Research On The Measurement Systems Of Nondestructive Vacuum Degree Based On Dual Eddy Current Sensors

Vacuum degree of the can food is one of the most important quality characteristics. Up to now, there are a lot of methods for the vacuum degree measurement, such as photoelectric method, inductive method, electrical pulse method, eddy current method, ultrasonic method, vacuum meter method and manual method. In these methods, the electrical pulse method and the ultrasonic method are the most widely used methods in the foreign food factories. For the measurement instruments with these two methods are very expensive and have special requirements for the operational environment, these instruments are only used in a few advanced production lines. And the manual method is still the main method in the factories of our country. For the characteristics of low accuracy and deconstruction of the manual method, it can't be used in automated detection in production lines.Based on a deeply analysis on the theories and researching results, according to the requirements of the factories, a vacuum degree nondestructive measurement instrument is studied and it is certified with a lot of cases. The main contents of this thesis are listed as below.1. The theory of the eddy current measurement method is studied and the system structure and the circuit of the measurement instrument are designed.2. The measurement method of the dual eddy current sensor is studied. With a large number of experiments, the relationship among the output voltage of the sensor, the tiny distortion and the vacuum degree is analyzed. Furthermore the curve and function between the output voltage and the vacuum degree are found too.3. In practice, for the difference of the height between the can, the accuracy of the instrument is affected. Thus the relationship between the height of the can and the measurement accuracy is studied with the simulation method. And the function between the height of the can and the accuracy is found. Furthermore, an error compensation method is designed and the accuracy of the instrument can be improved obviously.4. The vacuum degree measurement instrument with the data processor of a single chip microcomputer, 89C58, is developed. An adaptive correction method for reducing the influence of all kinds of factors, such as temperature, material of the can and atmospheric pressure etc, is introduced. And the reliability of the instrument is improved obviously. Thus this kind of instruments can be used both in the environment of dynamic on-line measurement and in laboratories. It is certified that the error rate of this instrument is less than 5%.There are some perfect characteristics of the instrument developed in this thesis, such as high accuracy, low price and high measurement speed. And the successful development of this instrument is helpful for the resolving the problems in the vacuum degree measurement in our country.