Shop OBEX P1 Docs P2 Docs Learn Events
4-20ma signal — Parallax Forums

4-20ma signal

geneshultsgeneshults Posts: 22
edited 2011-01-15 18:09 in BASIC Stamp
Hello to all.
I was wondering if there maybe a way, the BS2 can process a 4-20 ma signal from a device that is powered from a 24vdc source? I have a few devices that are powered from a 24vdc source and want to use with my BS2.

Thanks
Gene

Comments

  • LeonLeon Posts: 7,620
    edited 2011-01-15 08:28
    Use a suitable interface chip (ADI makes them) and an ADC.
  • stamptrolstamptrol Posts: 1,731
    edited 2011-01-15 11:04
    You can also build a very cheap interface with a TIL111 or H11a optocoupler, capacitor and the RCTIME commmand.

    The 4-20 mA goes through the optocoupler's LED and the transistor output changes the effective resistance of the pot in the RCTIME circuit.

    The response is not linear but is very repeatable.

    Cheers,
  • $WMc%$WMc% Posts: 1,884
    edited 2011-01-15 18:09
    geneshults wrote: »
    Hello to all.
    I was wondering if there maybe a way, the BS2 can process a 4-20 ma signal from a device that is powered from a 24vdc source? I have a few devices that are powered from a 24vdc source and want to use with my BS2.

    Thanks
    Gene
    '
    If you put a 250 ohm resistor in series with the 4-20ma loop, Then read the voltage across the 250 ohm resistor you will read this.
    '
    4ma = 1 volts
    8ma = 2 volts
    12ma = 3 volts
    16ma = 4 volts
    20ma = 5 volts
    '
    This can be read through an ADC0831 or eq. analog to digital converter.
    '
    Take a look in StampWorks pg. 156 for some circuit info and code (replace the pot. with the 250resistor NO Vdd connection)
    http://www.parallax.com/Portals/0/Downloads/docs/books/sw/Web-SW-v2.1.pdf
    '
    '~~~~~~~~~~~~~~~~~~~~~~250ohm~~~~~~~~~~~~~~~~~~~~
    ++++24volts
    x---/\/\/\/\/\--x
    load/transmitter/inputcard/etc.
    4 to20ma Loop
    neg24volts
    ' read voltage here > ______^_1 to 5 v _^
Sign In or Register to comment.