Liquid Viscosity Measuring System Based On Quartz Crystal Sensor In Impedance Method

The viscosity is one of liquid important physical properties,and is very important parameter to reflect flow characteristic of liquid. Measurement of viscosity is widely used in industrial fields, such as petroleum, chemical engineering and pharmacy, and plays important role in quality control of production, as well as in the evaluation of products. Measurement of liquid viscosity is also widely used in the fields of medicine and national defence. So it has great economic and social benefit to have viscosity measured in time and precisely. With the industry developing, measurement of viscosity is developing towards high accuracy, automation and real-time. But the traditional viscosity meters, such as tubule viscometer and rotational viscometer, have a lot of shortcomings: the viscometers are too heavy to be taken, or the response time is too long for real-time measurement.According to the effect that the equivalent impedance of quartz crystal sensor increases when it is put in liquid, we designed a quartz crystal liquid viscosity measuring system using impedance method. In this measuring system, the quartz crystal is drived by constant-frequency source. And in this way the shortcomings of traditional quartz sensor, such as difficulty in starting resonating and low measuring range of liquid viscosity, are solved. This quartz crystal sensor is drived by its resonance frequency and the response signal is got from the sampling resistor. The information of liquid viscosity is got according to the correlation between the signal amplitude and the liquid viscosity.In this paper, we studied two liquid viscosity measuring methods by dipping quartz crystal into liquid, phase-shift method and impedance method. Using impedance method, we designed a new quartz crystal liquid viscosity sensor drived with constant frequency. And we designed a complete liquid viscosity measuring system based on the good correlation between the signal amplitude and the liquid viscosity. In this measuring system, we designed and completed the following tasks:①a Clapp oscillating circuit working as a frequency source to put out changeable frequency to drive the quartz crystal;②Signal processing part including mixer, low-pass filter, multiplexer and A/D change;③MCU hardware and software system including key control and LCD monitor and the MCU is responsible for data processing and monitoring control;④fitting standard curve to be the measuring system's working curve using data of experiments in liquids with different viscosities.Using our designed measuring system, we did some experiments in liquids with different viscosities and analysed the measuring error. The results showed that when our system was used in measuring liquid viscosity in the low and middle viscosity range liquid, accuracy of this measuring system can basically met the designing requirement and the measuring error was acceptable. So our system brings a new simple-structure method which can offer real-time measurement to liquid viscosity measurement in low and middle viscosity range.