Converter 0-25V AC signal into 0-10V DC or 4-20mA

Discussion in 'General Electronics Chat' started by kavula, Dec 20, 2004.

  1. kavula

    Thread Starter New Member

    Dec 20, 2004
    Dear All,
    I am looking for 0-25v AC signal into 0-10V DC and 4-20mA signal converter circuit/IC.
    This is for monitoring 24V AC voltage from PLC. My PLC will accept inputs only either 0-10VDC or 4-20mA signal.

    Please help me!

  2. beenthere

    Retired Moderator

    Apr 20, 2004

    Use a bridge to rectify your AC. Add a small filter capacitor - 4.7 uF or so - and put the DC voltage through a 20K pot to ground. Adjust the wiper to give 10VDC when the input is 24VAC. The DC voltage will always be in directr proportion to the AC voltage input.
  3. Xray

    Well-Known Member

    Nov 21, 2004

    Beenthere has a good circuit to provide a simple direct conversion of the AC voltage range to the DC monitoring voltage range. But the problem with that setup is there is no built-in safety that would let the PLC know if a monitoring signal wire should break. In other words, if a wire should break, the PLC would sense ZERO volts, which is a valid reading! It would "think" that the 24vac supply is intentionally putting out zero volts. That's where the beauty of the 4-20mA signal comes into play. 4-20mA is an industrial standard for monitoring sensors, and as interconnecting analog signals between equipment. In the above application, 0 vac would give 4mA current, and 24vac would give 20mA current. If the 4-20mA signal wire should break, the PLC would know that zero mA is a fault condition. It would output an Alarm condition (flash a red light or ring a bell, etc.). There are many 4-20mA converter modules on the market that provide monitoring many different voltage polarities and ranges.