Research On Integrated Intelligent Averaging Pitot Tube Flowmeter

The Averaging Pitot Tube flowmeter is widely applied for its simple structure, convenient installation, little pressure loss, low cost, long-term stability. But it also has some limitations: need the cooperation of three valve group, pressure pipe and differential pressure transmitter which is very expensive and heavy to complete flow detection. The meter factor of Averaging Pitot Tube flow sensor is not a fixed value, it changes with the flow velocity, which will bring some error. But in industrial site often take it as a fixed value, which cause a narrow flow measured range of lower than 10:1. It can't meet the requirement of mass flow measurement. Additional pressure sensor and temperature sensor is still need to be installed if the customer want to monitor the conditions of temperature and pressure. In order to solve the problems, the research on Integration Intelligent Averaging Pitot Tube Flowmeter is carried on.In this project the information processing unit is made up of microcontroller MSP430 to realize the flow signal processing, amending, display and remote transmission, and the integration structure is designed also.The differential pressure, pressure and temperature signal are detected by HT20V differential pressure sensor, HT19V pressure sensor and LM135 temperature sensor separately. Curve fitting method is used in the system to reduce the error caused by the nonlinear characteristics of the signal. Hardware filter and software filter are used in the system to solve the problem of interference. In order to solve the problem of narrow flow measured range caused by the change of the meter factor, the system uses segmented linear method to fix meter factor. The temperature and pressure compensation scheme is made in this subject to achieve the automatic correction because the measurement result is sensitive to environmental temperature and pressure. The density is measured in use of pressure sensor and temperature sensor and the problem of quality flow measurement is solved.The signal acquisitions of differential pressure, pressure and temperature are realized in this system. 24 V power supply, 4~20 mA current outputs in two-wire are achieved. The system has liquid crystal display which can observe instantaneous volume flow, instantaneous mass flow, accumulated mass flow, temperature, pressure, differential pressure, density, meter factor and so on. The system has three buttons for the users to implant the meter factor and to make display switching. The system has RS485 communication to realize the long distance transmission. In order to ensure the stable operation, the system has extra watchdog circuit and power protection circuit.