Study On Detection Method Of Water-holding Capacity Of Beef Based On Liquid Level Sensor

Water-holding capacity is one of the most important indexes of beef quality, and it decides beef products'quality indexes such as texture, tenderness, taste and the economic indexs such as yield rate, it also decides mass loss during beef production process and quality of the product. In order to produce high quality beef products, problems of output and mass loss caused by low water-holding capacity become the attentive focus, detection of beef water-holding capacity is of great significance in beef production process.In this thesis, water-holding capacity of flesh beef is researched. On the basis of existing water-holding capacity detection method, relevant factors of water-holding capacity are analyzed and detection method using liquid level sensor is proposed. Beef water-holding capacity detection system including mechanical extrusion device, liquid level sensor, data acquisition and treatment system and control system is developed, experiment is carried out in order to verify the detection system's effectiveness.1. The relationship between liquid level and water-holding capacity is analyzed and mathematical model of liquid level sensor is established based on the principle of liquid level change leads to capacitance signal change. The theoretical sensitivity of the liquid level sensor model is 0.1271pF/mm according to the analysis of mathematical model. According to theoretical analysis and experiment requirements, a non-contacting capacitive liquid level sensor is designed, experiment of electrode width's impact on sensitivity of the sensor is executed. The best electrode width is determined.2. In order to measure the liquid level change exactly, AC excited C/V conversion and amplification circuit is used as the core circuit, and related hardware circuit of data acquisition system and control system is designed. Problem of capacitance signal measurement which can be affected by empty tube capacitance, stray capacitance, and coupling capacitance is solved by using precompensation method and phase sensitive demodulation. According to theoretical analysis, simulation under Multisim9 environment and considering every chip's normal working conditions, major parameters of the capacitance detection circuit, reference signal of phase sensitive demodulation, and capacitance of precompensation are confirmed. Relevant experiments are carried out and the results show that measuring accuracy of capacitance is highly improved by such real time compensation method of combining software and hardware.3. STC89C52RC MCU is taken as the core control chip of the detection circle, and the MCU software is developed under Keil C51 software integration development environment. According to the role of the MCU in the detection system, the MCU main program, T0 interrupt service routine and data treatment module are programmed. T0 interrupt service routine is the major part of the whole detection system, it includes sum of empty tube capacitance, stray capacitance and coupling capacitance detection subroutine, the variable quantity of capacitance detection subroutine, the stability detection subroutine and the communication subroutine.4. Software of Beef water-holding capacity detection system based on liquid level sensor is developed under Visual C++6.0 environment, the software is made up of the following modules: human-computer interface module, serial port communication module, data acquisition module, data processing module. The serial port communication, control of the detection circuit and data acquisition and processing are implemented by operating the human-computer interface.5. Characteristics experiments of liquid level sensor and hardware circuit are carried out using the designed water-holding capacity detection system, the experiment results show that: sensitivity of the detection system is 211.54mV/pF, nonlinear error is 0.986%, static measurement error is 0.939%, capacitance value is nearly unchanged during 10 minutes'detection, the detection system is of high detection ability.6. According to the detection ability of the detection system, mechanical extrusion device is designed and manufactured. In order to achieve the same water-holding capacity value as the value measured by pressure water loss rate method according to the agricultural industry criteria NY/T 1333-2007, uniform optimization design is adopted to optimize the force condition of the beef sample. The error between the experiment result and the value detected in NY/T 1333-2007 is only 0.346%.7. Experiment is carried out on the basis of the relationship between liquid level and capacitance value, relationship between liquid level and water-holding value, the curve between liquid level and capacitance value is obtained, the functional correlation coefficient is R2=0.9964 under quadratic polynomial regression; the curve between liquid level and water-holding value is obtained, the functional correlation coefficient is R2=0.9953 under quadratic polynomial regression. Capacitance value, liquid level and water-holding capacity is highly related.8. According to detection range of the liquid level sensor, the minimum water-holding value which the designed system can detect is 77.369%, the detection range can satisfy the detection requirement of flesh beef. Accuracy and precision of the detection system is analyzed, the relative error between water-holding capacity value detected by the detection system developed in this thesis and value detected in NY/T 1333-2007 using pressure water loss rate method is 2.1557%, coefficient of variation is less than 5%, the accuracy and repeatability satisfy the requirement.