I'm looking for an single or two-axis tilt sensor that will produce voltage(s) proportional to deviation from gravitational vertical. Size, operating voltage not important. Should have reasonable accuracy ±10 degrees. It will never tilt more than that (unless it tips over )
Forget about the sinusoidal relationship of gravity with incliniation...below 20 degrees deviation from zero, the sine function is linear, so is the cosine function except centered around 90 degrees.
Those electrolytic sensors would be a more straightforward solution, but last time I checked, Spectron quoted me at $260 for a single module (that's a dual-axis sensor mounted on a PCB module with all the temperature compensation and excitation and signal conditioning). They are much larger and more delicate than an accelerometer, but more tolerant to continuous accelerations and very very accurate from -90 to 90 degrees.