基于弧形电容器的浆纱回潮率在线测量

Online measurement of moisture regains of sized yarns based on arc capacitance sensor

为提高上浆质量以及解决使用接触式电阻含水率测量仪会破坏浆膜的问题,设计开发了基于弧形电容器的浆纱回潮率在线测量系统。根据浆纱在弧形电容器中的电场模型和电容法测量原理,利用指数回归算法建立电容差与回潮率的函数模型。上浆时,浆纱穿过弧形电容器,电感、电容、电阻(LCR)电桥测试仪将测量的电容值数据传到上位机,上位机根据模型计算出实时浆纱回潮率。讨论了弧形电容器结构、LCR电桥测试仪测试参数、环境温湿度、浆液含固率、浆纱线密度、回潮率对测量电容值的影响。实验结果表明:电容值受LCR电桥测试仪测试频率的影响较大;电容值随电容器结构参数极板长度、极板包角的增大而增大,与极板曲率半径呈负相关;环境温湿度会对电容值产生复杂影响,因此要求在恒温恒湿条件下进行测量;浆纱回潮率对电容值的影响显著,且回潮率与电容差呈指数函数关系。在上浆机上使用电容式回潮率在线检测系统进行测试,得到的浆纱回潮率与烘箱法测量结果相比平均误差小于5%,本文系统具有一定的工程实用价值。

Objective In order to fulfill the online detection of the moisture regain of the sized yarn in the sizing process,to improve the sizing quality,to reduce the carbon emission caused by sizing,and to solve the problem that the use of a contact type resistive measuring instrument may damage the sizing film,a measurement system for sizing moisture regain was developed.Method According to the electric field model in the arc capacitor and the measurement principle of capacitive method,the model relating the capacitance difference and moisture regain was established.The sized yarn passed through the arc capacitor,and the LCR(inductance,capacitance,resistance)bridge tester captured the capacitance signal and transmitted it to the computer.The moisture regain of the sized yarn was calculated according to the model.The influences of the structure of the arc capacitor,the test parameters of the LCR bridge tester,the test environment,and the solid content of the slurry on the capacitance readings were discussed.Results The experimental results show that the parameters of voltage,acquisition frequency,and internal resistance of the LCR bridge tester have little effect on capacitance value,while it is greatly affected by the testing frequency(Fig.3).At the frequency of 4000 Hz,the capacitor was found to have the most significant response to water content(Fig.4),and hence 4000 Hz was selected as the testing frequency of LCR bridge tester.It was revealed that as the curvature radius of the arc capacitor’s electrode plates increases,the capacitance value decreases,and that when the length of the electrode plate increases,the capacitance value increases.With the wrap angle of the electrode plate was increased,the capacitance value also increased(Fig.5).The capacitance simulated by the finite element technology were consistent with the measured results.The differences between the measured and the simulated values are caused by additional capacitance and environmental interference.Temperature and humidity were found to have a complex impact on the capacitance value(Fig.6),indicating that the system should be deployed under constant temperature and humidity conditions.The moisture regain of sized yarn demonstrated a significant effect on the capacitance,while the influence of fineness and size solid content were not obvious(Fig.7),where it can be seen that moisture regain is nonlinearly related to the capacitance difference.When moisture regain was increased,condensed water on and inside the yarn increased and a strong polarization reaction occurred at the frequency of 4000 Hz with the capacitance value increasing.An exponential regression model of capacitance difference-sizing moisture regain is established.On the sizing machine,the capacitive sizing moisture regain online detection system developed by the research was adopted to measure the sizing moisture regain.Compared with the results of the oven method,the average error sizing moisture regain measurement was less than 5%(Tab.1).Conclusion The capacitance value is greatly affected by the test frequency of the LCR bridge tester.The structure of the arc capacitor also influences the test capacitance value.The ambient temperature and humidity have complex effects on capacitance values.The influences of sized yarn moisture regain on capacitance are significant,while fineness and size solid content are not so obvious.The core components of a capacitive sizing moisture regain measurement system designed include an arc-capacitor sensor,an LCR bridge tester and a computer.The arc capacitor has a small and simple structure with low cost.It can measure sized yarns in a non-contact manner.Therefore,this system can be used in engineering practical situations.