You need to adjust the offset. As you can calculate, your bridge offset voltage is
Vos = Vout/gain = 18.8mV/5 = 8.81/2358 ≈ 3.7mV. You need to add an offset adjustment circuit, as in Fig. 2 in the datasheet (see attachment). This will compensate for the offset at any gain setting. The highest gain should give the best settability.
BTW, how did you get gain=2358 for Rg=80? The equation is
Gain=5+200k/Rg.
When Rg=80, Gain=2505. Did you mean Rg=85?
EDIT: Keep in mind that no rail-to-rail op amp will go all the way to either rail. I would set the gain high, adjust the offset down until it won't go any lower, then turn it up (or down, as required) until the output barely starts to move.
Note that, if your offset happened to be the opposite polarity, prior to adjustment you would get near zero output with low or high gain, and the output would only start to move when the strain caused the differential input to be greater than 0.
Vos = Vout/gain = 18.8mV/5 = 8.81/2358 ≈ 3.7mV. You need to add an offset adjustment circuit, as in Fig. 2 in the datasheet (see attachment). This will compensate for the offset at any gain setting. The highest gain should give the best settability.
BTW, how did you get gain=2358 for Rg=80? The equation is
Gain=5+200k/Rg.
When Rg=80, Gain=2505. Did you mean Rg=85?
EDIT: Keep in mind that no rail-to-rail op amp will go all the way to either rail. I would set the gain high, adjust the offset down until it won't go any lower, then turn it up (or down, as required) until the output barely starts to move.
Note that, if your offset happened to be the opposite polarity, prior to adjustment you would get near zero output with low or high gain, and the output would only start to move when the strain caused the differential input to be greater than 0.
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