can have multiple
    channels. There are many opensource tools like COMEDI are very
    famous in DAQ world. Further, RTlinux also supports COMEDI.

    Karthik Balaguru
    karthikbalaguru, Dec 6, 2009
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  3. The first thing you should research is the difference between a
    D/A converter (DAC) and an A/D converter (ADC). If you are acquiring
    data, you need an A/D converter.

    The next thing you need to do is get firm specififications on the
    input signals and sensors. Without those specifications you
    will have a tough time designing a good system.

    A good place to start would be the National Instruments web
    sit, www.ni.com. They've been in the PC data acquisition
    business about as long as there have been PCs. I'm sure they
    have notes and white papers on the general process of
    data acquisition.

    Mark Borgerson
    Mark Borgerson, Dec 6, 2009
  4. kkrish

    larwe Guest

    Well, maybe, but he said DAQ - Data AcQuisition, not DAC.
    larwe, Dec 6, 2009
  5. What he said was:

    " I just know that I need to use a D/A converter and a
    signal conditioning (amplifier and filter) circuit. "

    Mark Borgerson
    Mark Borgerson, Dec 7, 2009
  6. LOL! I pointed out National Instruments, because they're NOT a
    competitor of mine---at least not until they can put together
    a system that runs on 15mA and will fit inside a 3" ID pressure

    Thanks for seconding my opinion. The OP does have some basic
    research to do. If he wants more help, we'll need more
    information on the system requirements.

    Mark Borgerson
    Mark Borgerson, Dec 8, 2009
  7. kkrish

    kkrish Guest

    Hi all,
    Thanks for your replies.
    you are right, I wrote it as DAC but actually I meant A/D and thanks
    for pointing out the mistake.
    What are the other information you need? I do not know if the sensor
    and sensor connectors I am going to use is a low capacitance or high
    capacitance because I do not know what type of sensor I need to
    choose. I am going to measure rotational force. Specifically I am
    going to measure the amplitude and phase difference of two rotating
    forces with a pair of sensors. As of now I assume noise level of the
    surroundings is negligible(Of course I have a filter) and I do not
    worry about the bandwidth now. I saw some application notes from IC
    manufacturers and NI website(after you said) and I understand
    something about what is DAQ but I still need help related to component
    selection and hardware.

    Thanks in advance.
    kkrish, Dec 8, 2009
  8. kkrish

    linnix Guest

    What frequencies? How do you know that you need analog sensors? It
    depends on how you pickup the signals. Your first task is to figure
    out the sensors.
    linnix, Dec 8, 2009
  9. kkrish

    kkrish Guest

    Hi all,
    Thanks for your replies.
    Yes, I am trying to measure torque on a shaft, and I also have find to
    the amount of force or vibration on the body containing the shaft when
    the shaft rotates.
    kkrish, Dec 10, 2009
  10. kkrish

    linnix Guest

    Couple of 3D accelerometers should do it. One stationary for
    vibrations and one for rotations.
    linnix, Dec 10, 2009
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