homemade 4-20 mA/0-10VDC source
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  1. #1
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    Confused homemade 4-20 mA/0-10VDC source

    Has anybody out there ever built a homemade 4-20mA/0-10VDC source with two 9V batteries, a 5K pot, and a 500 ohm resistor? The pot and resistor would be 5W.

    Or maybe I shoud use three batterys?
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  2. #2
    Join Date
    Jun 2009
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    StL, MO
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    Sure. Two batteries will be fine unless you plan on 4-20mA through a 1000 ohm load. The following version has a few more components that extend battery life and limit maximum current and voltage.
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    UA LU 562

  3. #3
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    What is the intended purpose of this source? Do you intend to use it as a permanent input to a device or do you want to use it to test things on a bench or in the field?

  4. #4
    Join Date
    Nov 2008
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    The next step up is to use a 12v lantern battery 'cause 20 mA from a 9v battery is a little high.

    For 50 cents more, op amps would really be a step up. Their output voltage won't change with varying loads.

    What is the minimum/maximum load resistance you reasonably want to drive? How much current is necessary at 10 vdc? Will 5% accuracy be enough? You want the thing to have it's own meters? What temp. range must the thing work in? How fast must the current/voltage change?

  5. #5
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    Quote Originally Posted by WhoIsThat? View Post
    For 50 cents more, op amps would really be a step up. Their output voltage won't change with varying loads.
    What do you mean by op amps?
    "It's not that I'm smart, it's that I stay with the problem longer”
    Albert Einstein

  6. #6
    Join Date
    Sep 2007
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    SoCal
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    Operational Amplifier

    I assume that is what he is referring to.

  7. #7
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    I like to tinker but

    you can buy a Analog Signal Generator (ASG) from Kele for a couple hundred bucks. The Evile Empire sells a nice one for about twice that.

  8. #8
    Join Date
    Nov 2008
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    Operational amplifier it is
    http://www.national.com/mpf/LM/LM324.html#Overview
    These things are dirt cheap nowadays.

    And these
    http://www.datasheetcatalog.org/data...wn/mXqxxqx.pdf

    Do you want to run your source off house current or only batteries?

  9. #9
    Join Date
    Sep 2009
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    Midwest
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    33
    If you are calibrating and need precision, go with Fluke 705 Loop Calibrator.

    http://us.fluke.com/usen/Products/Fl...(FlukeProducts)

  10. #10
    Join Date
    Nov 2008
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    Quote Originally Posted by 24vac View Post
    If you are calibrating and need precision, go with Fluke 705 Loop Calibrator.

    http://us.fluke.com/usen/Products/Fl...(FlukeProducts)
    From this link it seems your circuit battery should be at least 28vdc.
    If this thing is $600 and you spend a morning making your own from $10 in parts, you've paid yourself. . .let's see. . .per hour. . .hmmm. . .

  11. #11
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    Western Wa
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    Just a bench test or field calibration source. For setting up 4-20mA and 0-10, or 2-10VDC stuff. Any ideas or op-amp circuits would be great. Not sure if I want to go AC power or not, but that wouldn't be a bad idea. I would just use my other meters to measure with.

    Thanks to all.
    God Bless our Veterans

    God Bless the USA

  12. #12
    Join Date
    Nov 2008
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    1,673
    Quote Originally Posted by Randy S. View Post
    Just a bench test or field calibration source. For setting up 4-20mA and 0-10, or 2-10VDC stuff. Any ideas or op-amp circuits would be great. Not sure if I want to go AC power or not, but that wouldn't be a bad idea. I would just use my other meters to measure with.

    Thanks to all.
    If you just need the endpoints, 4.00 mA and 20.00 mA and 0v and 10.00v, it's easier. Would you also need midpoints [12.00 mA and 5.00 v]?

    You want to go that way?

  13. #13
    Join Date
    Apr 2004
    Posts
    566
    http://www.johnsoncontrols.com/publi.../sysa350p.html

    buy one of these off e-bay the work well as a simulator just replace the temp sensor with a fixed resistor (500 or 1000 i belive)

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