Current measuring ic

Discussion in 'The Projects Forum' started by kripa, Jan 4, 2012.

  1. kripa

    Thread Starter New Member

    Jan 4, 2012
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    I NEED AN CURRENT MEASURING IC HAVING RANGE 0-8 MICROAMPERE.. CAN ANYONE HELP ME??
    :confused::confused::confused::confused:
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I believe Texas instruments had such a device. I ordered some samples but I cannot seem to remember the part no. It is a little chip with a shunt and converter built into it.

    I need to check my stock to find it.
     
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  3. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    You can do this with a good CMOS op-amp with femtoamp input bias current. A problem you will run into is noise...you have a finite number of electrons to measure, and they will produce "shot" noise which occurs due to the randomness of moving electrons. The amount of noise is proportional to the square root of the number of electrons.

    You can reduce the noise by low pass filtering, though this will decrease the bandwidth (increase the settling time) of your measurement. How fast do you need to measure the current, and at what resolution?

    One excellent way to get good resolution and low noise is to integrate the current into a small cap for a fixed period of time. You can complement this by de-integrating with a known fixed current (to eliminate inaccuracies caused by variations in the capacitor).

    Such a circuit can be implemented with a PIC micro with built-in comparator, voltage reference, and internal RS latch (along with a good low input bias current op-amp).

    Regardless of the method you choose, you will need "guard rings" around your sensitive (high impedance) conductors. Otherwise, leakage currents (due to contamination and humidity) will destroy your measurements.
     
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  4. wayneh

    Expert

    Sep 9, 2010
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    Last time I looked for such a thing, I narrowed my search to the LMC6035 or LMC660.
     
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  5. russpatterson

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    Feb 1, 2010
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  6. joeyd999

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    Jun 6, 2011
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    Ummm.....sensitivity of 65 to 185mV/A is a little low for his application...
     
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  7. kripa

    Thread Starter New Member

    Jan 4, 2012
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    sir,
    cud u jus look 2 ur stocks and get me the result pls..
     
  8. R!f@@

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    Apr 2, 2009
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    If you are referring to me, I need a little time.
     
  9. joeyd999

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    Jun 6, 2011
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    ?????????? (needed 10 to post this reply)
     
  10. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Are you in a hurry? Measuring such current pecisely is nothing simple, so you need to be more patient, also making other threads on the same topic will just make others loose interest in your problem.

    Please use proper English and ask questions that are easy to understand. Also don´t expect others to reply on the same day, we got our jobs and stuff and do this only because we want to.
     
  11. kripa

    Thread Starter New Member

    Jan 4, 2012
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    sorry sir.. i'm new to this.. i'm in a hurry as i need to complete a project work within a 30 days deadline.. i need to sense a current and need to interface it to the radiosonde..
     
  12. kubeek

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    Sep 20, 2005
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    You could maybe start by telling us what is a radiosonde and what interface it has.
     
  13. kripa

    Thread Starter New Member

    Jan 4, 2012
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    A radiosonde (Sonde is French for probe) is a unit for use in weather balloons that measures various atmospheric parameters and transmits them to a fixed receiver. Radiosondes may operate at a radio frequency of 403 MHz or 1680 MHz and both types may be adjusted slightly higher or lower as required. A rawinsonde is a radiosonde that is designed to only measure wind speed and direction. Colloquially, rawinsondes are usually referred to as radiosondes.. sir, i think we can interface it using PCI or an I2C..
     
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