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Instrument Amplifier For Gas Analyzer Assistance Needed

Question asked by KyAZ on Nov 27, 2013
Latest reply on Dec 21, 2013 by KurtBecker

Hello.  I am requesting some assistance on a circuit I am wanting to design.  This design is a gas analyzer with a local lcd display.  I have a Figaro KE-25 oxygen sensor, that has a 0% to 100% oxygen level range.  This oxygen level is represented by a mV signal comming out of the sensor.  The problem i have with this sensor is that when oxygen concentrations are low, there is a voltage offset due to the sensors characteristics (http://www.figarosensor.com/products/offset.pdf). When I put span gas (25% oxygen) to the sensor my existing circuit displays the value correctly.  When i put zero gas (0% oxygen) to the sensor my existing circuit displays 2%~3% oxygen.  First, i need to find an instrument amplifier ic that has very small offset voltage and input bias current (<10nA).  Second, I need this amplifier to accomodate adjustable external zero and span components, which i am assuming is gain and offset.  Once the amplifier's gain is set to whatever i choose, i need to be able to adjust the output at low levels of oxygen (0%) for correct display of oxygen percentage.  If anyone can help me with the amplifier selection and the zero and span portion of the circuit, i would be entirely grateful.

 

Thank you,

 

Kyle

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