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Hi there,can we can just discuss about low cost solutions for generating 4-20 ma current?

coolbox

Hi there,

 

4-20 ma is standard for data acquisition from sensors in industrial environment.There are are many techniques like PWM and DAC for 4-20 ma current generation.But still i want to hear from automation experts for options about generating 4-20 ma.Is any micro controller which can directly output 4-20ma?

Parents

  • Thanks Peter and john for your valuable answer.

    Being specific,here actually i am referring to Electrical programmable transducers.In which we presents electrical quantities such as voltage,current,active power,reactive power,frequency,phase angle in form of either current or voltage.so can you suggest some solution in which I can integrate both voltage output and current output on single channel.

    Also I want add that although 4 mA is  lowest point. some times you need to provide 0-20 mA range for some quantities.

    electrical programmable transducers follows IEC 60668 standards.

     

    parth pandya

Reply

  • Thanks Peter and john for your valuable answer.

    Being specific,here actually i am referring to Electrical programmable transducers.In which we presents electrical quantities such as voltage,current,active power,reactive power,frequency,phase angle in form of either current or voltage.so can you suggest some solution in which I can integrate both voltage output and current output on single channel.

    Also I want add that although 4 mA is  lowest point. some times you need to provide 0-20 mA range for some quantities.

    electrical programmable transducers follows IEC 60668 standards.

     

    parth pandya

Children
  • in reply to coolbox

    Unless a device has independent power it is will not support  the current going to 0 as some of that 4mA is actually used to power the electronics at the sensor end and in some industrial environments there are devices called “Intrinsically safe Barriers“ or “Zener barriers” that is used to limit the power available to a sensor in for example a gas prone environment.

     

    See this PDF, it has a nice schematic of such a barrier http://www.mpelectronics.com/pdf/app_note_for_stahl_barrier.pdf

     

    Typically the 4-20mA loop is sourced from a 24V supply (In the safe zone) as is the supply typical for most industrial instruments

     

     

     

    So as I said, going to zero is not normally an option and going below 4mA is typically taken as a fault condition

     

     

     

    Like everything, there are always exceptions to this (uPower sensors running from a coin cell for years and sealed in an explosion proof housing for instance) that would not require power from the 4-20mA loop to power the sensor but this still does not allow for the common understanding that below 4mA is typical of a fault condition and to choose otherwise would limit the use of the solution

     

     

     

    Hope this helps

     

     

     

    Peter