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  • chithrachennai

    Member • Aug 7, 2013

    sir ,

    once i was asked in an interview why the industrial standards are 4-20 mA for current , voltage 0-30 V (i am not sure about voltage standard)?

    can you please explain this concept

    thanks in advance .
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  • Jeffrey Arulraj

    Member • Aug 7, 2013

    Sub 1W criteria will be met in those condition for sure

    And also most electronic Component operate in the 0 to 30 V region with about 20mA current through them
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  • Ramani Aswath

    Member • Aug 7, 2013

    chithrachennai
    once i was asked in an interview why the industrial standards are 4-20 mA for current , voltage 0-30 V (i am not sure about voltage standard)? can you please explain this concept
    The advantage of a current loop is that the resistance of the connecting leads especially over long signal transmission lines does not affect analog signals. The electronics will adjust the voltage to ensure that the analog signal retains the accuracy. In an industrial environment with varying electro-magnetic loads, current loops have very good reliability.
    The 4ma zero value has a bonus in that it tells if there is a break in the leads.
    Here is a good article on current loops from National Instruments:
    #-Link-Snipped-#

    A voltage analog output has to be used with a high impedance measuring circuit.
    I do not know why 0-30V is specified. If I may hazard a guess the higher voltage is likely to be more accurate than millivolt signals because of lead impedance.
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  • Surya Neo

    Member • Aug 10, 2013

    thanks
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