Department of Computer, Changzhi University, Changzhi, Shanxi, China.
School of Medical Information Engineering, Guangzhou Univ Chinese Med, Guangzhou, Guangdong, China.
PLoS One. 2024 Apr 18;19(4):e0298282. doi: 10.1371/journal.pone.0298282. eCollection 2024.
Liquid level detection system is an essential core functional component of automatic clinical medical testing instrument. The conventional liquid level detection method has low detection accuracy and sensitivity, and may have the problem of false detection, which may lead to the inaccurate test results. This paper presents a high sensitivity liquid level detection system based on the principle of variable capacitance. When the sampling probe contacts the liquid level, the probe capacitance will change. The liquid level detection circuit board judges whether the probe contacts the liquid level by sensing the change of probe capacitance. When judging the liquid level signal, the combination of slope detection and amplitude detection is used. The liquid level detection circuit board takes the phase-locked loop(PLL) circuit as the center to detect the change of the capacitance. The reference signal of the PLL is set as a square wave of 375kHz. The double tube probe is used as a part of the tuning capacitor of the voltage controlled oscillator to control the frequency of the output signal, which can realize the rapid phase locking. The experimental results show that the system has accurate detection results, high sensitivity, stable and reliable operation, good dynamic response performance in the case of large and small liquid volume. Compared with other liquid level detection methods based on machine vision, ultrasonic, optics and so on, the proposed liquid level detection system has simpler structure and lower cost, it can avoid the problems of collision, carryover contamination and empty suction by controlling the depth of sampling needle inserted into liquid.
液位检测系统是自动临床医疗检测仪器的核心功能组件之一。传统的液位检测方法存在检测精度和灵敏度低的问题，并且可能存在误检的问题，这可能导致测试结果不准确。本文提出了一种基于变容原理的高灵敏度液位检测系统。当采样探头接触到液位时，探头电容会发生变化。液位检测电路板通过感测探头电容的变化来判断探头是否接触到液位。在判断液位信号时，采用斜率检测和幅度检测相结合的方法。液位检测电路板以锁相环（PLL）电路为中心，检测电容的变化。PLL 的参考信号设置为 375kHz 的方波。双管探头用作压控振荡器调谐电容的一部分，以控制输出信号的频率，从而实现快速相位锁定。实验结果表明，该系统具有准确的检测结果、高灵敏度、稳定可靠的运行性能，在大、小液体体积的情况下具有良好的动态响应性能。与基于机器视觉、超声、光学等其他液位检测方法相比，所提出的液位检测系统具有更简单的结构和更低的成本，它可以通过控制采样针插入液体的深度来避免碰撞、残留污染和空吸等问题。
