A noniterative polynomial 2-D calibration method implemented in a microcontroller

Output signal handling of a smart sensor usually involves a calibration facility to correct for input-output nonidealities which comprise offset, gain errors, nonlinearity errors, and cross sensitivity. In this paper, a calibration method is presented which features a progressive improvement in the sensor calibrated transfer toward the desired transfer as the user proceeds from one calibration point to the next. The method is based on a set of mathematical formulas whereby a calibration coefficient is calculated at a selected calibration point and used to calculate a first correction of the sensor transfer curve. Further improvement in the sensor transfer is obtained by repeating the process for a second calibration point using the transfer resulting from the first calibration, without the need to review the calibration already carried out at the first point. The process can be repeated until the desired error reduction is obtained. Step by step, the calibration method builds up a polynomial transfer correction. Simulation results are shown to demonstrate the performance of the method, A software implementation of the method for two-dimensional (2-D) calibration in an 8-bit microcontroller is presented. The microcontroller with calibration program can be incorporated in a compact smart sensor system