The reaction amount of the reagent and sample of the automatic biochemical analyzer is slightly upgraded

and the accuracy of the sample is not enough to make the test result deviate. In response to this situation

a design of liquid level detection system is proposed. The system regard sampling needle as capacitive sensor of liquid level

and the capacitive sensor uses a dedicated integrated differential detection chip CAV444 to output the capacitance change signal as a differential voltage signal. The STC12 C5410 AD chip is used to analyze the sensor A/D data to achieve accurate judgment of the liquid level. The test results show that the system has high measurement accuracy

small error and stable performance. The average contamination rate of the test sample is0. 012 %. The accuracy and repeatability of the sample meet the relevant requirements of the industry standard.