Abstract: This paper designs an intelligent strain-based online viscosity sensor based on a microcontroller and presents the external structure of the sensing element. The hardware circuit uses a low-power microcontroller AT89C55WD as the microprocessor, and continuous output of the online viscosity measurement signal is achieved through software programming. Experiments verify that the sensor can effectively acquire the viscosity signal, ensuring the real-time performance and accuracy of viscosity measurement. Keywords: Viscosity sensor, Online viscosity measurement, Microcontroller 0 Introduction Viscosity measurement has wide applications in industrial production and scientific research, such as: design of fluid transport systems, design of chemical machinery, quality control and process control of raw materials, semi-finished products, and finished products in the polymer chemical industry, scientific research of polymer compounds, pharmaceuticals, printing and dyeing, and oil extraction. With the increasing requirements for product quality control, traditional laboratory measurements or delayed inspections can no longer meet the requirements, and the application and demand for online measurement are becoming increasingly widespread. Based on the analysis of fluid characteristics, this paper designs a viscosity sensor and, through hardware circuit design and software programming, realizes the acquisition and processing of viscosity measurement signals, ensuring the real-time performance and measurement accuracy of viscosity measurement. 1 Working principle and design of viscosity sensor 1.1 Measurement principle According to fluid mechanics theory, when a medium flows in a pipe, a flow-blocking element is installed in the flow-facing direction at the center of the pipe (ensuring that the flow-blocking element and the pipe are coaxial). When the medium flows through, it will inevitably exert a force on the flow-blocking element. This force can be summarized as consisting of two parts: fluid dynamic pressure and viscous friction. When the flow rate is large, the fluid dynamic pressure plays a dominant role. It is proportional to the square of the fluid velocity, the fluid density, and the area of ​​the flow-facing surface of the flow-blocking element [1]. When the flow velocity and flow rate decrease, the kinetic energy of the fluid decreases accordingly, and the dynamic pressure of the fluid on the flow-blocking element also decreases accordingly. At this time, the force on the flow-blocking element mainly comes from the viscous friction between the fluid and the flow-blocking element, that is, viscous friction (including inner wall friction and outer wall friction). As long as the fluid continues to flow, the flow velocity cannot be zero. Therefore, the inertial impact force of the fluid on the flow-blocking element cannot be reduced to zero. However, by designing the flow-blocking element, the dynamic pressure can be reduced and the viscous friction can be increased. This results in increasing the contact area between the fluid and the flow-blocking element, and reducing the upstream area that causes the dynamic pressure. Based on the above analysis, a tubular viscosity sensor was designed, as shown in Figure 1. Due to the thinner tube wall, the inertial impact of the fluid on the flow-blocking element is reduced. For tubular flow-blocking components, viscous friction is generated on both the inner and outer walls as the fluid passes through. Mechanical theory analysis shows that the viscous friction force on the tube reaches its maximum value when the friction force on the inner wall is equal to that on the outer wall. For details, please click: Design of Intelligent Strain Online Viscosity Sensor