Measurement System Of Low Wind Speed And Direction

The measurement and control of the wind’s velocity, flow and direction play an important role in human lives. At present, the main measuring dev ice includes mechanical anemometer, Pitot tube anemometer, Doppler veloci meter, particle image velocimeter, strain gauge anemometer, Hot wire/film an emometer, Hot pulse anemometer and so on. Hot wire/film anemometer is a common method of measurement, because of proven technique, the good re solution and stability. At present, the main breeze’s anemometer comes from abroad, the price of the anemometer is very expensive, and there is a few of anemometer which can measure direction, this paper design a measurem ent system of hot film, aimed at measurement of the breeze’s velocity and direction. The hot anemometer’s principle of operation is this paper’s found ation. At first, the paper, based on thermodynamic, analyses the process of plate’s heat transfer in forced convection of the air stream, builds mathemat ical model of hot wire anemometer and the accurate calculation method. Usi ng temperature sensibility of the platinum resistance conducts the measureme nt and control of temperature, then measure sensor’s heat transfer in forced convection. Choose substrate material of the probe, by way of comparing physical characteristics of the different insulation material, such as coefficie nt of linear expansion, thermal conductivity coefficient, and considering bloc king effect, the convenience of install and use as well as other factors desi gn the probe construction of sensor.The important part of system is measurement system’s hardware and so ftware. In this paper, measuring the environment temperature is to temperatu re compensation for measurement system, using imbalance bridge and digit PID control algorithm make the bridge keep the constant temperature differe nce. In order to reduce error and the interference of measurement in the c ircuit, adopt three-wire connection method and interrelated constant current power supply which stimulates platinum resistor to measure air flow temper ature and direction of temperature field. Use difference amplifier to bias bri dge voltage. Choose LPC1343based on ARM coretexM3as processor. Microcontrolle r use SPI port which connects to ADCs to get the information of probe, an d use I2C port which connects to DAC communication to control the tempe rature of bridge. At the same time, LPC1343play an important part in pro cessing data in the measurement system. It can send the data to user. Desig n various ports that user can choose. During the design of software, establi sh communication protocol and rule, then programming modularly.In the paper, experiment on design model and gain the data, using Mat lab fit mathematical model, the paper also includes system calibration and a nalyses how to choose the reasonable temperature difference.