The Research And Design Of Capacitive Level Meter Signal Conversion Circuit

Depending on its low price, simple structure, good dynamic response, sturdymaterial and characteristics of stable working in extreme environments such as hightemperature, cryogenic, radiation and strong vibration, capacitive level sensor widelyused in level measurement of modern oil industry, chemical industry, food industry,pharmaceutical industry and other industrial production field.But capacitive level metercommonly has the disadvantage of capacitive sensor’s high output impedance, poor loadcapacity, difficult signal processing, and this is mainly due to by dozens of pF to severalhundreds of pF of the electrical capacity of the capacitive sensor, in the meantime it iseasily influenced by the stray capacitance and tempreture. So doing research to achieveprecise measurement of the tiny capacitance has an important significance.The subject designs an overall capacitive liquid level measurement system basedon single chip microcomputer. Depending on the requirements of low powerconsumption, intelligent industry standard, we choose the NXP Company P89LPC936as the main microcontroller. Through the analysis of the principle of capacitive levelmeasurement, choosing non conductive liquid capacitive liquid level sensor, at the sametime, we respectively devise three measuring circuit that is oscillation circuitmeasurement method, measurement method and integral circuit impedance analysismethod to complete the accurate measurement of capacitive level sensor.First of all, this paper mainly introduces the overall design of the capacitive levelmeasurement system and related hardware circuit modules mainly including signalgenerating circuit module, power supply and current output circuit module, MCU andperipheral circuit module, temperature measurement module, as well as analysing theprinciples and functions of the module implementation. Then the paper describes theoverall structure of software design and achievement of each sub-module programming.At last, we test the designed capacitive level meter and make a comparision and analysisof three measuring circuits’ actual measuring data.Through analysis show that the measurement system can work stable and reliable,the design of three methods of measurement circuit basically achieves the measurement standard. The best measuring effect is the oscillation circuit method, owing to higherresolution, accuracy, stability, and its range of error can be controlled within2mm.by means of subsequent algorithm optimization can reach higher precision.