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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,
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 WellsPrecision ADC Applications
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In reply to Collin Wells:
Thank you for your diagram. I'll look it, and ask you if I have some questions.
In reply to fabricepeden:
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.
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 ?
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
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.
Input = 0-10V
Output = ?
Input = 0-20mA
Sorry for my unclear message. Please, find below :
- My design
- result for 0/10v
- result for 4/20mA
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