4-20ma Current Loop Assistance

Discussion in 'The Projects Forum' started by george789, Mar 22, 2008.

  1. george789

    Thread Starter New Member

    Mar 22, 2008
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    I Need a 4-20mA Generator as well, but I could not use anything from above.
    Is there a specific circuit with components i can find to make a portable insrument of calibration, using a 9V battery?
    thanx in advance
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    It is best if you post your own thread rather than attach your post to an active or in this case a dormant post. By doing so you will enhance the prospects for a solution that is more likely to fit your unique requirements. Also it will avoid any confusion between your request for help and that of the existing poster. This is particularly true in cases where the existing post is currently active.

    Welcome to All About Circuits. We sincerely hope you are able to derive benefits from this forum and we look forward to your future participation.

    hgmjr (moderator)
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    So, you just need a variable 4mA-20mA source using a 9V battery?

    Go to National Semiconductor's website:
    http://www.national.com
    and search for LM317L. Download the datasheet, and look on page 9.
    There are two current limiter circuits shown near the bottom left of the page, one a simple adjustable current limiter, and the other a precision current limiter.

    In the simple adjustable current limiter schematic:
    A 240 Ohm resistance between the OUT and ADJ terminals will give you ~5mA output from the ADJ terminal.
    A 60 Ohm resistance between the OUT and ADJ terminals will give you ~20mA output from the ADJ terminal.

    Unfortunately, the LM317L requires a minimum of 5mA of current flow in order to properly regulate. If you really need to get down to 4mA, you'll need to look at a different regulator.
     
  4. george789

    Thread Starter New Member

    Mar 22, 2008
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    I am very sorry for improper use but I descovered this site two hours ago so I am not familiar hgmjr.I'll try to learn the rules.I have been once in Tennessee.
    Thanx for your suggestion SgtWookie.This device should be 4-20mA exactly because it is supposed to be a calibrating instrument (Marine Machinery Automation)
    Important values is 4 - 12 - 20mA as it means low - med - high values.
    Thank you once again for answering. I am George from Hellas (Greece)
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    No need to be sorry. You are not the first new member to this forum to make that error. It was obvious that the post was not intended to disrupt the existing post.

    I think you will enjoy your interactions in this forum and I see that you have alreedy begun to receive some helpful advice from our members.

    I would also recommend that you explore the AAC ebook at www.allaboutcircuits.com. It is a one-of-a-kind resource for information that will come in very handy if your goal is to learn more about the fascinating world of Electronics.

    Please visit us as often as you like.

    Good Luck,
    hgmjr

    PS. I do hope you enjoyed your visit to Tennessee.
     
  6. Pich

    Active Member

    Mar 11, 2008
    119
    4
    Good quality current sorces for calibration can be very expenensive because of the accurecy and stability needed to calibrate field intruments. Most calibrators these days are microprocessor based with a analog output.
    That being said, if you are willing to tacke it this could be an iteresting project and can be done in the old fashion analog way. Look at the LM10 this IC can be used as the core for the calibrator. This link as probably all the info you need http://delabs.tripod.com/cirdir/analog.html
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Ahh, I see. Well, my suggestion will not be nearly accurate enough for your purposes.

    Attempting to design a calibration instrument is not a trivial task, and just the components themselves will be very expensive. They usually have internal temperature controls to minimize drift, compensation for component aging, require a minimum on-time of an hour or more before use, etc. - and even then, they still require bi-annual or annual calibration.

    I am not optimistic in your chances of success to develop such a calibration source which is powered soley by a 9v transistor battery. There simply will not be enough current available to stabilize temperatures before the battery is dead.
     
  8. george789

    Thread Starter New Member

    Mar 22, 2008
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    Well battery's power is not to heat anything.4-20mA will replace for example a water level transmitter output which is sending information to a water level controller (We talk about marine auxiliary Boiler).Or it can replace the 4-20mA output command signal of the water level controller, to the water valve positioner.It is just a 4-20 mA generator with low consuption.I had one but they lost my luggage in the airport of Spain.A mA-meter is connected in line so everytime mA is shown.
    I thank you so much for your interest, and forgive my English I know they are not so good.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Well, if you're going to be using a mA meter in series with the source, it can simply be a variable current source.

    The LM317 needs to have 10mA current passing through it in order to guarantee regulation. This could be handled by an additional current divider network for ranges below 10mA.

    I suggest the LM317 since they're so easy to get. However, if you can get a TL431 or TL432, a more efficient circuit could be designed.

    See the attached for a dual-range low current supply built around an LM317.
     
  10. george789

    Thread Starter New Member

    Mar 22, 2008
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    I am gratefull StgWookie. I'll give it flesh n blood tomorrow morning.
    Have a nice day.
    Greetings from Hellas (Greece).
     
  11. george789

    Thread Starter New Member

    Mar 22, 2008
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    I am grateful StgWookie. I'll give it flesh n blood tomorrow morning.
    Greetings from Hellas (Greece) & have a nice day.
     
  12. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I PM'ed StgWookie about this, but he didn't reply. I don't think the low range is constant current, independent of load resistance. If you try it, let us know how it works.
     
  13. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Well, I just reread the entire thread, and I feel pretty stupid, as I should. :(
    I see that george789 does not need a true current source, because he has a meter in series. I had seen that previously, but the significance escaped me.
    My apologies to SgtWookie and george789.
     
  14. cornevanbeem

    New Member

    Nov 19, 2008
    1
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    try this "XTR110" search for the datasheet and find out>>>>>
    cvb from the netherlands.
     
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