Procedure for in-use calibration of triaxial accelerometers in medical applications

In the medical field triaxial accelerometers are used for the monitoring of movements. Unfortunately, the long-term use of accelerometers is limited by drift of the sensitivities and the offsets. Therefore, a calibration procedure is designed which allows in-use calibration of a triaxial accelerometer. This procedure uses the fact that the modulus of the acceleration vector measured with a triaxial accelerometer equals 1 g under quasi-static conditions. The calibration procedure requires no explicit knowledge of the actual orientation of the triaxial accelerometer with respect to gravity and requires only quasi-static random movements. The procedure can be performed within several minutes. Considering practical applications, it is found possible to obtain an average error smaller than 3% (of 1 [g]) with the calibration procedure for inputs caused by 'standing straight and moving slightly' when the offsets only are estimated. For the input caused by the sequence that occurs when going to bed, it is found possible to obtain errors smaller than 3% for estimating all parameters.