基于采样保持原理的高精度电导率检测电路

High Precision Conductivity Detection Circuit Based on Sampling and Holding Principle

文中设计了一种基于采样保持原理的高精度量程自适应电导率检测电路,以双极性交流方波作为激励信号源,通过采样保持的方法对电导池两端的交流电压及流经电导池的交流电流信号差分化并进行采集,同时使用铂电阻作为温度传感器对测量得到的电导率进行温度补偿。双极性交流方波激励信号有效降低了交流正弦信号作为激励源时电极电容效应和极化效应所引起的误差,差分式采样保持电路减少了外界环境变化引起的电路噪声,量程自适应电路保证了电导率测量的宽量程,通过上述方法弥补了传统电导率测量电路定量程、测量范围窄、精度低的缺点。测试结果表明:文中设计的电导率测量电路测量范围为0.1~40 000μS/cm,重复性误差小于1%,测量基线噪声小于0.25 nS/cm。

In this paper,a high-precision range adaptive conductivity detection circuit based on sampling and holding was designed.Bipolar AC square wave used as the excitation signal source,and the differential of AC voltage at both ends of the conductancecell and the AC current signal flowing through the conductance cell were collected by sampling and holding method.At the same time,platinum resistance was used as the temperature sensor for temperature compensation of the measured conduc-tivity.Bipolar AC square wave excitation signal effectively reduced the error caused by electrode capacitance effect and polariza-tion effect when AC sinusoidal signal was the excitation source,the differential sampling and holding circuit reduced the circuit noise caused by the change of external environment,and the range adaptive circuit ensured the wide range of conductivity measu-rement.The above method made up for the shortcomings of the traditional conductivity measuring circuit such as fixed range,nar-row measuring range and low accuracy.The test results show that the conductivity measuring circuit designed in this paper has a measuring range of 0.1~40000μS/cm,repeatability error is less than 1%,and baseline noise is less than 0.25 nS/cm.