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How to use INA114

alfredo macpherson
Prodigy 30 points
Other Parts Discussed in Thread: INA114, TINA-TI

Hi, im trying to use the ina114 with a load cell
to use this I search in internet and I only find the same things, to make a wheatstone bridge with the load cells, put a 5v signal in to the bridge, when I do this i can read the output voltage with a volmeter (some few mV) it changes from 0.2mV to 0.8mV, but when i pass this signal througth the ina114, it gives me always the same voltge 4.33v.
this is the load cell that i use
http://proto-pic.co.uk/load-sensor-50kg/
this is the schematics
http://www.proto-pic.com/Resources/Application%20Example%20of%20using%20the%2050kg%20Load%20Sensor%20PPSEN-10245.pdf

  • 0
    Expert 1095 points

    Hi alfredo macpherson,

    In the PDF that you have attached, reference pin of the IC has not been used. And more over, for 0.8mV I/P and gain 10000 and Vs=5v will result in saturation of the OP-AMP. Check the TINA file that I have attached. You can get this software TINA from here http://www.ti.com/tool/tina-ti6661.qaz.TSC

  • 0 in reply to Deepak%20murali
    Prodigy 30 points

    Hi, 
    well, the thing is that de datasheet of the ina says that i can use a resist of 5ohm
    if i put a resist of 30ohm or less, it does not work, the same for a resist of more than 300 ohm it also does not work...  thanks for the answer

  • 0 in reply to alfredo macpherson
    Expert 1095 points

    Hi,

     Are taking about the following lines in the data sheet?  

    "The output is referred to the output reference (Ref) terminal which is normally grounded. This must be a low-impedance connection to assure good common-mode rejection. A resistance of 5Ohm in series with the Ref pin will cause a typical device to degrade to approximately 80dB CMR (G = 1)."

    You directly connect the reference pin to the ground(no need of any resistor). The above lines from the data sheet tell, how bad the OP-AMP start reacting, if you increase the resistance value between GROUND and reference pin of the OP-AMP. 

  • 0 in reply to Deepak%20murali
    Prodigy 30 points

    Hi Deepak!

    Thanks for the support! indeed I've follow your instructions and make the INA work. BUT it seems it might not be the amplifier I need.

    You see, I'm trying to read a voltage from 2 load cells (50 Kg) ..And it seems to work with the INA114, however it seems to saturate with small amounts.

    Can you recomend me an TI amplifier for this?

    Thanks

  • 0 in reply to alfredo macpherson
    Expert 1095 points

    Hi,

        If saturation of output is your problem, then with the same amplifier try to increase power supply. Note this point in first page of the data sheet.  WIDE SUPPLY RANGE: ±2.25 to ±18V 

  • 0 in reply to alfredo macpherson
    TI__Genius 12335 points

    Also, as was mentioned before, you can reduce the gain of the amplifier so that it does not saturate with your input voltages. The proper gain can be calculated using Vout(max) / Vin(max) = Gain, then the proper resistor value to produce this gain is selected using the equation from the datasheet. The maximum output voltage that the INA114 will be able to produce is determined by the power supply that it is operated on.