Testing OpAmp with Pressure Sensor (Part 1)

After arranging all the bits of pressure sensor and dual source OpAmp configuration on the breadboard, I ran a few preliminary weight measurement tests to get some idea of the range of measurement possible with different levels of amplification (i.e. varying the input voltage and gain).

The above chart shows the output voltage for a given weight plotted for the various levels of amplification with the low end registering just about 0.5V for 35lbs while on the high end, the signal was closer to 5V for the same weight.

Note that the weight is also plotted on the secondary y-axis as reference and, taken together with the voltage trends, appears to indicate that the higher output voltage had a higher degree of direct correlation to the weight/pressure while the lower output voltage lagged a bit.

In any event, the two variables (output voltage, weight/pressure) were clearly very strongly correlated regardless of level of amplification indicating (to me at least) that reliable measurements will likely be able to be rendered with even limited amplification.

The key now is in determining:

1. The weight/pressure range required for the application.
2. The influence of the amplification on the stability and repeatability of the measurements.
3. The minimum level of amplification ( ... and input voltage) required to reliably attain accurate measurements within that range.
4. The minimum configuration (i.e. single versus dual source OpAmp, better OpAmp for lower power sources) needed to deliver said accurate measurements.

Below is a list of scatter-plots showing the (obviously) strong correlation between the weight applied to the sensor and the output voltage using LOW, MID-LOW, MID and HIGH amplification settings.

Notice that while all correlations are stronger than an r-squared of 0.90, the higher amplifications yielded near r-squared at or above 0.99.