Circuit Design Of Intelligent Electronic Analytical Balance With 210g/0.1mg

Electronic analytical balance is the high-accuracy instrument for mass measurement, which is widely used in national defense, scientific research, factories, and laboratory quality standards for mass measurement, with high accuracy and fast response, good stability and so on. In order to guarantee the merit mentioned above, the consideration of real-time, accuracy, stability and reliability are required and the circuit performance becomes critical to the measure performance of electronic analytical balance.In this thesis, for a type of intelligent electronic analytical balance, a cooperative project supported by Hunan University and Shanghai Precision & Scientific Instruments Co., the circuit of electronic analytical balance is designed with low noise, high accuracy, high stability, in which based on high performance passive components, low noise operational amplifier, high accuracy△-∑A/D converters and voltage reference, high precision temperature sensor, ultra-low power microcontroller and so on.Firstly, the situation of the development of electronic analytical balance is analyzed and compared at home and abroad. Furthermore, the current state of the electromagnetic force balance sensor and electronic circuit is described, which are a crucial part of the electronic analytical balance, as well as the significance of the research and the focus of this thesis are pointed out. Meanwhile, the working principle of electronic analytical balance is introduced; the design of electronic analytical balance system and function are given.Secondly, a complete circuit design of electronic analytical balance is constructed. In the design of analog circuit, a photoelectric detection circuit is used to achieve the transformation from the tested samples mass to electric signal, a current signal with enough drive capability through PID regulator and power circuit is outputted, which flows to the electromagnetic force balance sensor coil and high-precision, low drift sample resistors. Then the anti-aliasing low-pass filter circuit is exploited to the extraction of useful signal and noise filtering of the voltage signal of the sample resistance. In the design of digital circuit, the voltage signal and temperature signal is detected and transformed accurately from analog signals to digital signals by using data acquisition circuit. In addition, temperature measurement circuit and peripheral configuration circuit, the communication interface, clock, wind door detection, man-machine interface modules of the SCM management system are designed to provide hardware conditions for achieving all the functions of electronic analytical balance.Thirdly, the anti-jamming design of electronic analytical balance circuit is investigated. For instance, the devices noise, radiation noise and conduction noise which impacted the circuit are analyzed. The impact of devices noise is reduced by optimizing the choice of components, conduction noise generated by the external electromagnetic radiated noise and circuit noise is reduced by various measures to attain a low-noise circuit design of electronic analytical balance, such as the grounding methods, power supply interference rejection, printed circuit board design and so on.Finally, according to verification regulation for electronic balance, the electronic analytical balance is completed the experiment test to examine the partial load error, repeatability error and indication error by using the F1 grade standard weight. Additionally, the test results of electronic analytical balance are analyzed, and the error factors of electronic analytical balance are discussed.The above-mentioned design of electronic analytical balance meets the design requirements with scale range of 210g, accuracy of 0.1 mg, and it is of high accuracy, good stability, and fast response.