120v.ac to mv/ma

Discussion in 'General Electronics Chat' started by DaveT, Oct 25, 2007.

  1. DaveT

    Thread Starter New Member

    Oct 25, 2007
    Is there a method to obtain a 4-20ma / 1-5mv output from a 120v.ac line?
    I heard somewhere about putting a resisitor in the 120v line?
    Would like to have specifics on this matter.
  2. techroomt

    Senior Member

    May 19, 2004
    first a 4 - 20 ma (1 - 5 vdc) is a conrol signal used to represent an analog value of something, e.g. water pressure, temp, etc.. you can install a resistor, usually 250 ohm to switch back and forth from 4 - 20 ma and 1 - 5 vdc. converting 120 vac power, normally a supply voltage, would do well to power a dc power supply for that control signal system, with more devices to do the controlling. otherwise, no.
  3. niftydog

    Active Member

    Jun 13, 2007
    It's recommended that you avoid direct connection to the mains voltage wherever possible. In this case, a simple 5VDC power supply will get you most of the way there. To work out the rest you need to decide whether you need the current loop (4-10mA) OR the control voltage (1-5VDC) to control whatever it is you're controlling.