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Manual 4-20mA Offset Circuit using RCV420 and XTR110

Chris Littlewood
Prodigy 10 points
Other Parts Discussed in Thread: XTR110, RCV420

The purpose of this circuit is to provide some form of manual offset for a 4-20mA driven gauge connected directly to a sensor. A 1-turn offset potentiometer (R1 on the XTR110) is intended to be panel mounted next to the gauge for easy adjustment.  I have the following questions before building the circuit.

 

                -Is the negative voltage on Pin 4 of the RCV420 absolutely necessary or can the IC function properly with only positive voltage connected to Pin 16?

 

                -Figures 5 & 6 of the XTR110 data sheet show information for a 0-10V In to 4-20mA Out circuit. The resistor values for a 0-10V In circuit are R1=100KΩ, R2=100KΩ, R3=49.9KΩ, R4=36.1Ω. Will these resistors be adequate for 0-5V In? If not, what values are recommended?


                -An MTP50P03HDL transistor is planned for use on the XTR110. Since VCC will be 12-15 VDC, 12-15 VDC will be applied to the transistor source via Pin 1. This transistor has a drain-source voltage of 30V and wonder if it will be adequate, and if not, is there a better recommendation?

 

Thanks and appreciate any assistance available.

 

 

 

  • 0
    TI__Mastermind 27715 points

    Hello Chris,

    I apologize for the delay in getting a response to your post. Do the same questions you had on November 13th still apply?

    Best regards,
    Ian Williams

  • 0 in reply to Ian Williams
    Guru 21975 points

    Chris,

    Answering your questions in your first post:

    A negative supply is required on the RCV420 to allow output voltage swing to 0V.

    Values of the trim components do not need to be changed when the input is configured for 0 to 5V input.

    A 30V rating on the output transistor should be adequate for your application.

    Regards, Bruce.