Title: Automatic Calibration of a Capactive Level Detector

Speaker: Mattias Moren

Time and Place:

Wednesday, January 30th, at 15:30
Library, floor 2 at Magistern, Dag Hammarskjölds väg 31, Uppsala

Abstract:

A level detection function implemented in a pipetting system has been studied. The pipetting system is used for liquid aspiration on the Pharmacia UniCAP system. The level detection is based on capacitive measurement with the purpose of detecting pipette contact with a liquid surface.

The detection signal is dependent on a number of variables. To increase the robustness of the level detector it should be automatically calibrated for these variables. By creating and evaluating theoretical models of the level detection system the factors affecting the detection signal have been identified. Laboratrory tests on instrument prototypes were used to verify the theoretical results and to measure the effect of each variable.

A number of methods and algorithms for automatic calibration of the level detector have been developed to compensate for each of the factors identified. Methods for both continous use during operation and one-time use during production have been considered. The recommended solution has the following features:

• One-time calibration for hardware dependence during production.
• Continous calibration of detection thresholds during operation to compensate for time dependent factors, e.g. liquid volumes.
• A retrial function to double-check that the pipette really is in contact with the liquid.