The Research And Design Of The Benchmark System For Water-level Instrument

The benchmark system of water-level instrument is an automation instrument with high precision, can be used to make the verification about water-level instrument. Nowadays, this kind of equipment is out of date and can’t meet the needs of reality. It has a low precision-usually centimeter-level in ten meter and low automation. The benchmark system adopts intelligent control method, select advanced control strategy, choose hardware and software with high quality, achieve the high precision calibration. After the comparison, this system could offer a verification certificate, using as a standard calibration instrument.In the thesis, a portable automatic calibrator for water level gauge which can be set simulative parameters and precipitation was designed. The calibrator for water level gauge, consists of water supply and drainage unit, standard water level units, water pump, frequency transformer, industrial personal computer, a servo valve and the man-machine interface. To simulate a water-level change of the outside environment for verification, we build a measuring-well. Water-level control unit can do this work:change the water supplication to achieve different circumstance, completing simulation of rivers and lakes. Standard water level unit, as the standard system, getting the water level data will be used as source data, take a comparison with the data from tested machines, and offer an error curve. Industrial personal computer controls the PLC and frequency transformer, makes an order to frequency transformer to change the rotational speed of water pump, order to PLC to select whether turns on the solenoid valve or not, using the servo valve and the man-machine interface software to complete the verification by setting the parameters automatically.As the need is high accuracy, so this thesis adopts the Fuzzy-PID control method, and using MATLAB as the simulation software. Making a comparison between PID control method and Fuzzy-PID control method in this control system, as the result shows: Fuzzy-PID method makes a really good performance-Paster response, short rising time, non-delay, small overshoot, strong perturbation resistance.At last, this thesis makes the error analysis on the system, adopts the uncertainty analytical method, makes that the consequence is convinced.After simulation and error analysis, it shows that, using the computer to control the whole process of verification according to the rules of predefined advanced strategy, the system has a considerable enhancement in precision, can meet the national primary standard-less than three millimeter in ten meter, and has an high automation, cuts down the part of human labor, increases the efficiency and calibration quality, and larger economic benefit and the actual value.