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RCV420 Test configuration

Anne Garafalo62
Prodigy 50 points
Other Parts Discussed in Thread: RCV420

Hello, 

I need to design a circuit to test the RCV420 with different input currents (within the 4-20mA range).  I am not sure whether the RCV420 is designed to connect to active or passive sensors.  If I put a resistor with the correct resistance between -In and +In, would the circuit create a loop current?  Or does the component connected to -In and I+n have to be active and thus must be powered by another voltage source?

Thank you,

Anne 

  • 0
    TI__Guru 63965 points

    Hello,

    The RCV420 does not provide a power source for your 2-wire (or 3-wire) sensor transmitter.  As shown in Figures 8 and 9, the same positive power-supply used for the RCV420 is commonly used to power the sensor transmitter circuitry.  In addition to a positive power supply, the RCV420 also requires a negative supply voltage for proper operation.

  • 0 in reply to Collin Wells
    Prodigy 50 points
    Thanks for the quick response! I am making a current source which will connect to -In and +In. If the load resistance between -In and +in is too high then the current source will no longer be constant as it will be affected by the load resistance (which is the input resistance from the RCV420). From the schematic of the RCV420 on page 1 of its datasheet, it looks like most of the voltage in the loop will drop across the 2 75ohm resistors. In that case I would not have to worry about the input resistance as it would be very low. Is that correct?

    Thank you again
  • 0 in reply to Anne Garafalo62
    TI__Guru 63965 points

    Hi Anne,

    That is correct.  Most loop transmitters can support resistances up to 800Ohms, which is much higher than what the 2x75Ohm resistors inside the RCV420 will add to the loop.