flow line 13 and may be a pressure transducer or alternatively may be a flow transducer 0045 fig2 a is a schematic view of the pulser also called an oscillating shear valve assembly 19 for mud pulse telemetry the pulser assembly 19 is located in the inner bore of the tool housing 101 the housing 101 may be a bored drill collar in the bottom hole assembly 10 or alternatively a separate housing adapted to fit into a drill collar bore the drilling fluid 31 flows through the stator 102 and rotor 103 and passes through the annulus between the pulser housing 108 and the inner diameter of the tool housing 101 the stator 102 see fig2 a and 2 b is fixed with respect to the tool housing 101 and to the pulser housing 108 and has multiple lengthwise flow passages 120 the rotor 103 see fig2 a and 2 c is disk shaped with notched blades 130 creating flow passages 125 similar in size and shape to the flow passages 120 in the stator 102 alternatively the flow passages 120 and 125 may be holes through the stator 102 and the rotor 103 respectively the rotor passages 125 are adapted such that they can be aligned at one angular position with the stator passages 120 to create a straight through flow path the rotor 103 is positioned in close proximity to the stator 102 and is adapted to rotationally oscillate an angular displacement of the rotor 103 with respect to the stator 102 changes the effective flow area creating pressure fluctuations in the circulated mud column to achieve one pressure cycle it is necessary to open and close the flow channel by changing.