# Accelerometer question

Hi, I;m en engineering student working on a project for my measurements class, whenever you have a 3 AXIS accelerometer anmd the uncertainty is given as +/- 1.5/ 4/ 6/ ect. like in this item pololu.com/catalog/product/766

what are the units for g? are they G’s like in G- force? in newtons? grams?

Hello.

The ±1.5/6g is not an uncertainty, it’s the sensitivity/range of the part. When the accelerometer is configured to ±6g, it can measure accelerations ranging from -6g to +6g, and it is less sensitive than when it is configured to ±1.5g, which measures accelerations over a smaller range (-1.5g to 1.5g) but with a higher resolution.

If you look at the datasheet for the part, you can find the zero-g voltage output along with the sensitivity, in terms of volts per g, which means you can convert the voltage output to an acceleration in units of g as:

accel = (Vout - Vzerog) / sensitivity

The units are given in terms of the acceleration of gravity near the surface of the Earth (g). You can easily express g in other units if you want (e.g. 9.80665 m/s^2, 32.174 ft/s^2, ??? parsecs / lunar month / ms).

Using units of g is like using astronomical units (AU) to measure distance or solar masses to measure mass. What are the units for a star’s mass expressed in solar masses? Well, by definition, the units are “solar masses”, but you can still convert it to more familiar/standard units by substituting “solar mass” with the mass of the sun in, say, kilograms.

- Ben