Triaxial Accelerometer Options

The dynamic range refers to the ratio of the largest to the smallest signal recordable, expressed in dB (decibels). Each 20 dB is a factor of 10 and each 10 dB is a factor of 3. So if an accelerometer has a range of 4g and a dynamic range (DR) of 70 dB, the noise floor is 4g/3000 = 1.3 mg. This means that signals below 1.3 mg will be below the noise floor and not visible. The cost of an accelerometer increases with its DR, so it is not economical to specify an accelerometer with a greater dynamic range than the smallest signal of interest. Calculated the other way, if the smallest signal of interest is 4 mg and the range needed is 4g, the DR is 20log(4.0/0.004) = 60dB. It is prudent to add to this number about 10 dB of "headroom", so a 70 dB accelerometer would suffice. The Accel-70 and the Accel-90 are MEMS (Micro Electro Mechanical Structure) devices. The Accel-120 is a force-feedback accelerometer (FBA) using magnetics to sense acceleration. MEMS devices are manufactured like integrated circuits so are less costly but lack the FBA's performance.