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Thread: 4-20mA Input Cards

  1. #1
    Join Date
    Mar 2013

    4-20mA Input Cards

    I am looking at some 4-20mA Wago analog input cards. They have 2 varieties, and I am not sure of when to use one version over the other.

    One version has 0V ran from the analog input card to the sensor, and then returns back to the input on the analog input card.

    The other version runs 24V out to the sensor from the analog input card, and then returns back to the input:

    Struggling to find some traction on deciding when to use one over the other. I understand "single ended", but both are single-ended....when would one use the 24V version and when to use the 0V version?
    Time is of the essence, and I am low on essence. ~ Graham Hill

  2. #2
    Join Date
    Aug 2010
    What is your 4-20mA transmitter (sensor, transducer,... field device that sends 4-20mA signal)? If it is 4 wire then you need 4 wire card otherwise the single ended.

    4 wire transmitter: power +, power-, signal+,signal-
    Transmitter gets power (power+/-) from an source and sends out 4-20mA signal to the analog input card.

    single ended (2 wire transmitter): power+, signal-
    Transmitter gets (+) power and sends 4-20mA to analog input card (+). Analog input (-) is connected to (-) of power supply.
    "Because it's there!"
    George Mallory

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