Articles
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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