Development Of A High Precision Instrument For Raw Milk Freezing Point Measurement

Raw milk is unprocessed normal milk that is immediately taken out from healthy milk cow. To ensure service safety of raw milk and dairy products, the quality of raw milk must be monitored. Freezing point of raw milk is one of the important indexes indicating the quality of raw milk. Detection of the freezing point of raw milk based on Raoult's law (Freezing-point Depression: FPD) is a common method used to examine the quality of raw milk. In theory, this method has many advantages, such as high measuring accuracy, good stability, etc..Aiming at developing a high performance freezing point measuring instrument, based upon the national standard titiled'Determination of freezing point in raw milk (GB5413.38-2010)', the mechanical structure and the electronic circuit of the instrument was designed with MSC1210 as the micro-processor, a high accuracy and negative temperature coefficient (NTC) thermistor as the temperature measuring probe, and the instrument software package was programmed.The main content of the thesis includes the following aspects:1. Based on the investigation of milk freezing point measuring instrument, the present situation of milk freezing point measuring instrument domestically and abroad, was reviewed. According to Raoult's law, a general design scheme was proposed.2. The overall mechanical structure using 3D graphics software was designed and optimized, including: two positioning mechanism, Amplitude Modulated (AM) stirring mechanism, circulating refrigerating mechanism.3. The electronic circuit was designed, including: high precision temperature acquisition circuit, semiconductor refrigeration circuit, clock circuit, monitoring circuit of environmental temperature and humidity, touch screen and printer circuit, communication circuit, data storage circuit, etc..4. Instrument software package was programmed, including: the host computer sub-program, measurement sub-program, calibration sub-program, AD conversion sub-program, printer sub-program, touch screen sub-program, encrypt and dormancy sub-programs.5. Experiments were conducted to verify the main functions of diffrient modules and overall performance of the instrument. 6. The instrument performance was summized, and the existing problems were brieftly introduced with ways of resolutions proposed.