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INA125P interface with ADC of Microcontroller

NIKHIL VALIYA VALAPPIL
Intellectual 520 points
Other Parts Discussed in Thread: INA125

Dear SIr / Madam,

I am trying to interface a loadcell with controller's PLC which can read 0 - 10V or 4- 20mA of analog signal.

I tried to interface loadcell with PLC but got failed. After some searching on web i became to know that INA125P helps to interface loadcel with other devices. So i order sample of INA125P to try.Unfortunately the same result repeats here also.

I used the connection same described in starting of datasheet of INA125P. Used Rg =10k and sleep tied up with VCC.

Used power of 5v which is regulated from 7805.

Loadcell details:

 Red - V+ : 5VDC

Black - Gnd : Gnd

Green - Signal +

White - Signal -

Operating Volt : 5vdc

Maximum Load :3kg.

when i checked the signal output using multimeter its showing +2.5v for both signal of loadcell without any load on loadcell and not connected to INA125P. but while connected to INA 125P its showing some mv on meter and it varies each poweron time. but not varying output while applying load on load cell.

why it is like this?

Does i did any mistakes in wiring ?

I am trying to get voltage varying output to interface with PLC analog module. Please help to  overcome this issue.

Enclose herewith the schematic diagram of INA125P. Find the diagram for more details.

Regards,

Nikhil V V

  • 0
    TI__Genius 12325 points

    Nikhil,

    Just to clarify what you wrote, both outputs of the load cell are pull down to a couple of mV when the INA125 is connected or the output of the INA125 is only a couple of mV?

    I should point out that with a 5V supply, the reference output voltage cannot reach 5V due to the required dropout voltage of 1V:

    The INA125 would have to have a supply voltage greater than 6V to properly output 5V from the reference. Also, the output of the INA125 can only swing about 400mV from its negative supply voltage (0V in your case):

    This will limit the accuracy of your system for light loads. 

    If the INA125 is actually pulling down the output of the load cell to ground, the INA125 may have been damaged and you should try replacing it with a new part. Proper ESD precautions need to be taken when handling integrated circuits. The parts should be stored in an ESD safe bag and the person assembling the board should be wearing an ESD wrist strap or other grounding device and working on a static dissipative surface. 

  • 0 in reply to John Caldwell
    Intellectual 520 points

    Dear Sir,

    Thank you for your support.

    Sorry for the late reply.

    Recently  again i checked Loadcell  by giving 5vdc to loadcell from regulated supply.

    And i checked the out put of loadcell using multimeter i got it varying in few mV range of 0 to 10mV while applying load. Here INA152P not used for testing.

    Next step is amplifying the output from mv to voltage level by using INA125P with gain resistor of 680 ohm.

    Calculated gain and Output voltage is,

    G = 4+64K / Rg

    G = 92.24

    min output of INA125P = 0V

    max output of INA125P = 922.3 mV


    The circuit connection which i am going to use for testing as follows.

    Please make a correction if i did any mistake. Or should i notice any other things rather than these points?

    Hope the points are clear.

    Thanks and regards,

    Nikhil