This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

  • TI Thinks Resolved

Input 4/20mA / 0/10V

Intellectual 400 points

Replies: 25

Views: 9205

Hi everybody,

I'm looking for a solution of my problem, but I cannot find any answers by myself so I'm requesting your help.

For our new product, we'll develop an analog input module (as we can find with PLC...). Our module will be able to do 0/10V and 4/20mA. For the moment, I have three terminals for each input (One for Voltage input +, one for current input +, and for input - ). My problem is that I would to do the conversion of 0/10V o 4/20mA to 3V3 without any selection switch (especially to include or not the shunt resistor used to convert 4/20mA).

You'll find my diagram in enclosed documents. If you have any suggestion to improve it, I'll be very happy.

Thank you in advance,

Best regards,

Fabrice

DIAGRAM.pdf

  • Hello Fabrice,

    We've worked on other designs similar to this one and the overall design method is valid.  Consider putting your design into TINA-TI SPICE to test the behavior and adjust the gain / scaling if required.  Also, we created a similar design that you may find interesting:  TIPD195 - 3-Terminal PLC Input reference design.   

    Regards,
    Collin Wells
    Precision ADC Applications

  • In reply to Collin Wells:

    Hi Collin,

    Thank you for your diagram. I'll look it, and ask you if I have some questions.

    Best regards,

    Fabrice

  • In reply to fabricepeden:

    Hi Collin,

    I just look your design, it's very interesting but I think some points will be very difficult for us.

    On my module, there will be 8 channels, INA188 has only one channel, so I will need 8 INA188, but is there another reference which can has more channels (2 or 4) ?

    Moreover, in this design, INA188 is supplied with + or - 15V, is it compulsory to do that, because the output voltage is between 0.2 and 4.8V, so is it possible to supply it between 0 and 3V3 ? Then, my µc accepts voltage up to 3V3, so I think I need to recalculate resistors to adap the output voltage and also the power supply.

    For example, I can put Vref at 1.66V and output voltage can be between 0.2 and 3.1V, do you think it's possible ? Because I'm trying to simulate it with TINA-TI, but 1,66V is for 0V and not for 5V. So, it means that my input will be between 0 and 10V.

    Thank you in advance,

    Best regards,

    Fabrice Péden
  • In reply to fabricepeden:

    Hello Fabrice,

    The INA188 will not work with a +3.3V supply.  Consider using the INA333.  You can modify the TINA files associated with TIPD195 to use the INA333 and the different voltage scaling ratios that you determined using the equations from the design guide.

    Regards,
    Collin Wells
    Precision ADC Applications

  • In reply to Collin Wells:

    Hello Collin,

    Thank you for this information.

    I'm trying to do that. To simulate the INA333, I have just to modify the value of resistor of INA188 (150k instead of 20k and 50k instead of 25k) ? Or I need to modify another thing ?

    Thank you in advance,

    Regards,

    Fabrice Péden
  • In reply to fabricepeden:

    Attach your simulation file and we'll take a look. Depending on your configuration the input common-mode voltage vs. output voltage may limit the output voltage swing when operating on a 0/+3.3V supply. We'll take a look once we see the circuit.

    Regards,
    Collin Wells
    Precision ADC Applications

  • In reply to Collin Wells:

    Hello Collin,

    Thank you for your help, I'm also discovering TINA-TI software ;-)

    I have found INA333 in the library, but can I use the same formula than in the TIPD195 document ?

    Regards,

    Fabrice Péden

    TIPD195_functional_with_INA333.TSC

  • In reply to fabricepeden:

    Hello Collin,

    I'have try to recalculate values of resistors.

    R1 = 100k

    R2 = ((R1*Vd)/(Vin-Vd)) = ((100k * 400mV)/(10 - 400mV)) = 4.167k

    G = ((Vout - Vref)/(Vd)) = (3.1 - 1.67)/(400mV)) = 3.575

    GINA333 = 100k/(3.575-1) = 39k

    But with these values, I haven't the wished curbe. For me, I'd like to have : Input : 0V --> 0.24V & 10V --> 3.1V

    Regards,

    Fabrice

    8664.TIPD195_functional_with_INA333.TSC

  • In reply to fabricepeden:

    Hello,

    Looks like you're getting closer.  Could you share an image of the circuit results you're getting as well as the desired results?  It was a little unclear in your last message. 

    For example: 

    Input = 0-10V

    Output = ?

    Input = 0-20mA

    Output = ?

    Regards,
    Collin Wells
    Precision ADC Applications

  • In reply to Collin Wells:

    Hello Collin,

    Sorry for my unclear message. Please, find below :

    - My design

    - result for 0/10v

    - result for 4/20mA

    Regards,

    Fabrice Péden

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.