Experiments are made to study the drag and flow characteristics of three different types of instruments （flat type

streamline type

three-curve type）.The resluts of measurement show that the higher pressure difference signal

the lower losses and better stableness can been obtained by using this kind of non-standard unit.Furthermore

characteristics is effected by the area ratio M and the diffusion angle α.Of these kinds of instunment

at a low α number the flat type can obtain the highest pressure difference signal.The streamline type can obtain the lowest output pressure difference signal

but with the best stableness.However

the characteristics is on the contrary

at a high α number.