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Original question:

XTR117 with 0-3.3V from DAC?

XTR117: 4-20mA to 0-3.3V converter

Neel Shah101618
Intellectual 550 points
Part Number: XTR117
Other Parts Discussed in Thread: XTR115, XTR116, PGA309, PGA308, XTR105, TLV333, ADS7042, ADS7142

Dear E2E Team,

We are trying to convert a 4-20mA temperature transducer to a 0-3.3V signal. I believe we cannot use the XTR117 for the same purpose and the first thing that comes to mind is simply to use a variable resistor to read the voltage across the resistor.

We tried that but it is quite painful to tune all the potentiometers to work accurately since we need 8 such potentiometers for every device.

Is there a solution to this challenge?

Further we want to read this data after a ADC conversion into the I2C or the SPI bus of the micro-controller.

What is the best solution for this project?

- Ambimat Team

  • 0
    TI__Guru 54356 points

    Hello Neel,

    -What type of current transmitter is required? 2-wire or 3-wire?

    -What type of temperature transducer are you using (RTD, thermistor, thermocouple)?

    -Are you referring to an ADC with I2C or SPI interface on the receiver side? 

    The XTR115, XTR116, XTR117 are two wire current transmitters, they accept a current input and produce a 4-20mA current output.It is possible to interface a resistive temperature sensor such as a thermistor or RTD with an instrumentation amplifier with the XTR115/6/7 to produce a 4-20mA output; but will likely require an instrumentation amplifier and front-end calibration/adjustment to obtain the 0-3.3V signal.

    If using a bridge sensor, the PGA308 or PGA309 are programmable gain amplifiers that offer offset and gain digital calibration and can be interfaced with the XTR115,6,7 two-wire current transmitters. 

    In addition, the XTR105 which is a 2-wire current transmitter that can be interfaced directly with RTDs and includes the RTD excitation current sources, instrumentation amplifier and current output transmitter.  A reference design example using the XTR105 measuring an RTD is below:

    www.ti.com/.../TIPD161

    For more information on 2-wire or 3-wire current transmitters and reference designs, you can review the links below.

    https://e2e.ti.com/support/amplifiers/f/14/t/945188

    Regards,

    Luis

  • 0 in reply to Luis Chioye
    TI__Guru 54356 points

    Hello Neel,

    Please clarify:

    Are you concerned with interfacing a temperature sensor with the two wire 4-20mA current output transmitter (such as the XTR117)?

    Or are you interested in converting a 4-20mA current signal into a 0-3.3V voltage for an ADC on the receiver side.

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Intellectual 550 points

    Luis Chioye said:

    Or are you interested in converting a 4-20mA current signal into a 0-3.3V voltage for an ADC on the receiver side.

    This is my interest.

    Thank you for taking the time to understand our query.

    Let me know the most optimal way of doing that?

    - Ambimat

  • 0 in reply to Neel Shah101618
    Guru 140200 points

    Hi Ambimat,

    a simple resistor with an OPAmp buffer will do. The rest can be done in the microcontroller :-)

    Kai

  • 0 in reply to kai klaas69
    Guru 140200 points

    Or do it this way:

    ambimat_4m_20m.TSC

    Kai

  • 0 in reply to kai klaas69
    TI__Guru 54356 points

    Hi Ambimat,

    There are many ways to accomplish this. 

    Attached is an example similar to Kai's example, using the low cost, low power, compact, precision TLV333 op-amp.

    The circuit powers up with a +3.3V unipolar supply, receives a 4mA to 20mA input into the load resistor and produces a ~99mV to 3.18V output into a single ended ADC.  It could drive a standard single-ended, SAR ADC at moderate sampling rates.

    For example the ADS7142 is a single-ended input, +3.3V supply, 12-Bit SAR ADC (806uV resolution) with I2C interface in a compact QFN QFN 1.5mm x 2.00mm package.  Alternatively, the ADS7042 is a single-ended, +3.3V supply 12-Bit SAR ADC with SPI interface. The TLV333 amplifier can drive this particular SAR ADC at about 100kSPS max sampling rate.

    Thank you and Regards,

    Luis 

    forum_1-5-20_tlv333.TSC