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XTR117: Current loop Circuit accuracy.

Sebastian P J
Expert 1775 points
Part Number: XTR117

Hello,

I am designed a current loop circuit using XTR117, for connecting PH sensor. I am attaching the schematics of this circuit.

Here Two precision trimmers are used one is used for bias control and the other is used for gain control. This circuit is working from the loop power supplied from the ADC circuit followed by this circuit.

I am using high precision resistors in this circuit. The ADC reads the current across a 49.9R resistor.

Advice me to get maximum accuracy and 4-20mA precise output.

Regards 

Sebastian

  • 0
    TI__Mastermind 23050 points

    Sebastian,

    A few things:

    1) One thing you need to make sure of is that the IRET ground is common to your input circuitry and not shared by other grounds in your system (like the supply ground). This node must be allowed to float to maintain proper regulation. Additionally, you will want to ensure that the total current consumed by all of your input circuitry does not exceed 4mA. The XTR cannot regulate to a current level below what the input circuitry requires.

    2) You may consider using a more precise external reference to set your input offset current. The integrated reference drifts 0.1mV/degC and is not as precise over temperature as a dedicated reference would be.

    3) You may also consider adding some filtering to the feedback of U1B to cut down on some of the noise into the XTR117. Just keep in mind that since you are adjusting the gain with a potentiometer you will also be moving the cutoff frequency.

    4) If you want to get an estimate for what kind of error you could expect, you may find some of the tabs in the following spreadsheet useful: DAC+XTR_2WIRE_XMITTER_ErrorCalcs_kd.xlsx