| 摘要 |
<p>The invention relates to an apparatus capable of observing an object in the path of a liquid stream whilst a radiation receiving part of the apparatus is positioned in the liquid stream. In a preferred form the invention relates to an apparatus capable of monitoring an excavation, which uses a high velocity liquid stream as the means of excavation, whilst the excavation is in progress, the invention comprising radiation receiving means for observing an object when the radiation receiving means is in a clear liquid stream flowing towards the object, the radiation receiving means comprising an observation window and cavitation prevention means disposed adjacent the observation window downstream thereof, the cavitation prevention means substantially assuming the shape of a zone of cavitational probability of a downstream end of the radiation receiving means when in a liquid stream of a selected velocity at which cavitation is possible, said cavitation prevention means thereby preventing cavitation when the liquid stream passes said downstream end of the radiation receiving means at or below the selected velocity.</p> |
