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.

  • Resolved

INA125: INA125P giving a different reference voltage than what is being given in the data sheet

Part Number: INA125

For the last six months, I have been using INA 125 P amplifier. The problem I am facing is that in figure 6, page number 13 in the datasheet, pins 14 and 4 have been connected and due to this connection, we would be getting a reference voltage of 2.5V (as is shown in the figure). Experimentally, I also made the same connection but I am getting a reference voltage of 1.44V. Why this anomaly is happening when everything is correct in my circuit? Please help.

  • Hello,

    Please post a copy of your schematic for us to diagnose the issue.

    Regards,

    Zak Kaye
    Precision Amplifiers Applications 

  • In reply to Zak Kaye:

    Hello Zak,

    I am attaching the schematic herewith

    I have exactly made these connections. But my problem is that in the highlighted regions, I am getting a voltage of 1.44V instead of 2.5 volt. Pins 12,3 have been connected to the ground of the Wheatstone bridge. And at pin 1, I am supplying a voltage of 5V as is given in the data sheet. Pin 2 has been connected to pin 1.

    My problem is that I want to get 2.5 V as the voltage which excites the Wheatstone bridge.

    Regards,

    Captain

  • In reply to CAPTAIN SWING:

  • In reply to CAPTAIN SWING:

    Zak,
    I am uploading the schematic diagram but on posting, the diagram is not coming. I tried a couple of times. So, can you give your mail id so that I can mail you straight away the diagram. If not, can you suggest some other means?

    Saurav
  • In reply to CAPTAIN SWING:

  • In reply to CAPTAIN SWING:

    Zak,
    This time it has come. I hope my problem is much more comprehend-able now.

    Captain
  • In reply to CAPTAIN SWING:

    Hi,

    What is the resistance of your bridge? If you disconnect the bridge do you see the expected 2.5V output?

    Regards,

    Zak Kaye
    Precision Amplifiers Applications 

  • In reply to Zak Kaye:

    Zak,

    The effective resistance (or equivalent resistance) of my bridge is 109.091 ohm. And if I disconnect the bridge, I do get the expected 2.5 volt.

    I am attaching herewith the diagram

    So, what should be the net resistance of my bridge so that I can get the expected 2.5 Volts or any other reference voltage as given in the datasheet.

    Regards,

    Captain

  • In reply to CAPTAIN SWING:

    Normally, the datasheet should specify what the drive capability of the reference is, but for some reason this was not done for the INA126. I can confidently say that 100 Ohms is too low of a bridge resistance for the reference to drive (would require roughly 25mA), but it is difficult to say what the minimum resistance you need would be. If you have the flexibility to increase your bridge impedance I would suggest increasing to over 2.5kOhm so that the reference doesn't need to supply more than 1mA (this is generally a safe limit for a reference).

    Alternatively, you could add a transistor as in figure 4 in the datasheet to boost the output current.

    Regards,

    Zak Kaye
    Precision Amplifiers Applications 

  • In reply to Zak Kaye:

    Hi Zak,
    Due to some experimental constraints, it is almost impossible for me to increase the impedance of the bridge to 2.5 kilo ohms. Of course, I would consider using the transistor and come back to you.
    But for my present problem, where I need to get high voltages (between 2.5 to 10 volts) to excite the Wheatstone bridge, can you suggest any other instrumentation amplifier or operational amplifiers, where I could get these voltages with the present bridge impedance of 109.091 ohms.

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.