|| Master Thesis Seminar at the Signals & Systems Group
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
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
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.