@@ -107,6 +107,8 @@ Evaluating these, we can create the graphs below:
These measurements are pulled from a single measurement on the sensor, so I expect averaging will reduce some of this nonlinearity. I also want to play with the sensor gains to increase the region before the internal ADC overflows. The goal of this will be to maximize dynamic range, which we could evaluate as the ratio of full scale to the standard deviation of the nonlinearity. In the simple measurements above, this dynamic range is roughly 8 bits. If we oversample 16x, we can get 10 bits at 150 Hz. If we turn down the gains, we may work further above the hall elements' noise floors, additionally increasing dynamic range. We also can turn on hall element $`C_5`$ which could increase dynamic range at no bandwidth penalty.
These measurements are also just at the edge of the positioning we can expect from our stage. In fact, we can see the limits of stage repeatability in the graph at left, where an artifact shows at the left due to overscanning the grid and the misalignment between consecutive scans. This ramifies in the nonlinearity measurement of the $`x`$ coordinate where we see large values up until the misalignment. I take all this to mean we should hurry up and get to the full system before spending too much time on testing, but we might expect ~12 bits of dynamic range at ~150 Hz with ~100nm noise floor, given optimal parameter tuning.
Below we show a new design incorporating this magnet change and rotating the ICs to give differential measurements in all axes.
