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Designing an Single Supply Amplifier for a 350Ω Load Cell

The particular load cell that I was interfacing was a 350Ω resistive bridge.  The max excitation is 15v although we are going to use 5V.  The output is 3mV/V, which means the full scale output will be 15mV.  This is why we need we need the amplifier.  The output will need to be amplified by 100 to provide adequate measurement.  The load cell is “S” frame so it can be tension or compression although I will be using only in compression.  Since we are only using compression I will not have to bias up the output.  There are a couple options if we wanted to read tension and compression:

1.     We can use two power supplies and use a bipolar A/D measurement.

2.     We can use two power supplies and use a unipolar A/D measurement after we biased up the voltage to 2.5V

3.     We can use a single supply and bias up the voltage to 2.5V.

Really there is a ton of ways to read or manipulate the voltages for reading and that is not the purpose of this article.  This article will address a single 5V supply with a 16bit A/D. Our transducer will be 0-1000psi with a full scale of 1.5v, at a gain of 100, at 16bits will give me 19 data point per psi, which should be plenty.

I went with all Analog devices parts so I could simulate it all in their simulation software call MultiSim.  I used the 5V reference REF195 and their op amp OP213 which is a dual op am on an 8-SOIC.  Here is the Schematics/Simulation for MultiSim 

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