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RCV420: RCV240 OUTPUT 1-5V for 4-20 mA

richard bouvier
Prodigy 40 points
Part Number: RCV420

Good morning all,
I want to use a RCV420 chip to manage a 4-20 mA line,
except error on my part, the output signal goes from 0 to 5v for an input of 4 to 20 mA,
is it possible to have an output that goes from 1 to 5 v for an input of 4 to 20 mA?
because with a 0-5v output, if the line is broken the output signal will be 0v and it will not be possible to do the break detection.
Thanks for clarifying the point to me.

  • 0
    TI__Guru 54576 points

    Hi Richard,

    Yes, it is possible to configure the RCV240 to produce a 1V - 5V output for a 4-20mA input.

    The Vout/Iin required is Vout/Iin = 5V/20mA=0.25-V/mA.

     Using the equation below from datasheet; we can set the gain to 0.25-V/mA:

     

     

    Let Vout/Iin = 0.250V/mA, Rs=75-Ohms and solve for RX

     Rx = (.250/.3125*Rs)/ (1-(0.250/0.3125))

    Rx  300-ohm

    Connect REF_IN of “T” network (pin12) to GND (no offset injection required, unless you wish to correct any small offset error internal to RCV420 device). 

     The device will produce a 1-V to 5-V output for a 4mA to 20mA input current connected as below, with external resistors, RX1 = RX2 =300-ohms.

    Please see diagram below,

    Thank you and Best Regards,

    Luis

     

  • 0 in reply to Luis Chioye
    Prodigy 40 points

    Thank you very much Luis,


    (my notions of electronics are more than 20 years old ....
    and sometimes, I get lost in the datasheets of the different components),
    by rereading the datasheets following your answer, I found all these indications of modifications that you explain to me.
    like what, taking the time to read ....

    I drew, using several examples of basic applications, on datasheets.
    I want to have reliable measurement channels,
    that's why I'm not content with a simple 250-ohm resistor, however, given the cost of the components, if I can avoid wasting money unnecessarily.
    (It's a personal montage)

    could you tell me if the drawing is good?
    or if there are errors or bad designs?


    thank you

  • 0 in reply to richard bouvier
    TI__Guru 54576 points

    HI Richard,

    I will close this E2E thread and continue the discussion on the new thread below.

    http://e2e.ti.com/support/amplifiers/f/14/p/841541/3113656#3113656

    Many Thanks,

    Kind Regards,

    Luis