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  1. #1
    Join Date
    Jan 2015
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    64
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    voltage drop 4-20mA loop powered device

    Its been way too long since electronics class. Can anyone tell me if I am on track or not??

    Does anyone know whats the maximum distance I can get a can power up a transducer with 24vDC and receive a mA signal back for a DDC input? I was curious if anyone would know a voltage drop formula that I could use to see what my maximum wire length could be...

    The max current draw of the Veris transducer is 29mA and I dont know what the resistance would be for 500' of 18 or 16 gauge cable calculate total resistance.


    Something I found online, voltage drop equals 2 x i x L x R x t / 1000

    Where I=current, L=length in Meters, R is the Resistance of the conductor, t is a temperature correction factor

    So 24vDC/.029 Amps = 828 ohms using ohms law

    (2 x .029 x 152.4 (feet to meters) x 828) / 1000

    =7.31 volt drop

  2. #2
    Join Date
    Jan 2003
    Location
    USA
    Posts
    2,423
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    Your off in the weeds.

    >So 24vDC/.029 Amps = 828 ohms using ohms law

    That would be the resistance of the total circuit, including the sensor. Your formula needs ohms/m of the wire I'm assuming.

    I wouldn't even bother doing the math unless your going to exceed thousands of feet. I can't ever remember having an issue with voltage drop on 4-20ma.

    http://www.kele.com/templates/content.aspx?id=4716
    Propagating the formula. http://www.noagendashow.com/

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