| The measurement of flow velocity is a fundamental work in fluid mechanics. Hot-Wire Anemometer(HWA) , Laser Doppler Velocimeter(LDV) and Particle Image Velocimeter ( PIV ) are three representative technologies up to now, which are the results of technician's hard work and efforts. However, there are a lot of cases that trouble us and require us to develop new measurement technology. It is difficult to measure flow velocity in many fields such as aerodynamics, hydraulics, thermodynamics, and in boiler, flue or high temperature flow, and so on. All these difficulties impel us to pay more attention to new technology and develop a new theory. Because the questions are various, and the methods for measurement are limited, the correlative technology must be improved and developed.Currently, cross-correlation theory is a novel technology in current velocity measurement and is more potential, prospective, especially in "difficult" fluid.Based on relevant signal theory in flow velocity measurement, some usual signals such as capacitance, light, sound wave and pressure, and other unusual signals are adopted. Among these usual signals, the capacitance and light signal, which developed in 1960s and studied fully, could be used in fluid containing granules. Other signals (sound wave), which were used to measure velocity in river and sea current, began to be adopted lately in 1990s and developed. As for the pressure signal, in China, there is only one application, which the pressure signal is utilized to measure velocity in high temperature fluid containing granules in industrial field. Therefore, developing a new measurement approach based on the relevant theory is the main purpose of this paper.Combining the virtual instruments and the pressure cross-correlation principle, LabVIEWTM7.0 is used to build a flow velocity instrument, and made up a flow velocity instrument to measure velocity online. The concepts,development, actuality and process of virtual instruments are introduced in the paper at first.In this paper, the principle of pressure, which can be measured by cross-correlation in fluid flow, is discussed. And the instrument equipment is designed by the author. The work is explorative because the paper about the velocity measurement with pressure cross-correlation has not been found by author. The velocity instrument designed in this paper is not fixed on the instrument which can be used on practice. The following questions have been focused on: How much is immobile pressure caused by airflow in all kinds of situation? How much are the coefficient of cross-correlation and the precision? And so on. These causes are not clear. These questions are answered one by one in this paper. The software and hardware of the equipment are mentioned, and the experiences on signal disposal are depicted. The paper includes calculation of test results, corresponded graphs of drawing and analyses of the errors. The fluctuation of flow always exists, but it is difficult to be measured. For example, the turbulence intensity is small in wind tunnel, its effect could be better when added a proper artificial turbulence. In many industry fields, the pressure flow is enough to be measured. The results indicate that the measurement error is rational if the correlation of pressure signal is well. The instrument can be used on many flows because the flow velocity and pressure are universal. The expectation of the instrument is predicted in the paper finally.There are two innovative points in the paper: One is combination of the pressure cross-correlation technique and virtual instruments, another is an original creation of measurement equipment with two tiny pressure sensors. Comparing with the results of others, our testing precision is improved. It proved that the measurement technique based on pressure cross-correlation is practicable, and the virtual instrument is a strong tool in the velocity measurement. The paper provides a base to the velocity measurement with pressure cross-correlation in the future.
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