A sampler for use in the control extraction of material samples from a flow stream of particulate material within a tubular conveyor. A rotatable extractor extends through a sample aperture in the body of the conveyor and when actuated will permit the periodic capture and discharge of particulate material samples of a controlled size from the flow stream to a sample discharge outlet outside of the conveyor. The rotatable extractor does not interfere with any material flow assistance device within the conveyor, and in operation of the conveyor, the extractor will capture periodic samples from the operating flow stream for discharge at the sample discharge outlet. The rotatable extractor could comprise an extractor flighting, extending into the flow stream and out through a discharge tube or might comprise a rotationally mounted extractor to adapted to permit periodic sampling during rotation of the tube.