Actions
Forum Thread Details
  • Replies 9 replies
  • Subscribers 395 subscribers
  • Views 4703 views
  • Users 0 members are here
Related

How o measure 4-20 mA Current

oksbwn

I need to measure 4-20mA current output from some sensors. How can i do that ? Currently i use resistive drop to get the analog voltage and provide that to ADC of the controller. Are their any current input ADC ?

Parents

  • 4-20mA is a nice standard for instrumentation measurement and is used in industry extensively. the nice thing about it is it has automatic fault detections as zero = 4mA, any less than 4 means an error, more than 20 also an error. being a current loop also means impervious to alot of noise sources and also lead length can be significant subject to the ability of the source to provide enough volts. It can even be measured by many series devices... anyway I digress (I spent many years in the Gas industry using 4-20mA transducers for pressure, flow and temperature.

     

    Your current approach has been the mainstay for what seems forever. Use a resistor to measure the current (IE, convert the current to a voltage), typically a 200Ohm or 250Ohm is used to then provide a 5V FSD,but of course if your measurement device is only able to handle a lower voltage, reduce the sense resistor appropriately.

     

    I am not aware of any current input ADC, those that claim to support 4-20mA are basically providing the current sense resistor themselves so you're no better off except for perhaps a lower BOM or board footprint.

Reply

  • 4-20mA is a nice standard for instrumentation measurement and is used in industry extensively. the nice thing about it is it has automatic fault detections as zero = 4mA, any less than 4 means an error, more than 20 also an error. being a current loop also means impervious to alot of noise sources and also lead length can be significant subject to the ability of the source to provide enough volts. It can even be measured by many series devices... anyway I digress (I spent many years in the Gas industry using 4-20mA transducers for pressure, flow and temperature.

     

    Your current approach has been the mainstay for what seems forever. Use a resistor to measure the current (IE, convert the current to a voltage), typically a 200Ohm or 250Ohm is used to then provide a 5V FSD,but of course if your measurement device is only able to handle a lower voltage, reduce the sense resistor appropriately.

     

    I am not aware of any current input ADC, those that claim to support 4-20mA are basically providing the current sense resistor themselves so you're no better off except for perhaps a lower BOM or board footprint.

Children