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Original question:

[FAQ] How to Select Amplifiers for 4-20mA Field Transmitter Applications

INA181: suitable for Loop Current ?

Jhon Jairo Zambrano
Prodigy 80 points
Part Number: INA181


Hi,

Best Regards.

I'm thinking of using the INA181 to convert a 4-20mA signal with an Rshunt of 3 ohms. This will result in a Voutput of 1.49V - 2.45V.

I would like to know if the INA181 is suitable for this purpose. Additionally, the idea is to have the PCB support 2-Wire (Loop current), 3-Wire, and 4-Wire connections. However, in the INA181 datasheet, I found the following information:

The 2, 3, and 4-wire connections look as follow:

In each scheme, my host board will provide power to the transmitter device.

Thanks in advance.

  • 0
    TI__Mastermind 32395 points

    Hello Valued Engineer,

    The relevant specification to determine possible use with these Cases is the device's operational Vcm (common-mode voltage) range. The input Vcm at INA181 input pins is essentially system ground for the first two connections.

    In the 4-wire connection, Vcm will float to the Transmitter's output voltage. I do not know what this is. However, as long as Vcm is within the tested specified limits (0V to 26V), then accuracy and performance will remain in specification.

    Note the survivable limits are -0.3V to 26V.

    There will be some input offset error with a change in in DC Vcm, but it should not be unacceptable. the input referred offset error term is: Vos_cmrr = |12V-Vcm|*10^(-84dB/20).

    I hope this helps clear up some things.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    Prodigy 80 points

    Hi Best regards

    Its a drawing mistake, the Rshunt is always referenced to Ground. The host board power supply the transmitter

  • 0 in reply to Jhon Jairo Zambrano
    TI__Mastermind 32395 points

    Hey Jhon,

    I see. Ground reference shunts are perfectly fine. The only concern is if the Vcm could ever fall below -0.3V and potentially damage the device. As long as this is not a possibility, then the design is valid.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    Prodigy 80 points

    In which case the VCM could fall below -0.3V. Our power supply always be single power supply

  • +1 in reply to Jhon Jairo Zambrano
    TI__Mastermind 32395 points

    Hey Jhon,

    The most common reasons the Vcm at low side shunt may drop below -0.3V are due to inductive kickback when rapidly switching on/off loads or user error with a reverse polarity power connection. These may not be relevant to you system/application, but it always good to know.

    Sincerely,

    Peter