Patent ID: 7388666

Claim:
A probe assembly used in testing instruments for determining optical signal within a test cell, comprising: a top plate( 2 ; 205 ) with a through-hole therein( 52 ; 250 ); an optical pickup( 1 ) for connecting with a photoelectrical converter and for picking up optical signal within a test cell being detected and sending said optical signal to said photoelectric converter converting said optical signal to electric signal, wherein the position of said optical pickup is fixed in relation to said top plate, the lower end of said optical pickup is inserted into said through-hole ( 52 ; 250 ) of said top plate, during detection more than one test cells adjacently arranged or integrally connected are delivered by a transporter mechanism ( 29 ) to the position where one of the test cells is exactly under said through-hole of said top plate with the top mouth of said one of the test cells being exactly aligned with the lower end of said optical pickup, so that the optical pickup picks up the optical signal within said one of the test cells; characterized in that the probe assembly further comprises: a cylindrical light hood ( 2 ; 202 ) having a central channel ( 21 ; 221 ), partially inserting into said through-hole ( 52 ; 250 ) of said top plate, and constructed in such a manner that the lower end of said optical pickup is inserted into said channel and surrounded by said light hood and that said light hood can slide down and up along the longitudinal direction of said optical pickup and said through-hole within a small distance between a protruding position and a retracting position, wherein said light hood lies in said retracting position through sliding up, while said light hood lies in said protruding position through sliding downward, during operation, when the one test cell, of which the sample is to be detected, is delivered by said transporter mechanism to the position where it is exactly under said through-hole and aligned with the lower end of said optical pickup, the light hood lies in the protruding position through sliding downward, the size of the lower end of said light hood tightly matches the size of the top mouth of said test cell so that the light interference from the adjacent test cells and surroundings with (to) the determination of the test cell being detected can be avoided by isolating said one test cell from its adjacent cells and surroundings by the lower end of said light hood when said light hood is in said protruding position.